1. Severe Thunderstorm Summary METR 361

2. The Pre-storm Environment On the Surface map, look for: On the Surface map, look for: 1.Warm air, T > 50 F 2.High dew points > 50 F 3.“Triggers” a. Cold front b. Dryline c. pressure trough d. Outflow boundaries

3. 850 mb map: Temperature Ridge Temperature Ridge Humidity Ridge Humidity Ridge Low level jet Low level jet

4. 700 mb map: Dry air (intrusion) for convective instability Dry air (intrusion) for convective instability

5. 500 mb: Cool air “pockets” Cool air “pockets” Difluent areas Difluent areas

6. 300 mb, 250 mb, 200 mb: Jets Jets Ageostrophic flow sets up cap Cap is broken when jet moves

7. Soundings T1 T1 Humid at low levels Dry above 700 mb Capping Inversion Indices (CAPE, LI, TT, SWEAT, etc Indices (CAPE, LI, TT, SWEAT, etc …

8. Composite Charts are very helpful to assess the areas of likely severe weather: By only plotting symbols of features favorable to severe trws, “clutter = severe By only plotting symbols of features favorable to severe trws, “clutter = severe

9. NWS Warning Procedure Convective outlook early in day (from SPC) Convective outlook early in day (from SPC) Not for public warning purposes Often seen on the Weather Channel.

10. Watches (from SPC) Watches (from SPC)Tornado Severe Thunderstorm

11. Warnings come from the local offices

12. Verification is done by local offices and reported to SPC and NCDC

13. For straight-line wind only, look for a. uni-directional shear (speed shear) a. uni-directional shear (speed shear) b. dry air to create downward momentum b. dry air to create downward momentum For large hail, look for a. large lapse rates in the hail growth zone a. large lapse rates in the hail growth zone b. Wet-bulb zero between 2200 and 2800 m b. Wet-bulb zero between 2200 and 2800 m (about 770 hPa to 720 hPa) For tornadoes, look for a. both speed and directional shear a. both speed and directional shear b. large lapse rates (CAPE) b. large lapse rates (CAPE) c. more ingredients to increase severity c. more ingredients to increase severity