Another bout of severe storms possible tonight

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A return of higher dew points today will increase the threat for strong thunderstorms in northern and western Minnesota tonight. The Storm Prediction Center has shaded an area of the Dakotas and parts of Minnesota with the best potential for damaging winds and large hail.

Prior to the storms it will be a warm Holiday with temperatures this afternoon well into the 80s. Here’s a graphic from Duluth NWS of the maximum temperature forecasts for the Lake’s region.

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In case you missed it, last Friday the temperature surged to 99 degrees at the Twin Cities International Airport late in the afternoon. This fell one degree shy of the record high for July 1st of 100 degrees set in 1883. Dew points in the middle 70s resulted in Heat Index values (feels-like temperature) of 105 degrees.

The conditions were very ripe for damaging thunderstorms on July 1st. A large swath of Minnesota and western Wisconsin experienced some wind damage. A storm survey was done by the staff of the Duluth Office on the storms in Burnett County Wisconsin. Here is a summary of the damage and a nice photo of a shelf cloud. Storm reports for the events on Friday can be seen by clicking on the SPC storm report.

You’ll recall that July 4th 1999 was the date of the Boundary Water Canoe Area blow down with the derecho that moved from the Dakotas across northern Minnesota and Lake Superior. This event resulted in a long period of recovery and controlled burns to make the region safe for recreationalist. A derecho is a long lived severe weather event of strong to destructive straightline winds that can exceed 100 miles an hour.

Here’s the definition of a bow echo, which was observed on radar on Friday afternoon and evening. A bow echo is associated with squall lines or lines of convective thunderstorms. These echoes can range in size from 20 to 200 km, and have a life span of 3 to 6 hours. Bow echoes tend to develop when moderate to strong wind shear exists in the lower 2 to 3 km of the atmosphere. While similar to squall lines, bow echoes are smaller in scale; and are moved by the wind inside them. They tend to push outward and after time die out.

Damage was also considerable in southwest Minnesota. Here’s a summary of the damage, with radar imagery posted by the Chanhassen NWS Office from the July 1st storms.

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The forecast UV index for the Nation is high on this Fourth of July. If you avoided a sun burn so far, be cautious today. You can damage your skin in less than an hour with a UV index in the seven or above category.

We did a little experiment at Target Field in the heat of the afternoon on Sunday. The shade temperature at 3PM was 85 degrees. We placed a thermometer in the direct sun and it climbed all the way to 101 degrees. The official temperature is reported in the shade.

Stay tuned later today for the potential for strong storms.

CE

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