Threat for a few strong to severe thunderstorms Thursday; turning warmer and more humid this weekend into early next week (record warmth possible Sunday-Monday)

Isolated strong to severe thunderstorms are possible over much of the Northland Thursday and Thursday night.

The setup for Thursday features a warm front well northeast of our area, while a cold front moves east out of western Minnesota. Southerly winds ahead of that cold front will advect warm and humid air northeast into our area thanks to a strong low level jet of 40-60 knots. Dew points are forecast to climb into the low 60s on Thursday while CAPE increases to around 1000-1500 J/kg. Winds aloft and wind shear will be on the strong side, with 500mb winds of 50 to nearly 70 knots across the area, while 0-6 KM wind shear ranges from 40-60 knots, with around 30-40 knots of Effective Bulk Shear, all of those ingredients are favorable for severe weather. Will also have steep mid level lapse rates >7.0 c/km, and a change of wind direction with height, those two ingredients may lead to an increase risk for a few supercell thunderstorms with a threat for large hail, otherwise we’re looking at a damaging wind threat with any severe thunderstorms that develop on Thursday.

Note: Timing and capping issues are present with Thursday’s setup as 700mb temps range from around +7 to +10C, this could make it difficult for storms to either develop or sustain themselves if storms do develop, while a later timing of the cold front could mean most storms hold off until after sunset Thursday.

So there’s still some uncertainty regarding the severe threat for Thursday, but the overall setup is favorable for some severe weather in parts of the upper Midwest and in the Northland. Stay tuned.

Currently there is a Marginal Risk (dark green area on map) for severe thunderstorms which covers a large portion of northeast Minnesota and most of northwest Wisconsin for Thursday, and we could see this risk upgraded to a Slight Risk in future updates. Stay tuned.

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A warm front moving ENE across the area Wednesday evening into Thursday morning could cause some showers and isolated thunderstorms in the Northland but severe weather is not expected with this activity.

18z NAM 3km model simulated radar forecast valid from 7 PM Wednesday to 1 PM Thursday.

Updated precipitation deficits in the Northland after Monday night’s rain event.

Duluth, MN

Month to date: -0.01″ below normal
Year to date: -5.82″ below normal

International Falls, MN

Month to date: -0.79″ below normal
Year to date: -7.40″ below normal

Hibbing, MN

Month to date: -0.41″ below normal

Ashland, WI

Month to date: -0.34″ below normal

Brainerd, MN

Month to date: -0.26″ below normal

…More rain on the way…

Rainfall totals of a quarter to over a half an inch are possible in northeast Minnesota and northwest Wisconsin Wednesday night through early Friday morning.

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The pattern from this weekend into early next week still looks like a warm one for northeast Minnesota and northwest Wisconsin as an upper level ridge strengthens across the Great Lakes while a trough digs S/E across the western U.S. This setup puts our area in a warm SW flow aloft, with the Sunday and Monday time frame looking like the warmest days at the moment, that’s when we could see widespread 80+ degree highs in the Northland. A more humid air mass will also occur along with the warm temps as dew points climb into the 60s by Sunday and Monday.

Note: We could see record or near record warmth for both high and low temperatures in the Northland September 19-20.

12z Euro Ensemble model 500mb Anomaly Forecast valid September 18-22, 2021.

Looking ahead into the middle to end of next week includes the potential to see our first widespread frost/freeze of the season in the Northland.

Temperature Anomaly Forecast valid September 22-25, 2021.

Green and blue colors=Below normal temperatures

Date of first freeze (32 F) in the Northland using the new 1991-2020 climatological period.

Much of the Northland, except for Hibbing is still waiting for their first 32 F freeze of the season, but normally we don’t see that first freeze occur until mid or late September, so we’re inching closer to that time frame.

Hibbing, MN: September 10. First 32 degree freeze this year was on September 6.

International Falls, MN: September 15. Last year’s first freeze (32 F) was on September 8.

Ashland, WI: September 24. Last year’s first freeze (32 F) was on September September 9.

Brainerd, MN: September 25. Last year’s first freeze (32 F) was on September 9.

Duluth, MN: September 30. Last year’s first freeze (32 F) was on September 17.

Tim

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