1. ORIGINAL PRESENTATION – 11 MAR 2010 NBGSA CONFERENCE – SAN DIEGO UPDATED – 5 APR 2013 WWW.ROUTE283EAST.COM THIS IS A SAMPLE PRESENTATION KINEMATIC STRUCTURE AND FEATURES OF A COOL-SEASON BOW ECHO

2. Table of Contents Intro System Setup Storm Overview Kinematic Structure Findings Conclusions

3. Bow Echo Characteristics 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 Echo near Tuscaloosa, AL

4. Bow Echoes: Structure & Features Strong mid-level winds move through cold dry air at 3-7 km AGL (Johns 1993) When they encounter main downdraft, storm is strengthened at surface through increased evaporation and vertical momentum transport (Weisman 2001) Combines with the downdraft outflow (gust front) to accelerate system, cause the bowing of line (Smull & Houze 1987b) Behind the apex is the Rear Inflow Jet (RIJ) (Przybylinski 1983) Bookend vorticies flank and amplify the RIJ (Weisman 1990) Long-lived bow echoes can become derechoes (Heinrich 1888) Bow Echo evolution, from Fujita (1978); note “Bookend Vorticies”

5. 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.

6. 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

7. 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: Cool-Season Severe Weather Severe Weather in the Southeast US Damaging windstorms in the Southeast US

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