613 FXUS63 KDLH 090549 AFDDLHArea Forecast Discussion National Weather Service Duluth MN 1249 AM CDT Tue Sep 9 2025
.KEY MESSAGES...
- Showers and thunderstorms expected tonight into Tuesday. An isolated strong to severe storm will be possible mainly in the Brainerd Lakes area with large hail the primary threat.
- Rainfall may be heavy at times and may lead to localized flash flooding.
- A dry and warming pattern takes over for the remainder of the week with rain chances returning heading into the weekend.
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.DISCUSSION... Issued at 331 PM CDT Mon Sep 8 2025
High pressure was in control across the eastern Great Lakes this afternoon and extended to the southwest into the Southern Plains. An elongated area of low pressure was in place over the Northern Plains with a warm front extending from southern North Dakota into central Minnesota and far western Wisconsin. A cluster of elevated thunderstorms was observed on radar across portions of Koochiching, Itasca and St. Louis counties. This cluster was located at the head of an MUCAPE gradient stretching from the Dakotas into western and north-central Minnesota. SPC mesoanalysis shows up to around 500 J/kg of MUCAPE where the storms are with around 30 knots of effective shear. Storms haven`t shown much organization thus far but slightly better shear does arrive as the evening progresses as a low-level jet spread across the region behind the advancing warm front.
Forecast soundings continue to show a capping inversion persisting into tonight, which should limit any surface based storms and keep them elevated. This will lead to a marginal large hail threat with marginal mid-level lapse rates and, while CAPE profiles are overall skinny leading to more of a heavy rain threat, the thickest part of the profiles is through the HGZ. Should a storm become surface based, there is a non-zero tornado threat with fairly strong speed and directional shear in the 0-1km layer and SRH over 200 m2/s2. Multiple rounds of showers and storms are expected for tonight into Tuesday as the warm front stalls out over the region and then starts to slowly move southeast as a cold front Tuesday. The best chance for any strong storms this evening will be in the Brainerd Lakes area and south/west of a Cass Lake to Grand Rapids to Hibbing to Cloquet to Hinckley line. Given the potential for multiple rounds of storms and continued moisture feeding into the region, some isolated flash flooding will be possible. The heaviest rainfall amounts look to stretch from the Iron Range into the Arrowhead where 1 to 2 inches plus of rainfall will be possible. The area of heavier rainfall potential then shifts into northwest Wisconsin for Tuesday.
High pressure will build in for mid-week with upper level ridging pushing in from the west as well. This will lead to dry conditions with temperatures warming into the 70s with even some low 80s by Friday. Rainfall chances then return for Friday into the weekend with a cutoff low dropping southeast from St. James Bay into southwestern Ontario along with a baroclinic zone setting up from the northern High Plains into the Great Lakes for the weekend into early next week. Temperatures will then cool back into the 60s and lower 70s to start the new work week.
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.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1249 AM CDT Tue Sep 9 2025
Most weather models continue to poorly handle the ongoing convection, so have backed off on prevailing thunderstorm mention at most terminals overnight and relied heavier on VCTS and PROB30 groups. With that said, HIB/DLH have the best potential to see ongoing shower/storm potential overnight given proximity to a stationary front. Look for generally MVFR to VFR visibilities for them in showers, with occasional dips to IFR visibility for any storms that move overhead. Showers and storms are generally slow moving, but the front should start slowly sagging south today, pushing farther southeast into northwest Wisconsin for much of today. Outside of storms, expect current VFR to MVFR ceilings to plummet to IFR to LIFR towards early morning for northeast Minnesota terminals towards early morning, lingering towards midday. This area of IFR ceilings should shift into northwest Wisconsin later in the morning into afternoon/evening as the front and precipitation slides southeast, with conditions gradually returning to MVFR/VFR for most northeast Minnesota terminals mid to late today. LIFR to VLIFR conditions in dense fog persist at INL into early this morning, before gradually improving towards mid to late morning. LLWS persists towards 08Z for DLH and 10Z for HYR prior to the low- level jet weakening.
Look for more widespread fog to dense fog and low stratus potential towards or just after the very end of the current TAF period Tuesday night given light winds and lingering low-level moisture.
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.MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 331 PM CDT Mon Sep 8 2025
Rounds of showers and thunderstorms will be seen this afternoon into Tuesday with activity becoming more focused along the South Shore as the day progresses Tuesday. Lightning and small hail will be the primary threats with any storms. Winds will be southerly to southwesterly with gusts to 20 to 25 knots tonight into Tuesday from the Outer Apostles to Saxon Harbor. Small Craft Advisories have been issued through late Tuesday morning for this threat. Winds remain southwesterly for Tuesday and decrease to 10 to 20 knots during the afternoon before further weakening Tuesday night and becoming northeasterly at 5 to 15 knots for Wednesday.
For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt.
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.DLH WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. MARINE...Small Craft Advisory until 10 AM CDT this morning for LSZ121- 148-150.
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DISCUSSION...BJH AVIATION...Rothstein MARINE...BJH
NWS DLH Office Area Forecast Discussion