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Soundings and Adiabatic Diagrams for Severe Weather Prediction and Analysis Continued. Shear vs. CAPE. Need a balance between Shear and CAPE for supercell development Without shear: single, ordinary, airmass thunderstorm which lasts 20 minutes

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Soundings and adiabatic diagrams for severe weather prediction and analysis continued

Soundings and Adiabatic Diagrams for Severe Weather Prediction and Analysis Continued


Shear vs cape
Shear vs. CAPE Prediction and Analysis Continued

  • Need a balance between Shear and CAPE for supercell development

  • Without shear: single, ordinary, airmass thunderstorm which lasts 20 minutes

  • If shear is too strong (gust front moves too fast) : multicellular t-storms or low topped severe thunderstorms


Cape and shear
CAPE and Shear Prediction and Analysis Continued


Bulk richardson number
Bulk Richardson Number Prediction and Analysis Continued

BRN = CAPE

½ (Uz2)

Where Uz = the vertical wind shear

(averaged over 3-6km layer)

  • In general: 15-40 favors supercell development

    >40 favors multicellular type storms

  • Explains the balance between wind shear and convective energy


Bulk richardson number brn
Bulk Richardson Number (BRN) Prediction and Analysis Continued

BRN= CAPE

1/2Uz2

(where Uz is a measure of the vertical

wind shear)


Shear classification
Shear Classification: Prediction and Analysis Continued

  • Two Main types: Speed and Directional

  • Bulk Shear: The Boundary Layer through 6 km (or higher) above ground level shear vector denotes the change in wind throughout this height.

  • Usually given in units of knots

  • Thunderstorms tend to become more organized and persistent as vertical shear increases. Supercells are commonly associated with vertical shear values of 35-40 knots and greater through this depth

  • Doesn’t take into account elevated parcels:

  • Effective Shear (kts)

  • Bulk Richardson Number shear (m^2/s^2)


Directional shear
DIRECTIONAL SHEAR Prediction and Analysis Continued

  • Veering vs. Backing winds with height

  • Clockwise vs. Counterclockwise with height

  • Warm Air advection vs. Cold Air Advection

  • Northern vs. Southern Hemisphere


Shear just right
Shear Just Right Prediction and Analysis Continued

  • 2-D equilibrium: squall line develops

  • 3-D equilibrium: right moving and left moving supercells

A

B

A

B

L

Left Mover

L

Right Mover


Hodographs

V Prediction and Analysis Continued

Hodographs

North

  • Draw wind vectors in direction they are going

  • This is opposite of how the wind barbs are drawn

U

West

East

Wind speed

South


How a hodograph is created
How a Hodograph is Created! Prediction and Analysis Continued

  • Lets open our Sounding COMET Module…


Example
Example Prediction and Analysis Continued


Straight line shear

Storm Splitting: Prediction and Analysis Continued

R and L storm cells move with mean wind but drift outward

Straight Line Shear

500

700

850

900

1000


Curved hodograph
Curved Hodograph Prediction and Analysis Continued

  • Emphasizes one of the supercells

    • Veering (clockwise curve):

      • right moving supercells

      • warm air advection in northern hemisphere

    • Backing (counter clockwise curve):

      • left moving supercells

      • warm air advection in southern hemisphere

700

300

500

850

900

1000


Straight Line Hodograph Prediction and Analysis Continued

Clockwise Curved hodograph


Helicity

Can be thought of as a measure of the “corkscrew” nature of the winds.

Higher helicity values relate to a curved hodograph.

large positive values--> emphasize right cell

large negative values--> emphasize left cells

Values near zero relate to a straight line hodograph.

Helicity

H = velocity dotted with vorticity

= V • ζ

= u (dyw - dzv) - v (dxw - dzu) + w (dxv - dyu)


Lets review main points
Lets Review Main Points of the winds.

  • Shear in two parts: Direction and Speed

  • Hodographs: characterize shear and help us to visualize the vertical shear profile

  • Helicity = V • ζ

  • Positive values favor right cells

  • Negative values favor left cells

  • 2-d equilibrium calls for developing squall line

  • 3-d equilibrium calls for storm splitting to occur.

  • Now lets take a look at some radar loops to see these processes in action!!!!


The granddaddy of them all not the rose bowl
The “Granddaddy” of them all!!! of the winds.Not the Rose Bowl

  • Super Tornado Outbreak of March 11th- 12th , 2006

  • Early season event, Strongly dynamically driven

  • 105 confirmed tornadoes, 13 fatalities

  • Longest lived singular supercell in recorded weather history!

  • Supercell tracked 800 miles across Oklahoma, Kansas, Missouri, Illinois, Indiana, and Michigan.

  • Supercell lasted 17.5 hours

  • Accounted for nearly a 1/3 of the tornadoes on March 12th!

  • In a few weeks we will cover the physical and dynamical processes involved in creating and maintaining a supercell through its complete life-cycle.


Cape and helicity
CAPE and Helicity of the winds.

  • Plainfield, IL tornado:

  • CAPE=7000

  • Helicity=165

  • Energy Helicity:


In class case study tornado outbreak missouri illinois indiana

In Class Case Study of the winds.Tornado OutbreakMissouri, Illinois, Indiana

3/08/09


Synoptic setup 300mb
Synoptic Setup: of the winds.300mb


500mb
500mb of the winds.


700mb
700mb of the winds.


850mb
850mb of the winds.


925mb
925mb of the winds.


Surface
Surface of the winds.


Springfield missouri
Springfield, Missouri of the winds.


Lincoln illinois
Lincoln, Illinois of the winds.





Radar loops http vortex plymouth edu nids html
Radar Loops of the winds.http://vortex.plymouth.edu/nids.html


Radar loops http vortex plymouth edu nids html1
Radar Loops of the winds.http://vortex.plymouth.edu/nids.html


What to take away from this event
What to take away from this event…? of the winds.

Dynamics/Shear dominate heat energy!

  • Strong mid/upper level shortwave trough

  • Strong dynamical forcing/frontal forcing

  • Strengthening surface low

  • Cold temperatures: <70F

  • Very small CAPE values: <1000J/kg

  • Bulk Shear: 80+ kts !!!

  • Helicity: 500+ m^2/s^2 !!!

  • Clockwise Hodographs favoring right moving cells

  • Perfect situation for low topped discrete supercells capable of producing tornadoes near triple point.


Stability indices

Stability Indices of the winds.


K index
K Index of the winds.

  • This index uses the values for temperature (t) and dew point temperature (td), both in oC at several standard levels.

    K = t850 - t 500 + td850 - t700 + td700


Vertical totals
Vertical Totals of the winds.

VT = T850 - T500

  • A value of 26 or greater is usually indicative of thunderstorm potential.


Cross totals
Cross Totals of the winds.

CT =T d850 - T500


Total totals tt
Total Totals (TT) of the winds.

TT = VT + CT

=T850 + T d850 - 2 T500


Sweat severe weather threat index
SWEAT (severe weather threat) Index of the winds.

SWI = 12D + 20(T - 49) + 2f8 + f5 + 125(S + 0.2)

where: D=850mb dew point temperature (oC)

(if D<0 then set D = 0)

T = total totals (if T < 49 then set entire term = 0)

f8=speed of 850mb winds (knots)

f5= speed of 500mb winds (knots)

S = sin (500mb-850mb wind direction)

And set the term 125(S+0.2) = 0 when any of the following are not true

  • 850mb wind direction is between 130-250

  • 500mb wind direction is between 210-310

  • 500mb wind direction minus 850mb wind direction is positive

  • 850mb and 500mb wind speeds > 15knots


Sweat severe weather threat index1
SWEAT (severe weather threat) Index of the winds.

SWI = 12D + 20(T - 49) + 2f8 + f5 + 125(S + 0.2)


Lifted index li
Lifted Index (LI) of the winds.

  • Compares the parcel with the environment at 500mb.

    LI = (Tenv-Tparcel)500


  • Best Lifted Index of the winds.

    • Uses the highest value of qe or qwin the lower troposphere.

    • Use the highest mixing ratio value in combination with the warmest temperature.

  • SELS Lifted Index

    • Use the mean mixing ratio and mean q of the lowest 100mb

    • If using a 12z sounding add 2o

    • Start parcel at 50mb above the surface


Showalter index si
Showalter Index (SI) of the winds.

  • Compares a parcel starting at 850mb with the environment at 500mb.

    SI = (Tenv-Tparcel)500


Supercell index
Supercell Index of the winds.

  • Weights various parameters which are indicative of possible supercell development


Important points to remember
Important Points to Remember of the winds.

  • Severe weather is more dependent on dynamical forcing than instability!

  • No one parameter tells the full tale!

  • 12z soundings usually predict afternoon convection better than 00z soundings predict evening convection.


Links
Links of the winds.

  • http://www.geocities.com/weatherguyry/swx2.html

  • http://avc.comm.nsdlib.org/cgi-bin/wiki.pl?Severe_Weather_Indices

  • http://www.theweatherprediction.com/severe/indices/

  • http://www.theweatherprediction.com/habyhints/315/

  • http://www.spc.noaa.gov/exper/mesoanalysis/

  • http://mocha.meteor.wisc.edu/table.12z.html


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