Meteorology2

20. Satellite Imagery: what is being sensed, types of imagery, how clouds are depicted
 * Satellite imagery is primarily visible, infrared, and water vapor imagery.**


 * __Visible imagery__ senses brightness (a function of illumination and albedo). It can be used to detect cloud types which can help identify areas of developing convection. For example, clouds with water droplets have higher albedo than clouds with ice crystals. It can also be used to locate fog and stratus clouds, determine low level wind direction by looking at the alignment of cumulus fields, and identify cold fronts and thunderstorm outflow boundaries. It is essentially what you see from space and is dependent on the sun’s reflection off the clouds, thus cannot be used at night.**
 * __Infrared imagery__ is based on temperature. Dark areas on IR imagery are warm; white areas are cold. It is not useful for monitoring low stratus clouds or fog as they generally take on the same temperature as the ground. IR imagery is important in monitoring the progress of weather systems and determining if systems are becoming more intense or weakening. Since it is based on temperature, it can be used round the clock.**
 * __Water vapor imagery__ senses radiation, in particular in the 6 to 7 micron band, since water vapor tends to absorb radiation in this band. Strong radiation (dry) shows as dark on water vapor imagery and weak radiation (moisture) shows as white. It does not necessarily detect clouds as there can be moisture in the atmosphere before clouds form, and can actually be poorer quality when clouds are present. It only works well at the middle troposphere level (12,000 to 25,000 ft) and works best in warm atmosphere.**
 * (from Weather Map Handbook)**
 * IB**
 * I would like to add:**
 * VIS Imagery:**
 * Outer Space appears black
 * Except for thin cirrus clouds, clouds are bright white
 * Most water is dark (sun glint can brighten it considerably)
 * Land varies in brightness depending on snow cover, vegetation, soil moisture, etc.


 * // Infrared (IR) Satellite Image //**
 * ** s **pace is white (cold)
 * high/deep clouds are white
 * Low clouds are gray, often indistinguishable from the surface sun glint can brighten it considerably
 * surface (land or water) varies in brightness depending on temperature


 * //Water Vapor (WV) Satellite Image//**
 * Space is white (cold)
 * High/deep clouds are white
 * Low clouds are not visible
 * There is considerable variation in brightness in clear air depending on mid- to upper-level moisture and/or temperature


 * Stratiform clouds**
 * stable atmosphere
 * May be accompanied by steady light rain, drizzle, or snow grains
 * On satellite imagery: these appear smooth, have flat tops, and lack an organized pattern
 * VIS imagery: broad, flat on
 * IR imagery: absent (includes fog).


 * Cumuliform clouds**
 * Unstable atmosphere (air is rising and sinking)
 * Denotes an updraft
 * appear irregular and puffy or cotton like
 * Where a cumuliform cloud is present, the air is rising, and in the cloud-free air between clouds, the air is sinking.
 * VIS imagery: lumpy due to shadowing, often irregular shaped clouds
 * IR imagery: dark to medium gray, detailed features are washed out.


 * Stratocumulus clouds**
 * inversion (warm layer aloft) prevent vertical development of a cumulus cloud
 * may be aligned in sheets, lines, street patterns
 * VIS: appear bright and lumpy
 * IR: medium gray
 * Towering Cumulus and Cumulonimbus clouds**
 * Rapidly rising air causes cumulus clouds to grow tall (Tower)
 * Reach tall heights and encounter upper-level winds which blow the tops blown downwind producing a cumulonimbus cloud
 * satellite imagery: appear globular, carrot shaped, or triangular shaped. Shape is determined by the speed of the upper level winds.
 * VIS/IR: very bright; lumpy shadowed area seen on top of this cloud mass, denotes an overshooting top.


 * High-level (cirro) clouds**
 * Winds spread ice crystals across the sky
 * Appear wispy
 * VIS: fibrous, with the ground visible below
 * IR: very bright due to low temperature


 * Cirrostratus clouds**
 * smooth with uniform tops
 * VIS: light gray
 * IR: bright.


 * Cirrocumulus**
 * cellular in shape, and are often too small to be resolved on IR or Visible imagery


 * Other Information about Satellite imagery (not sure if this is needed?)**
 * Cloud Element -** Smallest cloud form that is resolved by a satellite image.


 * Cloud Shield -** Broad cloud pattern that is no more than 4 times as long in one direction as it is wide in another.


 * Cloud Band –** A nearly continuous cloud formation that has a long distinct axis. The ratio of length to width is at least 4 to 1. The width of the cloud band is > 1° of latitude.


 * Cloud Line -** Narrow cloud band with individual cloud cells connected. A cloud line width is < 1° of latitude.


 * Cloud Street**
 * Narrow cloud band with individual cloud cells //not// connected
 * The cells line up parallel to one another along low-level wind flow/direction.
 * Each street is < 1° of latitude in width.
 * A type of organized convection that contains an extended line of cumulus clouds (often in an otherwise partly cloudy sky).
 * Various sources of thermals spaced across the wind may give rise to parallel cloud streets
 * Produced in an air mass in which the convection layer has a well-marked top and in which the wind direction is almost constant
 * Distance between adjacent streets has been observed as about three times the height of the inversion or stable layer
 * A single line of cumuli often extends to more than 100 km downwind
 * Up to 100 nearly parallel lines of cumuli have been observed.
 * **Requirements for development**
 * Surface winds of 10 - 15 kt
 * Wind direction nearly constant with height in the convective layer
 * An inversion or stable layer to limit the vertical development of convective currents, usually at a height of 1.5 to 2 km, and speed curvature of the wind profile.
 * The wind speed should increase with height to a maximum of at least 10 m/s in the middle or upper part of the convection layer. Above these levels the wind may decrease or increase again.


 * Cloud Finger**
 * Extension from the forward side of a frontal cloud
 * band of clouds along a front
 * Finger extends south of this band associated with the low level jet and corresponding pressure drop


 * Comma Cloud -** Vortex with one or more spiral clouds. Spiral clouds converge toward a common center.


 * ZA** **Enhancement** - modify the “ends” of the temperature/grayscale where clouds do not normally form

JI
 * MB curve** (mid-latitude thunderstorm curve) - shows contrast near the tops of thunderstorms (i.e. look for the deepest convection). This is used to properly identify a Mesoscale Convective Complex.

21. Radar Imagery and principles: how it works, what it detects, various products.
 * Weather Radars**
 * **broadcast a brief intense pulse of energy followed by a relatively long “listening period” during which time energy reflected from targets is received and processed**
 * **target distance is determined**
 * **R = c x (et/2) where R = range, c = speed of light, and et = elapsed time**
 * **Rmax = ½ distance electromagnetic energy can travel between pulses**
 * **the rate at which pulses are broadcast (pulse repetition frequency or PRF) is expressed in # of pulses/second**
 * **Reflectivity - power returning to the radar is processed and displayed to indicate target “reflectivity”; Radar reflectivity is a measure of the efficiency of a target in intercepting and returning the electromagnetic wave**
 * **Reflectivity/Efficiency is dependent upon target: Size, State (frozen, liquid), Concentration, Shape (snowflake, raindrop)**
 * **Equivalent Reflectivity - Defined as the concentration and uniformly distributed small diameter water drops which would return the amount of power received**
 * **radar can determine # of drops and size of drops in a given volume: calculate amt of rain falling**
 * **Subrefraction - beam is refracted less than it would be in a standard atmosphere (bent toward the Earth less).**
 * **Superrefraction - beam is refracted more than it would be in the standard atmosphere (bent toward the Earth more)**
 * **bright band – radar feature which appears when the beam intersects snow melting into rain, leading to enhanced reflectivity**


 * Products**
 * **base reflectivity - reflectivity at specific angle**
 * **composite reflectivity: highest reflectivity for each grid for all elevation angles, lower resolution. Used to identify the strongest storm within multiple storms.**
 * **echo tops: locates the highest elevation angle where the reflectivity > or equal to 18.3 dBZ**
 * **Vertically integrated liquid – useful to determine the threat of hail**
 * **Velocity Azimuth Display (VAD) – determine changes in storm relative helicity within the environment (p. 72 in Weather Forecasting Handbook)**
 * **Tornado Vortex Signature (TVS) - used to identify Pulse Storms. The Pulse Storm has rapid development and short lifespan make it one of the hardest to warn for. The main threats include a brief period of hail (Normally an inch in diameter or smaller), brief downburst winds, and possible weak tornadoes**
 * JI**


 * I'm adding two more.**
 * Doppler Radar products:**
 * Radial/Relative Velocity (general motion of storm toward/away from radar) and Storm Relative Velocity (circulation/motion within storm, red = out and green = in, possible cyclonic circulation where brightest greens/reds). See #22 answer for more information.**
 * JA**

22. Radar signatures (hook, bow-echo, etc.) and what each indicates in terms of severe weather


 * Hook Echo**


 * **Radar signature used to predict tornadoes.**
 * Classic Supercell hook echo on radar**
 * **Grey colors (heaviest precipitation around center spin) wrap around due to rotating updraft**
 * **Rotating updraft pushes mass up into atmosphere and some of the mass is carried off by the upper level winds**
 * **As it rotates it grabs some of the precipitation falling in grey shaded part (forward flank) an pushes it around the backside of the storm creating a hook echo**
 * LP (Low Precipitation) Supercell hook echo on radar**
 * **difficult to identify on radar because it has much smaller hook echo**


 * Squall Line (p. 128 in Lutgens)**
 * **triggered as a line or organize into a line from a cluster of cells**
 * **Typically develops in response to: Unidirectional Shear Environment (0 - 3km), Linear Forcing Feature: Front, Trough, or Dry Line**
 * **CAPE is usually 2200+**
 * **Mid-level flow is most commonly perpendicular to the forcing feature**
 * **Low-level flow is normally nearly parallel to surface forcing feature**
 * **As a result of the inflow direction look for the southern most storm to be most intense**
 * **Severe and non-severe storms have significant unidirectional shear, but severe squall lines usually develop in more unstable environments.**
 * **the greater the shear is perpendicular to the line, the longer-lived the squall line will be**
 * **straight line hodograph: faster winds aloft**
 * **Greatest threat: damaging winds, however tornadoes can and do occur**
 * **Classic evolution of squall line with weak shear between 10 – 18m/s: evolves from a narrow band of intense convective cells to a broader, weaker system over time, the squall line doesn’t move fast enough to keep up with gust front which cuts off inflow**
 * **Classic evolution with stronger shear (>18m/s): environments produce stronger long-lived lines composed of strong leading line convective cells n even bow echoes, the updrafts are tilted forward. The inflow to the line is maintained and the squall line continues.**
 * **low level inflow supports updraft (from the east), downdraft produces rain, hail, wind, if cold pool advances out it can cut off inflow**
 * **The surface cold pool is a mass of air in center of storm (cooled off and denser than surroundings). The surface cold pool sinks to ground. This downburst forms high pressure on the ground whihc pushes out to create the gust front. The gust front forms drag (friction) and rain-cooled air (evaporation in a dry layer) drops to the surface amidst the downdraft. This produces a meso-high which drives the gust front forward.**
 * **Rear inflow jet – occurs due to the dynamic between the cold pool and the warm air forced to rise above the gust front. The RIJ is brought to the surface as a downburst. The location of descent depends on shear and CAPE. Gravity increases its speed near to surface. In weak wind shear conditions, the RIJ descends well behind the gust front and the squall line weakens. In strong shear conditions, the RIJ descends near the gust front and the squall line is prolonged. If the temperature between the warm air and cold pool is great (high CAPE), the RIJ increases.**


 * Bow echo (p. 130)**
 * **a bulged (faster winds) segment of squall line**
 * **apex of bow = area of strongest winds/greatest damage**
 * **rear inflow jet - stronger mid-level winds push out center of squall line creating an apex and bookend vortices**
 * **The southern vortex spins anticyclonically and northern vortex spins cyclonically. These vortices can produce tornadoes that are usually weak and short lived**
 * **the stronger mid-level winds transfer momentum down to surface and push the precipitation outward. The further the precipitation advances, the faster the winds. This creates an area of enhanced evaporation = stronger downdraft brought to surface**
 * **high CAPE indicates greater contrast between the warm air ahead of the system and the cold poll. This strengthens the RIJ**
 * **Early detection: look for weak echo channels at the rear of a squall line or squall line segment. Weak echo channels indicate enhanced evaporation which can lead to a potential increase in the downdraft winds. The enhanced downdraft can pull the mid-level momentum to the surface.**
 * **Next, look for a bow in the forward outflow boundary. This suggests that surface flow has increased. A bow in the main line will follow as surface forcing follows the outflow boundary.**
 * **Tornadoes can form along the apex of the bow as horizontal vorticity is tilted into the vertical. These tornadoes are normally weak and short-lived. These may be difficult to detect on velocity products as circulation is normally weak and shallow, and they can be masked by the overall storm flow.**


 * 3****-Body Scatter**
 * **In the 3-body scatter, radiation is scattered from a hail core to the ground, back to the hail core, and back to the radar.**
 * **The extra distance traveled by the radiation creates a false echo which extends from the hail core outward (away from the radar)**
 * **The false echo is known as a hail spike**


 * I think the following are products, but I need to verify this.**
 * Radial Velocity**
 * **The component of target motion parallel to the radar radial (Azimuth).**
 * **It is the component of a targets motion that is either toward or away from the radar site along the radial**
 * **Determined by analyzing the phase change of two successive pulses**
 * **Allows user to see the motion of targets relative to the stationary radar.**


 * Storm Relative Velocity**
 * **The component of target motion parallel to the radar radial (Azimuth) corrected for storm motion. Allows the user to see motion relative to a moving storm (i.e. motion within the storm).**


 * MARC (Mid-Altitude Radar Convergence)**
 * **Convergence at the mid levels – locally enhanced convergent areas (velocity differentials) found embedded within a larger region of convergence extending from 60 to 120 km in length, 2 – 6km in width, depth averaging 6.2 km (from 3-9km) in height, and maximum convergence found at the mid-levels of the storm (between 5 – 5.5 km in height).**
 * **The magnitude has typical velocity differences of 25 -50m/s (50 -100kts)**
 * **Convergence: some will flow down to ground creating strong surface winds**
 * **the MARC signature: weak echo channels indicate evaporative cooling n on radar areas of outbound and inbound coming together**
 * **cyclonic and anticyclonic patterns on p. 42 of Weather Forecasting Handbook**
 * JI**


 * I can verify that Radial Velocity (general motion of storm toward/away from radar) and Storm Relative Velocity (circulation/motion within storm, red = out and green = in, possible cyclonic circulation where brightest greens/reds) are Doppler Radar products according to my notes.**
 * JA**

23. Hurricanes: stages, typical sites of development, seasonality Looks good. JL
 * A tropical cyclone (hurricane) needs five components in order to develop: deep (~ 150’), warm (79 degrees F+) ocean waters, coriolis (higher than 5 degrees latitude), converging (low pressure) surface winds, upper level divergence (high pressure), and weak wind shear (weak winds aloft). There are four stages of development that a tropical cyclone must go through in order to become a hurricane. These are Tropical Disturbance, Tropical Depression, Tropical Storm, and finally Hurricane. Tropical disturbances originate as thunderstorms in the tropics or subtropics. They may also be known as easterly waves. They must last for at least 24 hours, be 200-600 miles in diameter, have an open or broad circulation, and are given no wind speed designation. Tropical depressions have maximum sustained surface winds of 38 mph; and a closed tight circulation. Once maximum sustained surface winds are between 39 – 73 mph, the tropical cyclone is now considered a tropical storm, and is given a name. A hurricane develops when the maximum sustained winds are greater than or equal to 74 mph. At this point, and eye is usually visible. **
 * MLS **


 * Add to Hurricanes: Develop between 5 degrees latitude (not closer to equator as they need the Coriolus effect for rotation) and less than 20 degrees latitude as they need the 80 degree sea temperature. Can form in any tropical sea except the South Atlantic and South East Pacific which are too cold. Convergence at ITCZ, or in the Easterly Wave provides lift needed to cause condensation and latent heat release from condensation. Hurricanes develop low pressures at surface from the warm rising air, and high pressure aloft which allows for diverging air helping to draw moisture and heat in below. Hurricanes are heat engines and rely on that maintained influx of heat and moisture---thus they decay when they cross over cold water, cross over land which cuts the moisture input and land friction causes decreased wind speeds, or when the large scale flow aloft is impinged cutting inflow. **
 * (Lutgens 315-316) LK **


 * Looks good. I would add that, in the U.S. official hurricane season is June through November with the majority of hurricanes occurring from August through October. Hurricanes in the northern hemisphere tend to occur between June and December; in the southern hemisphere between January and March. (Lutgens, p312)**
 * IB**

24. The Skew-T/log p diagram: data plotted, various lines, use in forecasting, calculation of various indices and values:


 * __Isobars__ -- Lines of equal pressure. Solid brown lines that run horizontally from left to right and are labeled on the left side of the diagram. Pressure is given in increments of 100 mb and ranges from 1050 mb to 100 mb. Spacing between the isobars increases in the vertical because of the log scale that is used to represent pressure.**
 * __Isotherms__ -- Lines of equal temperature. Straight, solid brown lines that slope from the bottom left to the upper right (thus the name skew) across the diagram. Increments are per degree and are labeled for every 5 degrees in units of Celsius. They are labeled at the bottom of the diagram with corresponding temperatures in Fahrenheit.**
 * __Dry Adiabats__ -- Slightly curved, solid brown lines that slant from lower right to upper left. They are labeled every 10 degrees Celsius and indicate the rate of change of temperature in an air parcel of dry air rising or descending adiabatically.**
 * __Saturation Adiabats__ -- Slightly curved, solid green lines sloping from lower right to upper left. They are labeled every 2 degrees Celsius and indicate the rate of change of temperature in a saturated air parcel as it rises pseudo-adiabatically. They become parallel to the dry Adiabats at the top of the chart because of the very low moisture content at those levels and stop at 200 mb.**
 * __Saturation Mixing Ratio Lines__ -- These are the dashed green, slightly curved lines that slope from the lower left to the upper right that represent lines of equal mixing ratio. They are labeled on the bottom of the diagram in grams per kilogram of water vapor. They extend only to 200 mb and the spacing between them decreases as their values increase.**
 * __Temperature Curve__ -- This is the plot of the temperature measurements that were taken from the rawinsonde as it was increasing in height. This curve will always be to the right of the dewpoint curve as you are facing a Skew-T. It is usually drawn in red but can be other colors.**
 * __Dewpoint Curve__ -- This is the plot of the dewpoint measurements increasing with height. This curve will always be to the left of the temperature curve as you are facing a Skew-T. It is usually drawn in green but can be other colors.**
 * __Lapse Rates__**
 * __Environmental lapse rate__ - The rate of decrease of temperature with height of the atmosphere surrounding the parcel).**
 * __Dry adiabatic lapse rate__ - The rate of decrease of temperature with height as an unsaturated parcel of air rises adiabatically. Typically -9.8 ºC/km.**
 * __Moist adiabatic lapse rate__ - The rate of decrease of temperature with height as a saturated parcel of air rises pseudo-adiabatically. Can range from -4 ºC/km to -9 ºC/km but an average value is about -6 ºC/km.**


 * TOTAL TOTALS**
 * <44 Convection not likely**
 * 44-50 Likely thunderstorms**
 * 51-52 Isolated severe storms**
 * 53-56 Widely scattered severe**
 * >56 Scattered severe storms**


 * K INDEX**
 * 15-25 Small convective potential**
 * 26-39 Moderate convective potential**
 * 40+ High convective potential**


 * CAPE**
 * 1 - 1,500 Positive**
 * 1,500 - 2,500 Large**
 * 2,500+ Extreme**


 * SWEAT**
 * 150-300 Slight severe**
 * 300-400 Severe possible**
 * 400+ Tornadic possible**


 * SR HELICITY**
 * 150-300 Possible supercell**
 * 300-400 Supercells favorable**
 * 400+ Tornadic possible**


 * LIFTED INDEX / SWI**
 * -1 to -4 Marginal instability**
 * -4 to -7 Large instability**
 * -8 or less Extreme instability**


 * BRN**
 * <45 Supercells favorable**
 * <10 Too sheared**
 * teens Optimum**


 * EHI**
 * EHI >1 Supercells likely**
 * 1 to 5 F2, F3 tornadoes possible**
 * 5+ F4, F5 tornadoes possible **


 * MCA**

**JA**
 * Use to see stability/parcel thermodynamics. Compare parcel with env by plotting parcels T and Td on skew-t log p. P decreases as you go up and parcel expands/cools. Based on 2 assumptions: 1. No compensating motions – the env doesn’t sink to take void’s place (however, the parcel mixes w/env when rising but effects are minimal), 2. Parcel doesn’t mix w/env and retains its ID. **

I found a short 7 minute video on Youtube that helped me review how to read a skew t log p sounding and figure out CAPE/stability of atmosphere:

JA**
 * http://www.youtube.com/watch?v=bOnGFHXkQ8w**

25. Constant Pressure Maps (850mb, 500mb, etc.): features found on each Looks good. JL Add: 850 and 700 mb show 30 meter height intervals and isotherms ( Temp in degrees C) and sometimes relative humidity >70%. Are used to predict min/max temperatures. (Lutgens 346) LK
 * 850mb map: 850mb maps depict the atmosphere at about 1 mile above sea level. This is where temperatures are effected by the warming and cooling of the earth's surface. These represent surface features for high elevation places like Denver CO. Cold and warm air advection is found on these maps. Warm air advection is associated with widespread lifting resulting in clouds and precipitation. Forecasters use the 0°C isotherm as the snow/ice/rain boundary. **
 * 700 mb map: 2miles above sea level. Steering mechanism for T-storms. Sometimes the 700mb map is used as a proxy for the 850 mb map in areas of high elevation. Rule of thumb: When temps at 700mb are 57° or higher, T-storms will not develop as it acts as an inversion or "cap". **
 * 500mb map: 5.5 km above sea level Here is where half the atmosphere is above and half is below. Troughs indicate storms, ridges indicate clear weather. Forecasters use these maps to show upper level low's within a trough indicating heavy precipitation. **
 * 300-200 mb maps: 6 miles above sea level. Here is where details of the polar jet are observed. 300mb during winter and early spring and 200 mb during summer because the jet is usually lower in winter. (pages 345-348 in "The Atmosphere" book) **
 * BW **

26. Severe Thunderstorm classification parameters Looks good. JL ( []) JI
 * A severe thunderstorm is classified by winds in excess of 58 mph //__or__// produce hail with diameter larger than 0.75 inches //__or__// generates a tornado. About 10% of all T-storms are severe. **
 * BW **
 * The requirement for hail diameter is now 1 inch (it was changed on January 5th, 2010). I verified it on NOAA's website. **

27. Supercell thunderstorm structure **There's a great diagram on page 284 of Lutgens.**
 * IB **
 * I'd like to add the following: **
 * Supercells are characteristically tall storms -- reaching way up into the stratosphere. The main updraft and downdraft mutually support one another leading to a long lasting storm.**
 * Supercells have a common structure:**
 * __A. Anvil-__ The Anvil is one of the most impressive features of a severe storm due to its areal coverage and icy texture. Within a severe storm, moisture is transported from the lower troposphere to deep into the upper troposphere. Not all moisture that is ingested into a storm is precipitated out of the storm. Some of the moisture in a strong updraft is lofted so high into the troposphere that it is not able to drop back down immediately. Strong upper level winds move and fan the moisture out over great distances. The temperature of the anvil is frigid cold. The light density of the moisture allows the wind to move it at will. A forecaster can note the direction and speed of the upper level winds by noting the anvil's orientation. The moisture within the anvil will be blown downstream.**
 * __B. Overshooting Top__- The core of the updraft has the strongest convective upward vertical velocity. This core of rapidly rising air will only slow down and stop when it encounters a very stable layer in the atmosphere. This very stable layer is the tropopause. Air will rise as long as it is less dense and therefore more buoyant than surrounding air. The faster air rises the longer it takes generally to slow down and stop once it encounters a very stable layer. This occurs because a moving object has momentum. That part of the updraft that has the greatest momentum will form the overshooting top on a severe thunderstorm.**
 * __C. Mammatus-__ Mammatus are pouched shaped clouds that protrude downward from the thunderstorm's anvil. They form as negatively buoyant moisture laden air sinks. The cloud remains visible until the air sinks enough that the relative humidity falls below 100%. The portion that has a relative humidity of 100% remains visible. Theories to how they form include: 1) turbulent eddies mixing down moisture, 2) evaporative cooling with surrounding air causes pockets of sinking air, 3) Pockets of precipitation falling out of the anvil that produce virga. Mammatus tend to be most prominent in extremely severe storms but can occur when storms are not severe also. Click here for an image of mammatus clouds.**
 * __D. Flanking Line__- The flanking line is produced by convergence along an outflow boundary extending from the storm. This outflow is often air from aloft that is converged into warm and moist air near the surface. It can be seen as a line of developing cumulus clouds extending from the storm. The cumulus closer to the storm tend to be more mature and eventually merge into the parent storm. The flanking line often feeds into the updraft of the storm.**
 * __E. Rain Core / Hail Core__- The core refers to the heaviest precipitation. The most violent rain and hail in a supercell tend to be on the outer edge of the updraft on the downdraft side of the storm. Extreme turbulence on the edge of the updraft can contribute to significant hail growth. As hail falls into above freezing air it sheds its moisture as rain.**
 * __F. Wall Cloud__- The wall cloud is located in the updraft region of a supercell. Rising air cools and condenses out moisture once it is saturated. Due to the rapidly rising air and the verticality of the rising air, the cloud base is close to the ground within the wall cloud. The wall cloud will often be witnessed as rotating since directional wind shear acts on the updraft as it rises. Tornadoes can occur under the wall cloud.**
 * __G. Rain-Free Base__- The updraft region in supercells will often lack precipitation. This is most true for developing supercells and for classic/LP supercells. As a supercell matures or has a high moisture content, often precipitation will wrap around the updraft region and eventually fall into the updraft region. The updraft region of a supercell will be tilted with height. This will deposit the precipitation away from the updraft and thus this also results in less precipitation in the updraft region. Being in the rain free base region offers an awe-striking view of the storm.**
 * __H. Forward Flank / Rear Flank Downdraft__- The forward flank downdraft is the outflow from the rain-cooled air of the storm's downdraft. The rear flank downdraft is air from aloft that is transported down to the surface from colliding with the storm. The rear flank downdraft air tends to be dry and warm since the air warms by adiabatic compression as it sinks to the surface. Adiabatically warmed air will also decrease in relative humidity if no precipitation falls into the air. The rear flank downdraft tends to be warmer than the forward flank downdraft also since rain the evaporational cooling is not as common in the rear flank. Shear is enhanced along these flanking downdraft boundaries and the shear can be magnified along where the two flanks merge. The right balance of shear and instability release can lead to tornadogenesis**


 * Another characteristic observable in both models and in nature is the large cloud free area above the base of the updraft known as the vault or Weak Echo Region. Rain and possibly hail fall to the ground outside this region, leaving the vault region relatively precipitation-free. In some supercells, one can sometimes observe both a v-notch and a hook echo. Some supercell thunderstorms also possess a clearly visible flanking line. The flanking line separates cool storm outflow from warm moist storm inflow and sits above the gust front. New storms form along the flanking line as the moist inflow air rises as it approaches the cool surface air.**
 * MCA**

28. Supercell thunderstorm types: common locations, greatest severe threat with each
 * Low Precipitation (LP) supercell: Since rain curtains and rain shaft remain small, vast portions of the cell are exposed for viewing. Although these can produce only small tornadoes, they can produce huge hail. **
 * Classic Supercell (CP): Moderate amounts of rainfall, tornadoes are common. Their rain curtains get wrapped in the mesocycle circulation producing the hook echoes observed on radar. These storms result from high instability and large storm-relative shear. **
 * High Precipitation Supercell (HP): Most violent supercell on earth. Produces rain wrapped tornadoes called "Bears Cage". Copious amounts of precipitation fall out of these storms. (pages 131-132 of weather forcasting handbook) **
 * BW **
 * Just want to add:**
 * Common locations for LP: western states (arid, high plains); CP: Great Plains; HP: around and east of Mississippi River due to abundant water vapor**
 * KMS **

29. Vorticity: types, how they are generated and change; advection and its impact on weather LK Vorticity is analyzed on 500 mb charts. Absolute vorticity= earth + relative vorticity Earth vorticity is caused by counter clockwise rotation which causes positive vorticity Relative vorticity is caused by curvature and shear. Curvature is the spin created by a parcel flowing through a ridge or trough. Shear is spin created by adjacent air streams moving at different speeds (think of the log in a stream example). Relative vorticity is independent of Earth's rotation, Absolute vorticity in the northern hemisphere is always positive.
 * Vorticity is set up by the changing wind speed with height (speed shear) or with the change in direction (directional shear). This sets up the vorticity or spin in a parcel of air. **
 * Positive Vorticity (in Northern Hemisphere) spins from on vertical axis from left to right and is generally related to upward vertical motion and storms. **
 * Negative Vorticity (In NH) spins from right to left and is generally related to downward vertical motion and clear skies/fair weather. **
 * You can have vertical vorticity like above, caused by troughs and ridges, wind speed and direction changes in vertical axis. **
 * You can also have horizontal vorticity, spin on horizontal axis, caused by change in wind direction and speed. **
 * Streamwise vorticity (helicity) is parallel to storm inflow and includes speed shear (as speed increases with height) directional shear (directions change wiht height) **

Negative and positive vorticity advection: As a parcel enters a vorticity field a spin is imparted. The Law of Conservation of Angular Momentum says that this spin will result in vertical stretching (like an ice skater). Horizontal convergence is created. As a parcel exits a vorticity field the spin decreases. The Law of Conservation of Angular Momentum says the decrease in spin will result in vertical compaction (the parcel gets "fat"). Horizontal divergence is created. Convergence and divergence and the associated vertical motions are most recognizable with vortcity in the base of a trough. Notably, there will be NVA entering the trough and PVA exiting. It is the PVA in the exit region of the trough that can lead to uplift at the surface and instability. -PM

30. Surface/Upper-level station plots (decoding)

31. Numerical Weather Prediction 32. Enhanced Fujita Scale
 * Pg 86 Vasquez Weather Map Handbook 2nd edition PB**
 * Numerical weather prediction is the science of predicting the future state of the atmosphere using physical equations. The technique was first proposed in 1923 and the first operational predictions were available by 1960. Depending upon the weather agency and its purpose, a model is run either at a coarse resolution which covers the globe or at a fine resolution with covers a small area like a continent. The worldwide model is referred to as global and the fine model is called a regional model. Detailed models exhibit considerable accuracy, but are limited by the huge amount of processing requirements. The forecasts derived from these models begin to deteriorate in a couple of days at most. Data to assemble these models come from four primary sources – government, academic, commercial, and hobbyist – sites on the internet. These models are not without error and bias and must be used by a skilled forecaster using an diagnosis of the atmosphere to develop a sound forecast**
 * The EF Scale is used to rate a tornado based on estimated wind speeds and related damage. When tornado-related damage is surveyed, it is compared to a list of Damage Indicators (DIs) and Degrees of Damage (DoD) which help better estimate the range of wind speeds the tornado likely produced. From that, a rating (from EF0 to EF5) is assigned. **
 * The EF Scale was revised from the orginal Fujita Scale to reflect better examinations of tornado damage surveys so as to align wind speeds more closely with associated storm damage. The new scale has to do with how most structures are designed. The EF scale is a set of wind //estimates// based on damage, not normal surface wind measurements. **

[])
 * **EF SCALE** ||
 * **EF Rating** || 3 Second Gust (mph) ||
 * 0 || 65-85 ||
 * **1** || 86-110 ||
 * **2** || 111-135 ||
 * **3** || 136-165 ||
 * **4** || 166-200 ||
 * **5** || Over 200 ||
 * KMS (I didn't include the Damage Indicators, but I can if you guys think it's necessary. Here is a link to the DIs: **

33. Saffir-Simpson Scale
 * Saffir Simpson Scale ranks relative intensities of hurricanes from 1 the least, to 5 the most severe. The National Weather Service assigns the rank on development of a hurricane. The ranking is used to notify the public of possible levels of storm damage if the storm were to make landfall without changing intensity. Levels are predicted for storm surge, wind speeds, and damage extent. Category rankings are updated as storm conditions change. (Lutgens, p 317) LK **

Good, but just thought I'd add the tidbit that a tropical storm is classified as a Category 1 hurricane once winds reach 74 mph (119 kph). KMS

34. The Three Primary Synoptic Air Streams: location, origin, contribution to severe weather
 * The classic 3 synoptic airstream setup requires __four necessary components__ in order for severe weather to develop. These are moisture, instability, lift, and shear. **


 * 1) **__Moisture__ is needed for clouds to form and precipitation to develop. High moisture levels provide latent heat, which causes instability, because moist air is less dense than dry air. High dew point levels lead to greater instability, and this can increase the potential for tornadoes by lowering LCLs.**
 * 2) **In order for severe weather to develop, positive energy is required. When warm, moist, less dense air lies beneath cold, dry, denser air, __instability__ will develop. Instability may be represented by CAPE (Convective Available Potential Energy). In any situation where you have a positive CAPE value, rising motion will occur so long as any lower inversions can be overcome. Higher CAPE values are associated with the potential for severe weather to occur.**
 * 3) **The third component, __lift__, is required to initiate a storm. Sources of lift include Positive Vorticity Advection, Upper and Lower Level Jets, fronts, drylines, and outflow boundaries, which are driven by cold pool generation from convection.**
 * 4) **Finally, __shear__ is required for severe weather to develop. Shear can be either speed or directional, and cause updrafts that can lead to strong tornado potential by supplying a steady supply of warm, moist air for the storm. Shear is measured using SRH (Storm Relative Helicity).**

I would add the following: Three Primary Synoptic Air Streams: 1) Surface to 900 mb, southerly component, originating off Gulf of Mexico or from gulf stream 2) 700 mb, southwesterly component, originating of Mexican plateau 3) 500mb, westerly component, originating in jet stream The surface to 900 mb component brings in warm, moist air, providing latent heat. The 700 mb component provides very dry air and creates a situation where warm, dry air is over warm, wet air and instability is increased. The 500 mb component provides lift, relieves updraft pressure and pushes the air mass to the North and East. (Week 8, Lecture 13a, my notes)  JL
 * When all of these come together, a low level airstream to usher in southerly moist air, warm dry air over the top of the warm moist air layer to create a capping inversion (allowing instability to increase), and the lifting mechanism and mass evacuation provided by an upper air Jet Stream, the recipe is there for severe weather to develop. **
 * MLS **

35. Stages of Tornado Development (Lutgens, p. 294) LK
 * Tornadoes form with severe thunderstorms (TS) and are most likely to appear in parts of the TS adjacent to large hail. Less than 1 % of TS produce tornadoes. **
 * Tornadoes form with the interaction between strong updrafts in the TS and winds in the troposphere. They can form with any severe weather—cold fronts, squall lines, hurricanes, but are most common with supercells. **
 * Steps of development include1) Mesocyclone develops---precedes tornado by about 30 minutes. In the mesocyclone the winds develop form the ground upwards and develop vertical wind shear, turning from southward to westward and increase in speed.2) Speed shear develops(faster winds aloft than below) producing winds that roll on a horizontal axis. (think Slinky along the ground)3) Strong updrafts may then lift those winds vertically. This stretches and narrows the mesocyclone and intensifies the winds (think ice skater pulling arms in on spin)4) The rotating air stretches down to form the WALL CLOUD and then the spinning vortex of the FUNNEL CLOUD. When the funnel touches the ground this is a TORNADO. **
 * Stages include: **
 * 1) **Development/organization (descends from wall cloud)**
 * 2) **Mature Stage (after touchdown, expanding funnel width. Max size and strength and destruction)**
 * 3) **Dissipating Stage (shrinking, tilt horizontal, path smaller, wall cloud dissipating)**
 * 4) **Decaying Stage (wall cloud vanishing, thin contorted or rope-like funnel)**


 * Want to add (from lecture notes) just as another point of view:**
 * Dust Whirl Stage: Circulation continuous from cloud to ground, vortex is invisible because pressure isn't low enough for condensation, visual identification=dust or light debris circulating at surface**
 * Organization Stage: Appearance of condensation funnel, descends toward the ground as pressure lowers toward the ground, tornado may dissipate at this stage**
 * Mature Stage: Vortex is at greatest size and intensity, wall cloud is well organized and wall cloud is visible, development of tail cloud, vortex breakdown is possible**
 * Shrinking Stage: Vortex diameter shrinks, rotation may increase, vortex begins to tilt with base lagging behind, wall cloud shrinks and di****sappears**
 * Decay Stage: Vortex becomes stretched like a rope, no wall cloud**
 * KMS**

36. Lightning: process of development, types, generation of thunder
 * A thunderstorm occurs when thunder is heard. **
 * Lightning develops when ice pellets form in the cumulonimbus cloud. When the pellets freeze from the other shell inward, the charge in water separates, making the outer frozen area + while the inner drop is negatively charged. The pellet freezes through, shatters and the lighter frozen shell goes to the top of the cloud while the heavier negative droplet goes to the bottom. The negatively charged cloud base repels the negative charges on the ground, making the surface positively charged. Lightning forms to balance these charges in both the upper cloud and the + charged ground.A lightning flash is several (~4) STROKES, each with a downward forming LEADER—the path, and a bright RETURN STROKE. The STEP LEADER is the extension of the leader due to the electrical potential increase from the + part of the cloud. Electrons flow down the leader from the cloud. The return stroke actually starts at the ground and goes upward. It is the bright flash we see. **
 * Thunder is the sound waves from rapidly heated, expanding air around the lightning channel. Lightning is seen instantly (speed of light) while sound is slower. A 5 second lag between light and sound = approximately 1 mile between you and the lightning. **
 * (Lutgens, 288)LK **

JI
 * I would like to add:**
 * The process ice pellets freezing, shattering, and (+) and negative charges separating is called the thermoelectric effect. Also, the negative charges can be found in the middle as well as the lower part of the cloud.**
 * Formation**
 * Lightning stroke begins when the electric fields exceed breakdown voltage
 * initially streams of electrons surge from the cloud base toward the ground in steps of 50 to 100m
 * start and stop steps form as the stepped leader progresses toward the ground
 * The stepped leader is very faint, essentially invisible to the human eye, produces an ionized channel that will allow for the flow of charge during the remainder of the lighting stroke. When the stepped leader gets near the ground (~100m or so), a positive charge moves from the ground up toward the stepped leader (these are called connecting leaders), the connecting leaders may come from almost any pointed object on the ground (trees, antennas, grass, flagpoles, telephone poles, people, really tall towers)
 * Positive lightning**
 * Transfer of positive charge from the cloud to the ground
 * Less than 5% of all strikes
 * Electric field is typically much stronger because it must burn through more air to reach the ground
 * Its flash duration in longer, and its peak charge and potential can be ten times greater than a negative strike (as much as 300,000 amperes and one billion volts)
 * can strike as much as 10 miles away creating forest fires and power line damage
 * more lethal and more damage
 * dominant type of cloud to ground strikes in the winter months
 * usually consists of one stroke (as opposed to two or more with negative lightning)

37. Mesoscale Convective Complexes: seasonality, geographic distribution, severity
 * A mesoscale convective complex by definition (based on analysis of enhanced IR satellite imagery):**
 * **Size:**
 * A. continuous cold cloud shield with IR temperature of less than or equal to -32◦C must have an area greater than or equal to 100,000 square km**
 * B. interior cold cloud region with temperature of less than or equal to -52◦C must have and area greater than or equal to 50,000 square km**
 * **Initiate – size definitions A and B are first satisfied**
 * **Duration – Continuous cold cloud shield (IR temp. less than or equal to -32◦C) reaches maximum size**
 * **Shape – minor axis/major axis of greater than or equal to 0.7 at time of maximum extent**
 * **Terminate – size definitions A and B no longer satisfied**


 * MCCs are typically warm-season events with over 86 % of the total 527 events occurring over the months of May, June, July, and August. MCC frequency peaks in April for the southeastern U.S. The Great Plains experience the most MCCs during the warm season with MCC precipitation percentages between 2% and 18%. The Southeast experiences the most MCCs during the Spring season (primarily April) with MCC precipitation percentages across much of the deep South between 2% and 10%. On average, the Southeast receives 0 to 4% of its annual precipitation from MCCs while most of the Great Plains receive double these values. Warm-season precipitation totals are highly dependent upon MCC precipitation across much of the southeastern agricultural centers (e.g., Mississippi River floodplain). The low-level jet at 850mb helps to initiate an MCC.**
 * JI (p. 130 Lutgens)**

38. Derechoes: types, seasonality, geographic distribution, severity
 * Occasionally, a squall line forms a bulge 50-200 miles wide producing what is called a derecho. These storms last several hours and can produce a swath of 100 mph winds and hail in an area as large as a state. Derecho’s are most common in the Midwest states and are rare south of 32 degrees N latitude. Derecho's are a class of MCC and are most common in the summer months and early spring. (pg 130 in the weather forecasting handbook) **
 * BW **

39. Winter Precipitation: forecasting process, importance of column thickness
 * Would like to add: **
 * Types of derechos: **
 * Serial - produced by multiple bow echoes embedded in a squall line, several hundred miles in length, associated with a strong, migrating low pressure system, found in the warm sector of a mid-latitude cyclone, cool season event (September-April) **
 * Progressive - Characterized by a single bow-shaped system which propagates north and parallel to an east-west boundary, warm season event (May-August) **
 * Hybrid - Combination of serial and progressive, may exhibit a zonal pattern or combo of trough/ridge patterns, no particular seasonal distribution **
 * KMS **
 * I would like to add:**
 * Derechoes**
 * **a widespread and long-lived windstorm associated with a band of rapidly moving showers and thunderstorms**
 * **tend to develop with westerly or northwesterly flow aloft (850 -500mb)**
 * **form along or north of east-west surface boundaries and propagate parallel to the boundary (the front provides uplift n moisture)**
 * **form where 850mb dew points are the highest (contributes moisture to storm): produces the elevated convection (high LCL’s (Lifted Condensation Level)) which can lead to downbursts**
 * **as they move, they migrate toward areas with high CAPE (south of boundary)**
 * **they will continue as long as sufficient CAPE is available and the shear is strong**
 * **there is a lower/mid-level dry area which fosters evaporative cooling and the further downward motion**
 * **there may be strong mid-level winds in place which can augment the RIJ (Rear Inflow Jet)**
 * **tend to form in environments where LI < -6 (LI – Lifted Index)**
 * **81% produced tornadoes (92%) were F2 or less**
 * **speed of winds may be augmented by low density, high relative humidity air near surface**
 * Criteria for Derechoes**
 * **produces straight line wind damage or gusts greater than 50 knots over an area with a major axis of at least 250mi**
 * **must be at least 3 reports of F1 damage and/or wind gusts of 65 knots or greater separated by at least 40mi (shows it’s not isolated, continuous)**
 * **no more than 3 hours can elapse between successive wind gust/damage reports**
 * seasonal distribution**
 * **cool season – more southerly states**
 * **warm season – towards the north**
 * **greatest incidence tend to follow the mean position of the jet stream which is the demarcation line between warm and cold air at the surface (i.e. frontal boundary)**
 * Serial Derecho**
 * **the strong, migrating low pressure system is often associated with 500mb through that is upstream of a mid-latitude cyclone**
 * **to the east of the trough, there is divergence aloft and low pressure at the surface**
 * **often found in the left exit region of a jet streak**
 * Progressive Derechoes**
 * **an upstream ridge is present for these events**
 * **often found in or near the right entrance region of a jet streak**
 * JI (p. 130 Lutgens)**


 * SLEET - Partially melted snow flakes that refreeze into pellets of ice before reaching the ground; Range in appearance from nearly clear to milky white depending on the amount of melting that occurred before refreezing; Not correct to think of sleet simply as raindrops that freeze before reaching the ground**


 * Freezing Rain - Freezing rain occurs when supercooled raindrops (typically from the complete melting of snowflakes) freeze on contact with a surface (roads, power lines, car windshields etc.); Two scenarios that cause freezing rain: 1) a shallow layer of cold air undercuts a warm air mass 2) warm air advects in aloft over cold air at the surface**


 * Freezing Drizzle - Freezing drizzle can occur with a sounding that is entirely below freezing; droplets remain supercooled due to a lack of ice crystals/nuclei to freeze on; the nuclei for ice crystals typically do not activate until the temperature is -10 degrees C or colder (though some nuclei can be activated at temperatures a few degrees warmer; Ideal temperatures for the growth of dendritic crystals is between -12 and -18 degrees C**


 * Forecasting Techniques**
 * 1000 to 500mb: 5400m = rain**
 * 1000 to 700mb: 2480 = rain**


 * 850 to 700mb warm air aloft? – sleet vs. freezing rain; 1500 to 4500ft may support sleet or freezing rain**
 * 1000 to 850mb thickness – rain vs. snow; if warm layer at surface is <900feet – snow, >1200ft – rain**
 * How warm is the elevated warm layer? if maximum temperature exceeds 3 to 4º C, snow will melt completely; if Tmax is less than 1º C, only partial melting occurs and snow will usually refreeze; Tmax from 1 to 3º C results in partial melting of the snowflake which will refreeze into sleet (or a mixture of sleet and freezing rain, depending on the depth of the warm layer)**


 * Deposition – the process of ice crystal growth through the direct transformation of water vapor to solid; it works best b/t -12 and -15 degrees C**
 * Evaporation in winter – lowers the T of the atmosphere when precipitation falls into a dry layer; may lead to a threat of winter weather where there was none previously; will help to lower the air T to the wet bulb T**


 * blizzards – winds may exceed 35mph w/ snow or blowing snow, reducing visibility to less than ¼ of a mile for at least 3 hours**

JI (p. 144 in Lutgens)
 * Avalanche – it can travel at speeds up to 200mph; 90% occur w/in 24 hours of snowfall; 80% are triggered by rapid accumulation of snowfall**