KINEMATIC STRUCTURE AND FEATURES
OF A COOL-SEASON BOW ECHO
ORIGINAL PRESENTATION – 11 MAR 2010
NBGSA CONFERENCE – SAN DIEGO
UPDATED – 5 APR 2013
WWW.ROUTE283EAST.COM
THIS IS A SAMPLE PRESENTATION
Table of Contents
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Intro
System Setup
Storm Overview
Kinematic Structure
Findings
Conclusions
Bow Echo Characteristics
Bow Echo near Tuscaloosa, AL
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Bow Echoes are specialized Convective Weather Systems
Identifiable by curving section of thunderstorms on radar
Presence of bow echo indicates strong winds at surface
Can be born from squall lines, supercells or cell merger
2 typical patterns: Warm Season (Great Plains/Great Lakes) &
Cool Season (Southeast/Atlantic Coast)
Bow Echoes: Structure & Features
Bow Echo evolution, from Fujita (1978); note “Bookend Vorticies”
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Strong mid-level winds move through cold dry air at 3-7 km AGL (Johns 1993)
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When they encounter main downdraft, storm is strengthened at surface through
increased evaporation and vertical momentum transport (Weisman 2001)
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Combines with the downdraft outflow (gust front) to accelerate system, cause the
bowing of line (Smull & Houze 1987b)
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Behind the apex is the Rear Inflow Jet (RIJ) (Przybylinski 1983)
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Bookend vorticies flank and amplify the RIJ (Weisman 1990)
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Long-lived bow echoes can become derechoes (Heinrich 1888)
Winds (U vs UR)
U-winds (east/west
winds) are primarily
from the west in the
strongest part of the
storm.
UR-winds: east/west
winds RELATIVE to
storm motion.
Stronger winds
embedded within
the storm flow.
Strong westerly
winds alternate with
weaker westerly
winds.
Mesovortices
• Storm motion, downdraft & RIJ account for much damage (especially at the bow apex)
• Mesovortices along the line can enhance surface wind along the line
• 9 March 2006 had one very strong mesovortex and other weaker ones
• Vortex will ENHANCE ambient flow
to the south and INHIBIT flow to the
north, possible that wind is STRONGER
than at apex
• POSITIVE vorticity
Take-Home Points
Squall lines can be as dangerous as more well known weather events (Tornadoes, etc)
Dangerous winds can be from a combination of storm features
Mesovortices are an important part of this storm’s dynamics
More research needs to be done in the areas of:
Comparison of Derecho Fatalities
Cool-Season Severe Weather
153
Severe Weather in the Southeast US
254
Derechoes
F0 & F1 Tornadoes
F2 Tornadoes
Damaging windstorms in the Southeast US
71
158
Hurricanes
Conclusion of sample presentation
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