1. COMET ® Teletraining Forecasting Severe Thunderstorms Version 1.0 Dr. Douglas Wesley UCAR/COMET Ms. Wendy Schreiber-Abshire UCAR/COMET Tuesday, 9 June 1998 © 1998 University Corporation for Atmospheric Research. All Rights Reserved 1

2. Forecasting Severe Thunderstorms Main Menu Introduction and Objectives (Page 3) Section 1: Assessing Environmental Stability (Page 4) Section 2: Assessing Environmental Shear (Page 15) Section 3: Forecasting Supercells (Page 25) Section 4: Forecasting Mesoscale Convective Systems (Page 30) Summary, Quiz, and Evaluation (Page 35) 2

3. Introduction and Overall Objectives of the Teletraining Session Describe the roles of environmental stability and wind shear in the development of severe thunderstorms Describe important enviromental factors contributing to the development of rotating updrafts in thunderstorms Distinguish between the different storm types and severe weather associated with them Describe the formation and typical environments for supercells 3

4. Introduction (cont.) Emphasis of this teletraining session will be on these basic convective processes: buoyancy, gust front, and dynamic interactions

5. Section 1:Assessing Environmental Stability By the end of this section, you should be able to Identify important buoyancy processes that contribute to updraft strength Describe the impact on thunderstorm potential for buoyancy processes Describe the role of surface heating in enhancing buoyant energy 5

6. Moore: 3 Lapse rates

7. Moore: pos/neg areas

9. Moore p. 8: 3 soundings; no instab., neutral, unstable

11. CAPE/LI values and associated degree of instability CAPELI (J/kg)(500 mb) Stable:0>0 marginally unstable<10000 to -3 moderately unstable1000-2500-3 to -6 very unstable2500-3500-6 to -9 extremely unstable>3500<-9

12. Moore p. 4: Conditional instability; lifting a layer

13. Moore p. 30: dry microburst sounding

14. Moore p. 36: wet microburst sounding

15. Moore p. 37: effect of elevated terrain on sounding

16. Non-supercell rotating updraft conceptual model

17. Summary: Assessing Environmental Stability Neutral, stable and unstable lapse rates Definitions of CAPE/CIN Modification of soundings by heating, terrain, layer lift Dry and wet microbursts, non-supercell rotation

18. Section 2:Assessing Environmental Shear By the end of this section, you should be able to Identify important wind shear processes that affect thunderstorm evolution Describe the role of directional shear in the evolution of strong convective cells 18

19. The Role of Wind Shear Get bullets from Anticipating (Wendy?) see Moore p. 58

20. Moore p. 43: on synoptic scale, shear in various zones around fronts

27. Importance of pre-severe convective storm hodograph Strong backing of winds with height in the lower troposphere favors development of left-moving anticyclonically rotating storms strong veering of winds with height in the lower troposphere favors development of right-moving cyclonically rotating storms wind profile with shear but little/no veering

28. Hodograph (cont.) or backing favors splitting storms where the right-moving cyclonically rotating cell is usually more severe warm air advection or low-level jets can increase clockwise turning

29. Note: need the flc here

32. Summary: Assessing Environmental Shear 32

33. Section 3:Forecasting Supercells By the end of this section, you should be able to Identify important buoyancy processes that contribute to supercell formation Describe the impact of wind shear on supercell potential 33

34. Hodographs and Supercells Tornado proximity soundings show considerable clockwise turning in the lowest 1.5 km AGL with little curvature above that; speeds increasing with height, esp. in the first few km wind speeds (both ground and storm- relative) and rightward propagation increase significantly with tornado intensity

36. This page intentionally left blank (The notes page for this slide contains the first set of definitions to be completed by the learners as part of the exercise.) 36

37. This page intentionally left blank (The notes page for this slide contains the second set of definitions to be completed by the learners as part of the exercise.) 37

38. Frequency of Severity Reports 38

39. Exercise 2 Map 39

40. Summary: Icing Type and Severity Icing can be categorized into rime, clear, mixed and SLD types In general, rime icing tends to occur with T -10° C, and mixed ice at temperatures in between. However, type varies depending on LWC, droplet size, and aircraft-specific variables Severity is categorized by the rate of accumulation, the effectiveness of available de-icing equipment, and the actions a pilot must take to avoid or combat icing Algorithms and numerical model output have been developed to correlate values of LWC, temperature, and droplet size with icing type and severity. These algorithms and model output are in the early stages of development and need further testing 40

41. Section 4: Supercooled Large Drops (SLD) By the end of this section you should be able to Describe two atmospheric processes and environments that support SLD formation Describe cloud-top conditions most favorable to SLD formation Identify favorable areas and layers for SLD formation using skew-T diagrams, wind profiles, surface precipitation observations, and 3.9 micron infrared satellite imagery 41

42. Schematics Of Airflow Around An Iced Airfoil In An SLD Situation 42

43. Quiz and Evaluation At this time, please complete the separate quiz. You may do so anonymously. Also, please complete the evaluation form for this teletraining session. This information will help us to improve future sessions. Please give your completed quiz to your site facilitator, who in turn should mail them to: Post:orFedEx:Dwight OwensUCAR/COMET P.O. Box 3000 3450 Mitchell Lane Boulder, CO 80307-3000Boulder, CO 80301 (303) 497-8469 43

44. Forecasting Aircraft Icing: Acknowledgements Graphics from American Meteorological Society (AMS) modified from –Bernstein (1997) –Kane, et al. (1998) –Martner, et al. (1993) –Politovich, Stankov, and Martner (1996) –Rasmussen, et al. (1993) –Sand, et al. (1984) –Schultz & Politovich (1992) –Willoughby and Protrowicz (1984) Additional images from –NASA-Lewis Research Center –NOAA/NWS –Omeron-Bernstein (1997) unpublished 44