THE NATIONAL WEATHER SERVICE IN LA CROSSE HAS ISSUED A
* SEVERE THUNDERSTORM WARNING FOR...
EASTERN WABASHA COUNTY IN SOUTHEAST MINNESOTA...
BUFFALO COUNTY IN WEST CENTRAL WISCONSIN...
* UNTIL 545 PM CDT
* AT 505 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL...AND
DAMAGING WINDS IN EXCESS OF 60 MPH. THIS STORM WAS LOCATED NEAR
KELLOGG...OR NEAR ALMA...MOVING EAST AT 50 MPH.
(update, 4:38 pm) Doppler radar shows strong storms rumbling across southeastern MN. Those little green triangles represent hail (generally 1/2" in diameter). Keep in mind that the criteria for what is a "severe thunderstorm" has changed. Last year it was 3/4" diameter - now it's been changed to 1" diameter hail, roughly quarter-size, large enough to cause damage to rooftops, windows and car surfaces. St. Cloud and the Twin Cities are on the dry, quiet side of the front - but these storms will probably continue to intensify as they rumble into southeastern MN and western Wisconsin. I do expect some warnings to be issued between 5 and 7 pm. The next chance of thunder for our area will come Friday, but moisture may be too limited for anything severe. There's a better chance of a severe storm outbreak by next Tuesday-Wednesday as temperatures climb toward 80 and dew point temperatures top 60. If the wind profile is ripe (lot's of "shear", winds changing in speed and direction with altitude) then conditions may be present for severe weather. Too early to tell, but next Tuesday looks like the first real potential for watches/warnings in the immediate area.
(update, 2:25 pm) Latest Doppler radar analysis (using GR3 software) shows hail-producing T-storms mushrooming over southeastern MN and west central WI. Estimated hail size of 3/4" near Kenyon and 1/2" over Cannon Falls, and these storms will in all probability continue to strengthen over the next few hours, peaking between 5 and 6 pm, after the high temperature for the day, when the atmosphere is most unstable. I do expect some severe storm warnings to be issued for far southeastern MN and much of Wisconsin - damaging hail, straight-line winds, even an isolated tornado can't be ruled out in this kind of a pattern. Low-level moisture and wind shear is sufficient for a few severe storms, although the major tornado outbreak is expected a couple hundred miles south/east of MSP, deeper into the moist, unstable air, from eastern Iowa and Missouri to northern Illinois and southern Wisconsin. We are on the fringe of the severe weather threat, but I still expect any strong to severe storms to flare up south/east of St. Paul and Minneapolis. Stay tuned...
NOTE: This is a special Doppler field called "VIL Density" which measures the potential for significant hail within a thunderstorm. The bright pink areas are regions where hail may be largest, in excess of 1/2 to 3/4" in diameter. All these storms are moving steadily east.
(update 1:45 pm). Doppler radar shows persistent bands of rain pushing across east central and southeastern Minnesota. This line of moderate/heavy rain should intensify as it moves east, possibly becoming severe over extreme southeastern MN and much of Wisconsin. Watches and warnings may have to be issued later today, probably well south/east of the Twin Cities. That said, damaging hail, straight-line winds, even an isolated tornado, can't be ruled out from Rochester and Winona to Menomonie and Eau Claire, WI later today. Meanwhile wind advisories are posted for roughly the western half of Minnesota for west winds gusting to 40 mph or higher. Rain should shift east with gradual clearing for the Twin Cities metro area later this afternoon and evening - you may still be able to squeeze in your outdoor activities, especially after 4 or 5 pm. We'll keep an eye on Doppler and keep you posted right here.
The 1 km. visible satellite image shows sunshine across much of Minnesota, the only exception from the Twin Cities on south/east, where showers and T-storms are developing and strengthening throughout the afternoon and evening hours. St. Cloud, Willmar and Garrison are in the clear, and the heavy-weather risk should pass the immediate Twin Cities metro area by 3 or 4 pm.
You've heard the expression before: "bolt from the blue" or "out of the blue". I'm referring to a weather phenomenon that claims more lives in the USA than tornadoes and hurricane combined...lightning. Every year nearly a dozen people are killed by lightning, struck dead with blue sky directly overhead, a thunderstorm 5-10 miles away. Lightning can travel horizontally up to 10 miles away from the parent thunderhead. The solution? Wait at least 30 minutes after hearing the last thunderclap before heading back outside, to be absolutely safe. Remind your kids about the 30-30 Rule. If you can count 30 seconds between seeing the "flash" of lightning and hearing the "bang" of thunder, you're in danger - time to head indoors. And at the tail end of a storm wait at least 30 minutes after the last thunder before venturing back outside. Just because the rain has subsided does NOT mean the lightning risk has passed. The Twin Cities area experiences an average of 35 "lightning days" every year.
Here are more tips that a thunderstorm may be especially severe:
* Lightning can be detected on your AM radio. These electromagnetic bursts show up as static on your AM radio dial. If you hear nearly continuous static it's a tip-off that a line of thunderstorms may be approaching.
* Thunderstorms are most likely around the dinner hour, when the atmosphere is most unstable.
* Before a storm strikes winds at the ground usually blow from the south or southeast. T-storms are rare when surface winds are blowing from the west, northwest or north.
* Look for cues in nature: the old proverb "birds fly low before a storm" has some scientific merit: apparently birds fly near the ground to relieve air pressure in their ears; the barometer usually falls sharply ahead of a T-storm.
* An eerie, greenish color to the sky and large hail are tip-offs that a storm may be especially severe, even capable of spinning up a tornado.
According to SPC, the Storm Prediction Center in Norman, Oklahoma, there is a slight risk of severe storms over southeastern Minnesota and all of Wisconsin Wednesday, a moderate risk from near St. Louis to Chicago (where a significant tornado outbreak is expected later in the day).
SPC now predicts the probability of severe weather within 15 miles of any point. For example, Wednesday there is a 15% chance of 58 mph+ winds and/or 1"+ hail over southeastern Minnesota, but that rises to a 45% risk from Missouri to Illinois. If you want to know the risk of severe storms you can check out the details for yourself by clicking on the SPC Outlook, which is updated 24 hours/day. There is a wealth of severe storm information here.
* Best chance of rain/T-storms: first thing today (wet roads may slow down the AM commute in some towns).
* Winds shift to the west later today, gusting past 30 mph. at times.
* Basically dry from midday Wednesday into Thursday.
* Thursday: nicest day in sight with bright sun and less wind.
* Computer models print out another .20" of rain Friday.
* Weekend outlook: Saturday looks like the sunnier, nicer day. Showers/T-storms may spread across northern Minnesota Sunday PM, possibly reaching the St. Cloud area by mid afternoon.
Wednesday: Morning shower, stray T-storm, then increasingly sunny, windy and mild. Winds: SW/W 15-30. High: near 70
Wednesday night: Mostly clear and chilly. Low: 45
Thursday: Mostly sunny and beautiful with less wind. High: 65
Friday: Showers move back in, possible thunder. High: 63
Saturday: Better day of the weekend for outdoor activities. Plenty of sun. High: 62
Sunday: Sunny start, clouds increase. Risk of PM T-storms, especially northern MN. High: 67
Monday: Partly cloudy, breezy and mild. High: 72
Tuesday: Warm with PM T-storms, some potentially strong. High: 76