Using new 3-D visualization software it's now possible to peer inside a severe thunderstorm. This next-generation Doppler radar software shows the outline of the storm; the red "hail core" shows up vividly, with evidence of strong winds immediately above the ground, causing the updraft to "sheer" or bend over at an angle. This new meteorological tool even shows strong areas of rotation in the mid levels of a "supercell" thunderstorm, usually a precursor to a tornado. Just as a doctor runs a Cat Scan and other tests before making a diagnosis, meteorologists use this 3-D weather Cat Scan to determine which thunderstorm (out of 30-60 on a given afternoon) may have the tell-tale signature of a spinning, potentially dangerous storm, called a "mesocyclone" or "supercell". Most common in tornado alley, from Texas to Iowa, these rotating storms are quite rare in Minnesota - it's estimated that 20-30% of these spinning storms go on to produce tornadoes.
This is the severe storm that formed over Benton County, near St. Cloud - the NWS issued a severe storm warning for 1"+ (nickel-size) hail. Remember that, on rare occasions, a tornado can develop, even during a generic severe thunderstorm warning. Don't wait for the sirens to sound to seek shelter. If skies turn green and menacing, and the cloud base begins to lower and rotate slowly, head for the basement, or a small, interior room. Large hail (ping pong ball size or larger) is a strong tip-off that a storm has an intense and potentially violent updraft. That's all a tornado is, a severe updraft with a focused circulation that reaches the ground.
* 72 degree high in the Twin Cities Wednesday before the storms mushroomed almost directly overhead.
* Thunderstorms weaken as they move into the metro area Wednesday, nothing severe reported, just some wind gusts to 35 mph.
* Today: last mild day in sight for some time, probably dry and thunder-free.
* Friday: growing chance of PM showers, wet start to the weekend.
* Saturday: Cooler, still breeze (take a hefty jacket), lot's of clouds, a few spotty showers far northern MN, especially PM hours.
* Sunday: better chance of spying the sun, 50s north, low 60s far southern lakes.
Fishing Opener Update: Soggy start, early showers, especially Wisconsin lakes. Mostly cloudy, windy and cooler, temperatures hold in the 40s northern Lakes (Leech) only reaching 50-53 for Gull, Pelican and the Whitefish Chainm possibly upper 50s for White Bear Lake and Minnetonka. Jackets will be required....clouds dominate with a few light showers/sprinkles, especially far northern Minnesota. It may look and feel more like mid October than early May. Sunday will be sunnier, milder, with less wind. A rising barometer both days may damped fish activity, but give it your best shot anyway!
Thursday: A drier, quieter day. Plenty of sun, still breeze, still mild. Winds: W 15-25. High: 74
Thursday night: Patchy clouds, still dry. Low: 47
Friday: Increasing clouds, good chance of PM showers. High: near 60
Saturday: Mostly cloudy, windy and cooler with a few showers, especially toward Leech Lake and the Grand Rapids-Duluth area. Most of the day will be dry - but chilly for May. High: 54
Sunday: More sun, less wind, a bit milder (and nicer to be out in a boat). High: near 60
Monday: Another round of showers moves in. High: 64
Tuesday: Breezy and milder, turning more humid. High: 69
Wednesday: Clouding up, showers and T-storms arrive. High: near 72