Friday, May 8, 2009

Derecho, MCC Hammers Southern Missouri

A very large complex of thunderstorms has swept across southeast Kansas and into southern Missouri this morning.

It is currently moving into southeast Missouri and clipping extreme northern counties of Arkansas.

When you get a long-lived complex of thunderstorms like this, it is called an MCC, or meso-scale convective complex.

A meteorologist usually uses an infrared satellite to determine an MCC. They typically form at night and cover a large area.

MCC's bring heavy rain, a lot of lightning and wind, often hail and sometimes even tornadoes.

In today's case, this MCC has been dropping 3 inches of rain per hour on some locations in southeast Kansas.

Today's storm system moving across southern Missouri also is a derecho.

The origins of this word are Spanish and mean straight.

Check out the radar image just before 10 am local time below.

Notice the comma shape to the radar return, or backwards "C" shape, shown in red.

This is the leading edge of the thunderstorm complex that has bowed out and moved across dozens of counties for over 100 miles.

All along that comma shape there are very strong, straight-line winds at times in excess of 80 mph.

This is a textbook example of a derecho, which is a widespread and long-lived, violent straight-line windstorm that is associated with a fast-moving band of severe thunderstorms in the form of a squall line usually taking the form of a bow echo.

Portions of southern Missouri and northern Arkansas remain under a PDS Severe Thunderstorm Watch.

PDS means particularly dangerous situation.

Out ahead of this MCC a tornado watch has been issued for southeast Missouri, northeast Arkansas, southern Illinois and portions of western Tennessee and Kentucky.

Elsewhere around the nation the weather is active on a different note.

Record heat can be found from west Texas to the deserts of southern California and wildfires are still threatening many areas of the Santa Barbara, CA vicinity.

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