Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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660 FXUS63 KDLH 071745 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 1245 PM CDT Tue May 7 2024 .KEY MESSAGES... - A band of moderate rain moves into the Northland early this morning and spreads from southwest to northeast through this afternoon. Rain showers persist into tonight, especially in northeast Minnesota. - Scattered strong thunderstorms may (30% chance) form this afternoon mainly south of US Highway 2 and produce small hail and wind gusts to 40 mph. There remains a 5% chance of an isolated severe thunderstorm capable of producing around quarter size hail over inland northwest Wisconsin early this evening. - Fog late Tuesday night may be locally dense near Lake Superior. - Frost headlines for this warm season begin to be issued as of today. Frost is possible (40% chance) in the Arrowhead Wednesday night. Freezing conditions in northwest Wisconsin and widespread frost into the I-35 corridor and Arrowhead are possible (60% chance) Thursday night. - Two weak Canadian shortwave troughs passing over the area may (20-40% chance) bring additional light rain both Friday PM and Sunday. && .DISCUSSION... Issued at 348 AM CDT Tue May 7 2024 Vertically stacked low pressure centered over West River South Dakota is draping an occluded front over the Midwest early this morning. A band of rain and scattered thunderstorms persists along the occluded front in west-central Minnesota, but moving slowly north-northeastward. The first locally heavy rain showers have already formed in the Brainerd Lakes region over the last half-hour, with coverage expected to expand into east-central Minnesota and the western Iron Range. Precipitable water values of 1.1-1.2" shortly-incoming within this front-parallel flow pattern aid in very localized heavy rainfall and pea size hail being the expected primary hazards with this first round of rain showers. Short-term mesoanalysis shows increasing mid-level lapse rates in an area of 100-150 J/kg of MUCAPE supporting the 20% chance in the forecast for an isolated thunderstorm as well in this southwestern part of the Northland this morning. As the low pressure retrogrades westward into the Northern High Plains, better mid and low-level fgen forcing aids in a band of moderate rainfall forming from 5 AM to 8 AM, while lifting northeastward into the Iron Range, northwest Wisconsin and the Arrowhead as well. Anywhere from a few tenths to three-quarters of an inch of rainfall is expected this morning and into mid-day for areas along and south of the Iron Range in Minnesota and across all of northwest Wisconsin, except parts of northern Iron and Ashland Counties. After the main frontal band of rainfall exits the southern half of the Northland towards early afternoon, the better chances of scattered strong thunderstorms build into the region mainly along and south of US Hwy 2. An initial round of scattered strong thunderstorms is progged to again form in the Brainerd Lakes region between 1-3 PM today within an environment of minimal mid-level lapse rates (6 C/km) and CAPE (~100 J/kg). The minimal organized shear supports more of a pulse strong thunderstorm environment with collapsing updrafts fairly quickly to create downburst winds around 40-45 mph and maybe small hail around 1/2 inch in size. High-res, short-term models are in fair agreement on showing this storm environment quickly moving eastward into the east- central MN and inland northwest Wisconsin by early this evening. Slightly better mid-level lapse rates (6.5-7 C/km) and slightly more organized shear around 25 knots within a CAPE profile around 150 to maybe 200 J/kg is expected to help support the best potential (30% chance) for the strongest storms later today in inland northwest Wisconsin and maybe Pine County in MN from about 4-9 PM this evening. At this point, wind gusts to 45 mph and hail the size of nickels or smaller is expected in nearly all storms that may form. There is an outside (5-10% chance) potential of an isolated severe storm though just making it into southern parts of Washburn, Burnett, Sawyer and Price Counties later today. The primary threat would be large hail about an inch in diameter, but again only around 5-10% chance for any severe storm threat for this very limited coverage area. After the storm potential in inland parts of the Northland later this evening, rain showers and drizzle remain likely (60% chance) for the Arrowhead and Twin Ports through the overnight hours. Model forecast soundings show signals for overnight fog, most dense near Lake Superior, so areas of fog is mentioned in the forecast into early Wednesday morning. Easterly flow continues to create overcast skies for much of the region into Wednesday, but clearing in the Borderlands and near and south of US Hwy 8 is expected into the afternoon hours tomorrow while the isolated rain showers persist elsewhere. Due to vegetation becoming more susceptible to freezing temperatures and frost formation (per guidance from the Midwest Regional Climate Center) and the climatological trends for freezing temperatures ending from south to north this time of year in the Northland, NWS Duluth will begin the routine seasonal issuance of frost/freeze headlines again beginning today. With that said, the first potential for a frost headline may be Wednesday night in the Arrowhead as temperatures are forecast to get down to the 33-34 F (40% chance) at the surface to support frost formation. Although, even better and more widespread potential (60% chance) exists Thursday night for freezing temperatures in northwest Wisconsin and frost in the I-35 corridor and across the Arrowhead. Any headline potential will be further assessed on Wednesday, but this is an early heads up for those that have outside plants already or early starts to the garden! One item to watch for Wednesday night will be just how tight the remaining pressure gradient allows the near-surface winds to decrease to allow for optimal frost formation. An incoming shortwave trough from Canada Friday morning is expected to create at least some light rain showers, potentially localized moderate rainfall of another couple of tenths) that afternoon and evening. A similar setup on Sunday then looks to be another shot at widely scattered rain showers as well to end the weekend. Negating the easterly winds keeping stout lake breezes in play for within 50 miles of Lake Superior today through Thursday and temperatures in the 50s, inland locations will see high temperatures in the 60s for this forecast period. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1231 PM CDT Tue May 7 2024 A smattering of just about every flight category out there. While a wave lifts north, the same wave is expected to return tonight leaving a band of IFR or lower conditions over the forecast area. Thunderstorms are possible (60 percent chance) with afternoon convection, but will only extend as far north as 30 nm north of Duluth with the highest chances between 21Z and 03Z. Winds will be gusty to start with but will decrease tonight leading to potential fog formation. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 1231 PM CDT Tue May 7 2024 A constricted pressure gradient keeps elevated and gusty east to northeast winds late tonight, but further strengthening towards sunrise and mid-morning. The gustiest winds, near-gale force, are possible (40% chance) from Two Harbors to Grand Marais for a few hour period. Kept with only Small Craft Advisories for the short-duration and more stable regime keeping the strongest winds likely (60% chance) from reaching the surface waters today. Expect already elevated wave heights by early morning to further build into the mid-day period today and remain with elevated swell through tonight. There is a 20% chance of isolated thunderstorms from the Twin Ports to the South Shore this evening. Areas of marine fog are expected into early Wednesday morning (with a 30% chance of visibility less than 1 nautical mile). Gusty northeast winds persist, although slower in speed compared to today, on Wednesday with Small Crafts remaining in effect. 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...Gale Warning until 6 PM CDT this evening for LSZ140>144. Small Craft Advisory until 4 AM CDT Wednesday for LSZ145>147- 150. Small Craft Advisory until 4 PM CDT this afternoon for LSZ148. && $$ DISCUSSION...NLy AVIATION...Wolfe MARINE...NLy