Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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770 FXUS63 KDLH 110846 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 346 AM CDT Tue Jun 11 2024 .KEY MESSAGES... - Rain showers and a few thunderstorms move eastward across the Northland this morning into early afternoon. A few isolated strong to near-severe storms are possible later in the afternoon into early evening over portions of northeastern Minnesota and NW WI. - Severe weather is expected on Wednesday, primarily during the late afternoon into evening. The main concerns will be very large hail (2"+ diameter) and damaging wind gusts. There is a lower-end threat for an isolated tornado that cannot be ruled out during the evening, but the potential is low (5% chance or less). - An active warm and wet weather pattern going forward, with additional shower and thunderstorm chances on Thursday, late Saturday into Sunday, and next week. && .DISCUSSION... Issued at 347 AM CDT Tue Jun 11 2024 Today: Moisture advection ahead of an approaching occluded front associated with a shortwave trough/surface low over southern Manitoba early this morning is bringing an area of light to moderate showers into central and north-central MN early this morning. This activity will continue moving eastwards across the Northland this morning though early afternoon, with a general window of 3-5 hours of rain for any one location as the showers move east. There could be a few embedded thunderstorms with this activity this morning into early afternoon, but no strong or severe weather is expected with this initial round of precipitation. Rainfall amounts of around 0.1-0.25" are expected with this initial round. There will be a brief break in precipitation behind this rain. Depending on how much clearing occurs behind the initial rain, a narrow pocket of 500-1100 J/kg of MUCAPE could develop by mid- afternoon amongst 0-6 km bulk shear values of 20-30 knots as the main forcing with the shortwave aloft moves overhead. Should this sufficient instability occur, isolated thunderstorms would develop along the occluded front in the mid-late afternoon in the vicinity of the I-35 corridor, with storms then moving east into the Arrowhead and NW WI into early this evening. The instability/shear combination would support a couple of these storms becoming strong to marginally severe before storms diminish past the early evening. The main hazards would be hail up to 1 inch in diameter and wind gusts up to 50-60 mph, with the best severe potential (5% chance) in Burnett, Washburn, and Sawyer counties in NW WI where instability looks to be highest. Wednesday: A few showers and non-severe storms could occur again later tonight into Wednesday morning in the wake of this low pressure system, but little in the way of additional rainfall is expected. Otherwise, the focus turns towards the more likely severe thunderstorm potential for later Wednesday afternoon into evening. Strong moisture advection from the Gulf of Mexico will be ongoing throughout the day, pushing dewpoints into the 60s by the afternoon along with high temperatures soaring into the 80s. This will make it feel like the muggiest day the Northland has seen so far this Spring. An approaching shortwave trough and surface low/cold front from the Canadian Prairies will eventually kick off shower and thunderstorm development later Wednesday afternoon. These storms will have access to a very buoyant warm sector with this system ahead of the front, denoted by MUCAPE values of 1500-3000 J/kg and locally higher amounts due to steep low and mid-level lapse rates. 0-6 km and 0-10 km bulk shear vectors of 45-55 knots and 75-90 knots, respectively, will be generally parallel with one another, favoring initial thunderstorm development as discrete supercells. The high amount of instability, shear, and supercellular storm mode will favor the primary threat during the afternoon being very large hail to 2"+ in diameter. The potential for supercells will be mainly in north-central and northeast Minnesota during the afternoon, but the best potential for the very large hail will be where instability is expected to be highest, which is an area generally bounded on the north by the Brainerd Lakes to Duluth to Siren. These supercells will also pose a threat for damaging wind gusts as well. While there will be some SRH values in excess of 100 m2/s2, LCLs during the afternoon will initially be a bit too high to favor much tornado development. Hodographs do show a little bit better low-level turning along with lowering LCLs heading into the early evening, so a low end threat (5% chance or less) for a tornado or two cannot be ruled out heading into the evening. Heading towards sunset and later into the evening, storms are expected to grow upscale into more of a line of storms, leading to the threat becoming primarily wind at that point. However, the farther we progress into the evening, instability will be on the downward trend with storm intensities gradually weakening and eventually moving southeast out of the area prior to Wednesday night. Updates to the favored locations of storm development are still likely as highlighted by the various placement of storms in short-term model guidance with the 06Z model suite. Thursday: A stationary front and subtle shortwave trough may lead to additional shower and thunderstorm chances on Thursday in the wake of the Wednesday system. Despite strong shear vectors continuing, this will be a much less moist airmass, with very meager instability to tap into as a result. Therefore, severe weather is not expected on Thursday. Friday: Surface high pressure and shortwave ridging aloft bring a brief break from the rainy pattern for Friday into early Saturday. Expect sunnier skies, light winds, and high temperatures in the mid-70s to around 80 degrees on Friday. This Weekend: The active weather pattern rears its head again later on Saturday into Sunday as the ridge shifts off to our east and global model guidance hints at a southern stream shortwave trough moving across the Upper Midwest in phase with a more robust shortwave/closed low moving northeastward across southern Saskatchewan into northern Manitoba. This pattern should set up southwesterly flow once again across the Northland, advecting a much more moist airmass into the region once again. Still a bit to early to get into the details, but the synoptic parameter space (sufficient instability and bulk shear vectors around 30 knots) could support a severe weather threat, particularly on Sunday given the longer duration of moisture and temperature advection. Sunday could even see widespread high temperatures in the 80s once again. Given still wet soils and near to above- normal streamflows, PWATs potentially approaching 2 inches, and model soundings showing deep saturation with temperatures above freezing to above 10 kft, this system could also pose a low- end threat for heavy rainfall and minor flooding across much of the Northland as highlighted by the Day 5 Marginal WPC Excessive Rainfall Outlook. Early Next Week: Global ensemble guidance diverges into next week, with the timing of additional shortwaves/low pressure systems becoming increasingly uncertain. However, the generally southwest to quasi-zonal flow pattern aloft would favor periodic impulses, and additional shower/thunderstorm chances as a result, into next week. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1244 AM CDT Tue Jun 11 2024 VFR conditions to start. Rain moving in from the west later during the current overnight hours through Tuesday morning will bring high confidence in IFR or lower ceilings with it, and some MVFR to perhaps at times IFR visibilities. There is a 10% chance for some thunder in the vicinity of KBRD between 09-12Z, but potential is too low to include in the TAF at this time, though amendments may be needed. Also expect some wind shear early this morning for KINL an KBRD before winds pick up during the day. There will be a brief break in precipitation behind the morning showers before a narrow window of time/area for isolated thunderstorms develops along an occluded front mid-afternoon along the I-35 corridor and pushes east into the Arrowhead and NW WI into early evening. Given the more isolated nature of the storms, kept thunderstorm mention primarily in PROB30 or VCTS groups. Conditions quickly improve to VFR later this afternoon and evening as skies clear behind the front. Light southeast winds during the current overnight will veer to westerly behind an occluded front later this morning through afternoon from west to east. Daytime winds around 10-12 knots will gust up to around 20 knots through the afternoon before turning light into this evening and tonight. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 347 AM CDT Tue Jun 11 2024 Winds will be southerly along the South Shore and northeasterly along the North Shore today, with gusts remaining less than 20 knots. A few isolated storms are possible this afternoon into early evening, though no strong to severe storms are expected when they move over the Lake. Winds turn light out of the southwest this evening and tonight. As another low pressure system and cold front approach from the west on Wednesday, winds will increase out of the southwest with gusts up to 20 kts. Hazardous small craft conditions are not currently expected given the warmer air temperatures over land and more stable marine layer over the Lake, but will need to be monitored. Another round of storms Wednesday evening may be strong to severe over western Lake Superior. Winds turn breezy out of the west on Thursday behind a departing cold front, which will lead to a 50-60% chance for Small Craft Advisory level wind gusts of 20-25 knots during the late morning and afternoon. 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. && $$ DISCUSSION...Rothstein AVIATION...Rothstein MARINE...Rothstein