Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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785 FXUS63 KDLH 182341 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 641 PM CDT Wed Sep 18 2024 .KEY MESSAGES... - Showers and thunderstorms expected tonight into Thursday. An isolated severe thunderstorm is possible over central and north- central Minnesota overnight. - Thursday afternoon into the evening, a second round of thunderstorms are expected to initiate 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. && .MESOSCALE UPDATE... Issued at 525 PM CDT Wed Sep 18 2024 A band of showers and a few embedded thunderstorms stretched from near Red Lake to near Grand Rapids to the Twin Cities as of 515 PM CDT and were moving north-northeast at 35 mph. This band of precipitation developed along the ascending branch of an 850 mb frontogenetic circulation on the northern periphery of a zone of stronger southerly 850 mb flow over western Minnesota and eastern North Dakota. Instability is quite limited in this area per the 22Z SPC RAP Mesoanalysis. MUCAPE is less than 1000 J/kg and MLCAPE is less than 500 J/kg. Nevertheless, the vigorous upward vertical motion supported some low-centroid storms over central Minnesota, embedded near the middle of the overall precipitation band. The 21Z RAP forecast has this feature continuing to lift north- northeastward across Koochiching, Itasca, and northern St. Louis county through early evening. There has been a recent weakening trend with the showers and particularly the storms. Think that trend will persist through 8 PM. Thereafter, there is still a potential for storms to redevelop later this evening and overnight as a southerly low-level jet strengthens and expands over western Minnesota and the eastern Dakotas. && .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 /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 641 PM CDT Wed Sep 18 2024 A band of rain showers with a few embedded thunderstorms from east of Winnipeg to Baudette, MN to near St. Paul, MN at 2330Z will continue to lift north-northeast through 03Z and will gradually weaken with time. Kept a mention of thunder at INL with this band of precip as that portion of the line is where the storms have persisted. A southerly low-level jet will strengthen over western Minnesota tonight and should support another round of showers and a few thunderstorms after 06Z. Those showers and storms should weaken through mid-morning. Another round of showers and storms is expected to develop ahead of a cold front which will move eastward across the Northland Thursday. Between bouts of precipitation, expect VFR conditions. && .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. && $$ MESOSCALE UPDATE...Huyck DISCUSSION...Levens AVIATION...Huyck MARINE...Levens