Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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361 FXUS63 KDLH 181912 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 212 PM CDT Wed Sep 18 2024 .KEY MESSAGES... - One round of showers and thunderstorms expected overnight tonight into Thursday. An isolated severe thunderstorm is possible over north-central Minnesota overnight. - Thursday afternoon into the evening, a second round of thunderstorms are expected to initiated along a cold front, with scattered severe storms possible. Large hail, damaging winds, a couple tornadoes, and locally heavy rain may occur. - Seasonable temperatures may return through the weekend and into next week. && .DISCUSSION... Issued at 211 PM CDT Wed Sep 18 2024 Another hot and muggy day has developed across the Northland with southerly flow bringing temperatures in the 80s and dewpoints in the 60s for much of the region. An approaching warm sector from a low pressure system coming out of the Northern Rockies is throwing an area of clouds and some showers over the Dakotas and western Minnesota early this afternoon. Those showers are expected to continue into north-central Minnesota later this afternoon and evening, with a boost by the LLJ overnight. This could lead to some elevated convection for the Brainerd Lakes to the International Border around midnight. With 1000-1500 J/kg of MLCAPE and around 30 knots of bulk shear, there may be an isolated severe storm of two in this convection, capable of briefly producing some large hail and damaging winds. As this area of showers and thunderstorms pushes northeast and outruns the best forcing as the LLJ is waning, precipitation coverage should decline through mid morning. As the stacked upper level low continues to progress along the International Border, a cold front should continue to march from west to east through the day, eventually leading to a secondary round of thunderstorms igniting in the afternoon. Morning precipitation could lead to some widespread mid to high clouds which should delay the time of ignition until late afternoon. Most CAMs have come into semi decent agreement for storm ignition in the 3-5pm timeframe along a north-south line. There is still some disagreement about the position of this line, but based on latest trends it`s likely to be past Brainerd-International Falls. These afternoon storms should be surface based, with a seasonably strong, moist airmass to support them. A narrow zone of 1500-3000 J/kg of MLCAPE, 30-40 knots of bulk shear perpendicular to the front, 6-8 C/km low level lapse rates, and well curved low level hodographs should support a discrete mode initiation with quick upscale growth and supercell potential. Large hail up to 2" in diameter may be one of the favored hazards early on, benefiting from late afternoon instability and that quick upscale growth. All hazards are on the table however, with a damaging wind threat increasing through the event as the line may begin to tend towards clustering. A tornado or two is possible as long as storms remain surface based, with models showing a potential plume of 100-125 m2/sec2 of 0-0.5km helicity. In addition to the severe threat, some quick downpours and locally heavy rain is possible, thanks to our very moist environment. However, no widespread heavy rainfall coverage is expected. Beyond Thursday, the Northland finds itself stuck between a high pressure over the southern Plains and an upper level trough bearing down from Canada. Embedded within that all could come some cut off lows and shortwave troughs. This should generally bring some cooler temperatures to the region, but our current above normal temperature situation may dally on it`s way out, with high temperatures not expected to reach their climatological normal of high 60s until Sunday. All the action in the upper levels may also keep chances for rainfall around. However, by and large global ensembles have backed off from a widespread washout precipitation solution, so there could be some sunshine scattered in there as well. && .AVIATION /12Z TAFS THROUGH 12Z THURSDAY/... Issued at 630 AM CDT Wed Sep 18 2024 A few isolated showers across MN this morning as the LLJ weakens. Through the day we are expecting VFR conditions with some gusts out of the south upwards of 20 kts. The latest models runs have been backing off the storm chances for this afternoon and making it more of an overnight feature. We will also have the LLJ to contend with once again bringing low level shear across the region once again overnight. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 211 PM CDT Wed Sep 18 2024 Southerly winds along the South Shore turn and become onshore for the Twin Ports and North Shore again today, with some gusts of 10-15 knots possible in the afternoon. Thursday, slightly stronger south to southeast winds are possible, sustained around 10-15 knots and some gusts near 20 knots in the Twin Ports and Chequamegon Bay. Rain showers and thunderstorms are likely Thursday, which may contain strong winds and large hail in the afternoon and evening. Friday, expected southwesterly winds with some breezy afternoon gusts behind Thursday`s cold front. For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. MARINE...None. && $$ DISCUSSION...Levens AVIATION...Britt MARINE...Levens