Severe Weather What creates it, what it means, and how to stay safe

Table of Contents Overview Heavy Rain & Floods High Winds (Bow Echoes & Derechoes) Lightning Hail Tornadoes Hurricanes and Tropical Storms Weather threats Watches and Warnings

High winds Strong winds above the ground are drawn downward within the storm This helps to create a “gust front” and causes the storm to accelerate and “bow out” Winds create a feedback system with a main flow behind storm (“rear inflow jet”) and rotation on the ends (“bookend vorticies”).

Tornadoes: Distribution vs. Deaths Most US tornadoes occur in “tornado alley” (TX, OK, KS) But the frequency of killer tornado events in highest in the southeast (AR, TN, MS, AL)

A warning on statistics BE CAREFUL WITH AVERAGES! ◦One year of data can strongly skew averages  Hurricane fatalities ◦ 2005: 1016 fatalities ◦ , : 123 fatalities (14 per year) ◦ 10-year avg: 114 fatalities per year  Tornado fatalities ◦ 2011: 553 fatalities ◦ : 522 fatalities (58 per year) ◦ 10-year avg: 108 fatalities per year ◦It is generally safer to use averages over longer periods  But shorter average times have uses as well

Watches and Warnings Weather watch ◦Conditions are “favorable” for development ◦i.e. it COULD happen ◦E.g. a strong cold front moving into warm, moist air creates the chance for strong thunderstorms, so a Severe Thunderstorm Watch may be issued Weather warning ◦The weather event is HAPPENING or is IMMINENT ◦E.g. authorities have spotted a tornado OR weather radar indicates strong rotation within a storm, so a Tornado Warning will be issued

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