Saturday, August 7, 2010

Tornado Watch until 1 am (includes Twin Cities)

Update: 6:40 pm. Tornadic circulation showing up southwest of Fergus Falls. GR2 Analyst software shows very strong rotation markers - possibly reaching the ground, just southeast of Breckenridge, moving toward Fergus Falls - possibly holding together into the Alexandria area within the next hour. Tornado warnings are in effect based on rotation - no confirmation of touchdowns (yet), but central MN is under a tornado watch until 1 am - includes the Twin Cities metro area.

Update: 6:30 pm. Tornado Warning for parts of Grant, Otter Tail and Wilkin counties of west central MN until 7 pm. Doppler showing a developing "couplet" (meaning strong rotation) - a supercell capable of spinning up a tornado. the greatest risk is from Wahpeton and Wheaton to Elbow Lake and Fergus Falls. (This Doppler Radar image shows SRV or "storm relative velocity", showing air moving toward and away from the Doppler Radar site in Grand Forks, ND).

Tornado Watch until 1 am. SPC has a big chunk of Minnesota in a tornado watch until 1 am, meaning conditions are ripe for isolated tornadoes. We have all the ingredients - a warm frontal boundary, juicy low-level moisture (dew points in the 70s), sufficient wind shear and instability aloft for a few "supercell" thunderstorms capable of large hail and a few tornadoes.

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