Date post: | 01-Apr-2015 |
Category: |
Documents |
Upload: | jaylan-weight |
View: | 212 times |
Download: | 0 times |
COMET® TeletrainingForecasting 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
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
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
Introduction (cont.)
Emphasis of this teletraining session will be on these basic convective
processes: buoyancy, gust front, and dynamic interactions
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
Moore: 3 Lapse rates
Moore: pos/neg areas
Skwtcape.flc
Moore p. 8: 3 soundings; no instab., neutral, unstable
Cincape3.flc
CAPE/LI values and associateddegree of instability
CAPE LI(J/kg) (500 mb)
Stable: 0 >0marginally unstable <1000 0 to -3moderately unstable 1000-2500 -3 to -6very unstable 2500-3500 -6 to -9extremely unstable >3500 <-9
Moore p. 4: Conditional instability; lifting a layer
Moore p. 30: dry microburst sounding
Moore p. 36: wet microburst sounding
Moore p. 37: effect of elevated terrain on sounding
Non-supercell rotating updraft conceptual model
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
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
The Role of Wind Shear
• Get bullets from Anticipating (Wendy?)
• see Moore p. 58
Moore p. 43: on synoptic scale, shear in various zones around fronts
Hodott02.flc
Hodott03.flc
Johnspat.gif
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
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
2dsqldev.gif
Note: need the flc here
Tiltvort.flc
Splitsqa.flc
Summary: Assessing Environmental Shear
32
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
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
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
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
Frequency of Severity Reports
38
Exercise 2 Map
39
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 <-15° C, clear
when 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 testing40
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
Schematics Of Airflow Around An Iced Airfoil In An SLD Situation
42
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: or FedEx:Dwight Owens Dwight OwensUCAR/COMET UCAR/COMETP.O. Box 3000 3450 Mitchell
Lane Boulder, CO 80307-3000 Boulder, CO
80301(303) 497-8469
43
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) unpublished44