Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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866 FXUS63 KDLH 240835 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 335 AM CDT Mon Jun 24 2024 .KEY MESSAGES... - A highly conditional threat for severe thunderstorms exists for this afternoon into tonight across the Northland. Hazards include large hail, damaging winds, and a tornado but is dependent on timing and storm mode which is still questionable. - Dry weather expected for most Tuesday and Wednesday. - Periodic chances for more showers/storms Thursday into next week. && .DISCUSSION... Issued at 238 AM CDT Mon Jun 24 2024 The forecast focus will be on this afternoon into tonight and the chance for severe thunderstorms, with the possibility of a more high end severe threat. Most of the Northland remains under a Slight Risk (2/5) but this is a "higher" end Slight Risk. A warm front across the Northern Plains early this morning will move north today and should be just off to the west and south of the Brainerd Lakes by this evening. A low amplitude upper ridge will be over the area but will move east and weak height falls will move over the region this afternoon. Southerly winds will draw moist air north (PWAT values rising to 1.7-2.0") along with very warm temperatures. Highs this afternoon will reach the lower to middle eighties over much of the southern half of the area. An elevated mixed layer moving in will contribute to mid-level lapse rates of 7.5-8.5c/km. Very high to extreme MLCAPE values (2000-4000j/kg) will develop over or very close to the Northland with a north to south gradient. 500MB westerly winds around 50 knots will contribute to effective shear of 40kts+. Forecast soundings show plenty of curvature from 0-3km and 0-1km SRH will be from 150+ m2/s2, with the RAP forecasting values up to 300 m2/s2 over southern areas. Most of the ingredients are present for a significant severe weather event across the Northland. However, one significant impediment will be the presence of a stout cap, especially over the southern half of the Northland. 750-800mb temperatures are forecast to be around 20C and RAP soundings reveal very high MLCIN values (200-300+ J/kg). The cap is weaker in far northern Minnesota though. Will the cap be overcome by a subtle shortwave aloft, frontal convergence, and persistent warm air/moisture advection from a low level jet (that will strengthen this evening)? That is the main question and the CAMS offer varying solutions with all developing some convection but are different on storm mode and location of the storms. There are two themes from the CAMS and both make sense with this setup and may happen. Late afternoon or more likely evening storms should develop in far northern Minnesota which will be a bit closer to the larger scale forcing from the low/shortwave. The main threat from these storms will be large hail, up to 2" in diameter, damaging winds, and possibly a tornado. Further south closer to the warm front, severe storms will have a large hail threat like those further north but also have a greater chance for a tornado given a better chance for surface based storms. There are indications that an MCS or a line of severe storms may develop this evening with higher end damaging winds of 75 mph. This would be along and north of the warm front and include areas roughly south of US 2 from the Brainerd Lakes east into parts of northern Wisconsin. The bottom line is there is potential for a higher end severe weather outbreak and you need to monitor forecasts through the day into tonight. If you have outdoor plans, make sure you know where to go should storms develop. One thing that we didn`t mention with the storms is widespread heavy rainfall. The threat isn`t zero, but it`s also not expected to be a major issue. This is due to faster westerly deep layer winds which will lead to faster storm motions and be off the surface cold front which will minimize training storms. CAM guidance suggests rather localized rainfall amounts of 1-2", which is significant, but coverage is expected to be limited. Looking ahead, Tuesday and Wednesday will be dry for most with some showers possible in far northern Minnesota Tuesday. Highs will be 75-84 degrees Tuesday and cool into the upper sixties to mid-seventies Wednesday. There will be periodic chances for more showers/storms Thursday into early next week. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1252 AM CDT Mon Jun 24 2024 Fog will occur tonight in spots and has already been observed over portions of the Northland. We have the lowest visibility at KHYR/KHIB. The fog should lift quickly after 11 or 12Z. Focus will then shift to thunderstorm potential. A very warm, moist, and unstable airmass will develop through the day. The surface low pressure center will track well north of the International Border but a warm and cold front will affect the Northland. Some showers may affect portions of northern Minnesota by mid to late morning into early afternoon. These may be left over from the deep convection occurring in southeast SK attm. Of larger concern is later afternoon and overnight thunderstorms. Very warm temperatures aloft will move in during the day creating a cap which will at least for a time be tough to overcome. However, if convergence along the surface fronts and any weak shortwave can overcome the cap, severe thunderstorms will result. There is potential for high end severe thunderstorms will large hail to 2" in diameter and damaging wind to 75MPH. A tornado or two could also occur. Due to the uncertainty of if, where, when storms will fire, we mostly just added VCTS to the TAFS. Updates will refine timing but this will be a short term forecast issue. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 238 AM CDT Mon Jun 24 2024 Winds will be or become onshore today for most areas. Speeds are expected to be at or less than 15 knots today. There is a chance for thunderstorms this afternoon into tonight and some may produce large hail and winds in excess of 45 knots. Winds will switch to west or southwest tonight and increase late to 10 to 15 knots with gusts around 20 knots. The wind will increase further on Tuesday from the west and conditions may become hazardous for smaller vessels with gusts around 25 knots and a Small Craft Advisory may be needed. Winds will veer to north Tuesday night 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...None. && $$ DISCUSSION...Melde AVIATION...Melde MARINE...Melde