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1-3 day forecast for thunderstorms via Showalter & Jetstream







Source: Weather.unisys


Showalter map bottom right = white lines with values in wet bulb potential temperatures (deg C).
Jetstream map upper right = speed values in color (m/s) + direction via arrows at 300 hPa.


Critical values for Showalter Index: (not to be used with frontal inversion between 850-500 hPa)

< +3: showers, possible thundery.
<  -2: severe thundersorms.
<  -5: risk for tornados.

Jetstream (= windspeed > 60 kt (31 m/s)).
Left exit & right entrance regions bring upwards motion enhancing development of showers or thunderstorms.
Right exit & left entrance regions bring downwards motion weakening development of showers.

A little explanation where to find these zones:

Jet streaks pull in air upstream (to their west) in what is called the entrance region and throw it out downstream (to their east) in what is called exit region. They are further subdivided in a left or right zone as shown on the picture.



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