Thunderstorm: Variables & Ingredients

Ø  Variables needed for Severe thunderstorms:

1.    Moisture

2.    Instability

3.    Lift

4.    Wind shear

Ø  Bob, from Texas

̶        Launches weather balloons (radiosonde)

̶        Radioing back temperature, dewpoint, etc…

̶        Thermodynamic diagrams

Ø  Wind shear

1.    Speed Shear

o   Winds increasing speed with height

2.    Directional Shear

o   Winds changing direction with height

Ø  Development

̶        Cumulus Humilius

̶        Cumulus Congestus

̶        Towering Cumulus – not precipitating

̶        Cumulonimbus (Cb) – precipitating

Ø  Texture

̶        More “cauliflower” the stronger the updraft

̶        “rock hard towers” implies that most of the cloud is in the liquid phase

̶        Updraft liquid weakens or reaches high in the troposphere = liquid freezes = giving cloud a “glaciated” texture (considered fairly weak)

Ø  Anvil

̶        Crisp

̶        Fuzzy

Ø  Vertical Shear

̶        Increases longevity and organization

̶        Strong shear = storm-scale rotation by tilting horizontal vorticity into vertical vorticity

̶        Too much shear = the storm cannot organize (“orphan anvils”) = CAPE is too weak and shear is too strong

Ø  Flanking Line

̶        Flanking line leading into the main updraft

̶        Main cell SW is tilted due to the environment shear

Ø  Boundaries (pg. 307)

̶        Describes fronts

̶        The leading edge of thunderstorm outflow

̶        Leading edge of the sea breeze

̶        Any other lines marking the junction of 2 airmasses

Ø  Creating Boundaries

̶        Differential heating of air either over surfaces with different properties, such as water, and lands, forests and fields, urban and rural landscapes, or over surfaces heated differently  (land over cloudy versus clear skies)

Ø  Occlusion = Cold air rapping around a cove

Ø  WER = Not a lot of precipitation/ at all

Ø  Anvil à Sinus Cloud à Made from ice crystals

Ø  More evaporation = High LCL’s = Relative humidity is lower towards the ground

Ø  LCL = Helps indicate the relative humidity of the sub-cloud layer

Ø  Wet Bulb Zero = Sleet = Frozen Rain

Ø  Verga = Rain that evaporate before hitting the ground

Ø  BRN (Bulk Richardson’s Number): CAPE is too weak and the shear is too strong

̶        Sweet spot: 10-45 BRN

                 BRN = CAPE / Shear

Ø  What 3 influences does dry air have on severe weather? 

̶        More evaporation = Stronger downdraft

̶        Dryer air in Mid-level of atmosphere tends to promote large hail growth

̶        Connectivity unstable (will learn in unit 2)

Ø  Single Cell Thunderstorms

̶        Single cell storms are dominated by buoyancy processes

̶        Sometimes called “air mass” t-storms, these storms are poorly organized and pose relatively little threat to the public (lightning and hail)

̶        Typical of afternoon thunderstorms

̶        Updrafts form in relatively random locations

̶        The dominant forcing feature is instability since they form in a low-shear

̶        Goes through the cycle within 30-60mins

̶        Severe weather threats minimal

̶        Pulse Severe Storm

Ø  Severe single cell thunderstorm

̶        Forms in a low shear environment

̶        Taller updraft/More instability

̶        More intense reflectivity/More intense core

̶        Longer lasting

̶        Precipitation takes longer to descend to the ground/Stronger updraft

̶        Vertical Integrated Liquid (VIL) is larger

̶        “Popcorn Severe”

Ø  What are the differences with ordinary thunderstorm and a “pulse” severe thunderstorm?

1.    Taller updraft/More instability

2.    More intense reflectivity/More intense core

3.    Longer lasting

4.    Precipitation takes longer to descend to the ground/Stronger updraft

̶        Both form in a low shear environment

Ø  Land Spouts

̶        Single cell thunderstorm can create them

̶        Horizontal shear causing vertical vorticity that stretches and causes a tornado

̶        Tend to have a double vortex (thin core and translucent on the outside)

̶        Usually weak, not always