1 / 45

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. Need a balance between Shear and CAPE for supercell development Without shear: single, ordinary, airmass thunderstorm which lasts 20 minutes

rigg
Download Presentation

Soundings and Adiabatic Diagrams for Severe Weather Prediction and Analysis Continued

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Soundings and Adiabatic Diagrams for Severe Weather Prediction and Analysis Continued

  2. Shear vs. CAPE • 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: multicellular t-storms (gust front moves too fast)

  3. Shear Classification: • Two Main types: Directional and Speed • 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)

  4. CAPE and Shear

  5. Shear Just Right • 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

  6. Bulk Richardson Number 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

  7. Bulk Richardson Number (BRN) BRN= CAPE 1/2Uz2 (where Uz is a measure of the vertical wind shear)

  8. V South Hodographs • Draw wind vectors in direction they are going • This is opposite of how the wind barbs are drawn U East West Wind speed North

  9. Example

  10. Storm Splitting: R and L storm cells move with mean wind but drift outward Straight Line Shear 500 700 850 900 1000

  11. Curved Hodograph • 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

  12. Straight Line Hodograph Curved hodograph

  13. 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)

  14. CAPE and Helicity • Plainfield, IL tornado: • CAPE=7000 • Helicity=165 • Energy Helicity:

  15. Tornado OutbreakMissouri, Illinois, Indiana 3/08/09

  16. Synoptic Setup:300mb

  17. 500mb

  18. 700mb

  19. 850mb

  20. 925mb

  21. Surface

  22. SPC really jumps on the bandwagon…Yee Haw!!!

  23. SPC really jumps on the bandwagon…Yee Haw!!!

  24. Springfield, Missouri

  25. Lincoln, Illinois

  26. 1600z SPC Mesocale Discussion

  27. Radar Loopshttp://vortex.plymouth.edu/nids.html

  28. Radar Loopshttp://vortex.plymouth.edu/nids.html

  29. What to take away from this event…? 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.

  30. Stability Indices

  31. K Index • 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

  32. Vertical Totals VT = T850 - T500 • A value of 26 or greater is usually indicative of thunderstorm potential.

  33. Cross Totals CT =T d850 - T500

  34. Total Totals (TT) TT = VT + CT =T850 + T d850 - 2 T500

  35. SWEAT (severe weather threat) Index 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

  36. SWEAT (severe weather threat) Index SWI = 12D + 20(T - 49) + 2f8 + f5 + 125(S + 0.2)

  37. Lifted Index (LI) • Compares the parcel with the environment at 500mb. LI = (Tenv-Tparcel)500

  38. Best Lifted Index • 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

  39. Showalter Index (SI) • Compares a parcel starting at 850mb with the environment at 500mb. SI = (Tenv-Tparcel)500

  40. Supercell Index • Weights various parameters which are indicative of possible supercell development

  41. Important Points to Remember • 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.

  42. Links • 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

More Related