Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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796 FXUS63 KDLH 250603 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 103 AM CDT Tue Jun 25 2024 .KEY MESSAGES... - Still a conditional severe thunderstorm threat for this evening into early tonight for the Northland. Hazards include large hail, damaging winds, and a lower (2% chance) tornado potential. - Scattered showers for some on Tuesday and mostly dry Wednesday. - Additional showers and storms Thursday into Saturday and again early next week. && .DISCUSSION... Issued at 435 PM CDT Mon Jun 24 2024 Rest of Today - Tonight: While the forecast has honed in on the areas of concern for severe weather potential this evening into early tonight, there still remains some uncertainty with regards to if and when severe storms develop this evening. All of the Northland remains in a Slight Risk for severe weather (Level 2/5) with some slivers of a "higher end" severe threat. As of 430 PM CDT this afternoon, elevated scattered showers and a few embedded rumbles of thunder were present in the Brainerd Lakes vicinity in an area of very subtle 500-mb troughing perturbations. This activity will continue to move east through the remainder of the afternoon. Much of the Northland remains strongly capped for surface-based air parcels with current RAP forecast soundings showing 150-300 J/kg, though capping is a bit weaker farther northwest near a surface cold front over SE Manitoba/SW Ontario/NW MN. This region is where initial development of thunderstorms late this afternoon is most likely where forcing is better, as is hinted at by several short-term models, including most of the WoFS ensemble members. Thunderstorms in this region are forecast to see MLCAPE values of 2000-3000 J/kg where effective shear is 45-55 kt out of the west. This would be a roughly 45-degree angle relative to the cold front, so initial convective development would favor a discrete supercellular storm mode. Given the favored storm mode and mid-level lapse rates around 7-7.5 C/km, the primary threats would be large hail (1+") and wind gust up to 60 mph as these storms move east into north-central Minnesota by 6-8 PM timeframe, and then moving farther east with time into the Arrowhead the remainder of the evening into early tonight. Also can`t rule out a low-end tornado potential (2%) through mid- evening given 0-1 SRH values of 150-200 m2/s2. The loss of daytime heating will lead to increasing MLCIN mid to late evening over north-central MN, so expectations are for severe potential to diminish as storms move farther into the Arrowhead towards 10pm-2am timeframe. The second--and more conditional--area of severe thunderstorm concern this evening into early tonight is from central MN into NW WI as this area has been plague by more persistent cloud cover, lingering showers, and a stronger capping inversion for much of the day. This area would be closer to the surface warm front moving northward from its position in SW/south-central MN. If storms can break the cap, it wouldn`t be likely till a little later into the early evening hours (looking more towards 8-9 PM in the Brainerd Lakes/east-central MN as another subtle 500-mb shortwave moves through. Storms in this area would have access to MLCAPE of 2500-4000 J/kg with very steep mid-level lapse rates, around 50 kt of westerly effective shear, and 0-1 and 0-3 SRH of 150+ and 250+ m2/s2, respectively. These storms would favor a quicker upscale growth into a cluster of storms or a bowing line segment given shear being oriented more parallel to the surface front. The main concern with these storms would be damaging wind gusts to 60 mph, as well as large hail to 1 inch in diameter initially. The low-level turning/SRH would support a low tornado threat (2%) for the surface based storms that don`t become outflow dominant. Short term guidance still disagrees on where/if these storms develop given the strong cap. There is also a real potential that these storms may develop just to the south of our forecast area and remain that way due to the gradient of higher instability being just south of central/east-central MN and track east/southeast while remaining completely out of our area. If storms develop in central/east- central MN, then these storms could continue to track east into NW WI, as well. Instability will be less with eastward extent, so expectation is for storm intensity to weaken with eastward extent into the later evening and early overnight hours before storms exit eastern parts of the CWA. Widespread heavy rain is not expected due to the faster storm motions and more progressive nature of storms this evening and tonight. However, PWATs of 1.7-2" will support efficient rainfall rates, so some localized pockets of 1-2" could be observed mainly in east-central MN to NW WI. Tuesday - Wednesday: Some showers are expected across far Northern MN late Tuesday and Tuesday night in cyclonic flow aloft. May see an off chance for a stray shower on Wednesday, but chances are 10% or less. Temperatures in the mid-70s to mid-80s are expected for Tuesday, but be cooler in the 70s on Wednesday. Thursday - This Weekend: A series of shortwave troughs move through the Upper-Midwest on Thursday-Saturday, with a surface low pressure moving across the region on Friday into Friday night. This will bring additional shower and thunderstorm potential, though severe weather is not anticipated at this time. We will have to watch for some limited heavy rain/flooding potential given elevated streamflows and wet soils, however. Exact amounts and locations are still uncertain and too low-confidence to pin down at the moment. There should be a brief break in rain again on Sunday as ridging/surface high pressure move through. Early Next Week: Another active pattern with more shower/thunderstorm chances as more shortwave energy/surface low moves somewhere through the north-central CONUS/far south-central Canada. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 103 AM CDT Tue Jun 25 2024 Showers and thunderstorms will clear northwest Wisconsin over the next few hours. Mainly clear skies are expected to follow over the next few hours as a cold front works through the region. VFR conditions will then persist through the remainder of the period. Biggest concern for the period will be northwesterly winds gusting to 20-25 knots for much of the day before diminishing around sunset. Some clouds return late in the period with some showers possible at INL by the late evening hours, but confidence too low to include at this time. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 435 PM CDT Mon Jun 24 2024 Lighter onshore winds with speeds less than 15 knots continue for the remainder of today. There is a chance for thunderstorms this evening into early tonight, with a large hail threat and winds in excess of 45 knots, with the best chance along the South Shore. Winds will switch to westerly behind a cold front tonight and increase late to 10 to 15 knots with gusts around 20 knots. Winds increase further on Tuesday from the west, with gusts up to 25 knots and hazardous conditions for small craft for late Tuesday morning through mid-evening, where a Small Craft Advisory is in effect. Winds will veer to northeast Tuesday night into Wednesday and diminish to less than 15 knots. 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...Small Craft Advisory from 11 AM this morning to 9 PM CDT this evening for LSZ121-140>148-150. && $$ DISCUSSION...Rothstein AVIATION...BJH MARINE...Rothstein