Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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270 FXUS63 KDLH 171801 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 101 PM CDT Fri May 17 2024 .UPDATE... Issued at 634 AM CDT Fri May 17 2024 Mid-level clouds associated with an area of scattered rain showers has moved over central and northern St Louis County over the last two hours, helping to reduce the coverage of dense fog. Webcam imagery and surface observations over the last hour have shown continued improvement and any lingering pockets are very likely to lift over the next hour so the Dense Fog Advisory was cancelled early just now. && .KEY MESSAGES... - Scattered rain showers and isolated thunderstorms occur today, mainly in the morning and early afternoon. A few thunderstorms may (20% chance) occur later this afternoon and early evening though. - Temperatures warm into the mid 70s to low 80s today and Saturday. - Scattered strong thunderstorms, a few marginally severe in the eastern Arrowhead and north-central Wisconsin, remain possible (40% chance) in the Arrowhead and across northwest Wisconsin Saturday afternoon to mid-evening. && .DISCUSSION... Issued at 350 AM CDT Fri May 17 2024 Dense fog continues to be observed on surface observation stations and shown on infrared satellite imagery in central and northern St Louis County early this morning. An incoming mid- level stratus shield may improve visibilities ahead of scattered high-based rain showers, but keeping the ongoing Advisory in place for now and will adjust end timing as observations, webcams and/or satellite imagery indicated longer term visibility improvements later this morning (currently expected around 6-7 AM improving visibility though). A warm front passes over the region early this morning, helping to create the current scattered high-based rain showers in north-central Minnesota that move into northeast Minnesota closer to the dawn and sunrise hours today. Warm southerly flow ushers in a much warmer air mass today as a result behind this area of showers. Temperatures warm into the low-80s for the Brainerd Lakes, east-central MN and into northwest Wisconsin today. The South Shore lake shore communities keep fairly cooler though as easterly flow off the Big Lake advects onshore. Most precip chances taper from southwest to northeast this afternoon and evening, but kept broad slight to chance PoPs in the forecast for high-res model guidance indicating a sparse coverage of later afternoon and early evening thunderstorms in northwest Wisconsin, closer to the Ports and across the Iron Range/Arrowhead. The main message is keep aware of isolated rain shower and thunderstorm development even in this afternoon to early evening time period today. The warmest air pushes out of the Brainerd Lakes region tonight and into north-central Wisconsin by Saturday creating residual low-80 high temperatures tomorrow for east-central MN and across northwest Wisconsin. The downsloping regions in far northern Ashland County off the Penokees could even see mid-80s out of this flow pattern tomorrow afternoon. The incoming cold front associated with the warm front draping down from low pressure centered in Manitoba later today and throughout tomorrow creates the best chances for strong thunderstorms in the Arrowhead and northwest Wisconsin Saturday afternoon and early evening. A narrow wedge of just-enough instability (800-1000 J/kg of CAPE) supported by decent mid- level lapse rates around 8-8.25 C/km are present in mainly northwest Wisconsin, but just pushing into the far eastern Arrowhead by late afternoon Saturday. Available moisture within the thermal profiles shown on high-res guidance supports dime and nickel size hail, potentially around a quarter in size (a.k.a low-end, marginal severe), with gusts around 50 mph closer to an area from Bayfield to Sawyer Counties and eastward into north-central Wisconsin; the eastern half of Cook County is much less likely to see anything but sub-severe storms. As was discussed previously, the shear will be the limiting factor for the marginal severe potential over a few hour period in northwest, but mainly north-central, Wisconsin tomorrow afternoon. Dry air quickly builds in behind the passing cold front Saturday mid-evening and early night leading to dry and still-warm conditions for Sunday. A shortwave trough moving out of the Central Rockies on Sunday phases with a deeper Southern Canadian Plains mid-level trough to create the next round of storms and rain showers in the Northland early next week. Depending on the placement of the best forcing (somewhere in Wisconsin or eastern Minnesota) a half-inch of rainfall is entirely possible (40-60% chance) for east-central Minnesota and/or northwest Wisconsin Monday daytime into Monday night. Right now, the best ingredients for severe weather appear just south of the region, but something to watch out for though if a northerly shift occurs over the next couple of days. Another mid-week system could bring another round of rain showers to the region for later Tuesday into Wednesday. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 100 PM CDT Fri May 17 2024 It`s looking like we should see a nice break from any showers/storms for the rest of the afternoon and early evening, aside from a shower or two passing through HYR within the next hour. While the air following behind this initial area of clouds and showers is warm, it is also dry, and thus there isn`t much to support additional showers/storms this afternoon. There may be a 10-15% chance that a stray shower/storm could develop, but not enough confidence to put in any TAFs. Later this evening, warm air advection continues out ahead of an approaching cold front from the west. We will likely see some scattered showers/storms developing and passing by overnight. In addition, periods of fog may be possible away from any showers/storms, so expect occasional MVFR to potentially briefly IFR ceilings and visibility tonight. LLWS is also expected overnight with a potent low-level jet developing. The shower/storm chances will continue through about mid-day at Minnesota terminals, ending after the cold front passes through. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 315 AM CDT Fri May 17 2024 Dense fog remains early this morning per satellite and webcam imagery so the Dense Fog Advisory remains in effect until 10 AM today. Calm winds this morning become easterly at 10-20 knots this afternoon and evening, creating wave heights to 4 feet near the head of the lake. Held off on any Small Craft Advisory for now, but a near-term issuance may be needed for Two Harbors to the Twin Ports to Port Wing if those gusts do approach 22-25 knots this afternoon. Another night of dense fog may occur as well tonight. Southwest winds increase Saturday, with gusts to 25 knots mostly expected at the head of the lake. 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. && $$ UPDATE...NLy DISCUSSION...NLy AVIATION...JDS MARINE...NLy