Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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543 FXUS63 KDLH 241751 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 1251 PM 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 335 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 /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1252 PM CDT Mon Jun 24 2024 VFR ceilings with mid/high level clouds aloft and diminishing showers continue for parts of central MN. Have periodic light SHRA/VCSH mention at KDLH/KHIB/KBRD through much of the afternoon, though coverage is becoming more isolated to scattered. The cloud cover is expected to lead to some hindering of the daytime heating, but a warm and cold front moving northeast out of eastern SD later today into tonight will still bring moist and unstable air to the area. Still some uncertainty on how much a capping inversion aloft will hold into this evening as it is a stout inversion, but short term model guidance still does hint at storm development along the warm front this evening somewhere across central MN, and a thinner area of convective development over north-central MN mid to late evening if storms are able to develop and then quickly track towards the east into late evening/early overnight. Any storms that do develop could produce large hail, damaging wind gusts, and potentially a tornado, particularly for the storms closer to the warm front. Amendments are likely as forecast trends through the afternoon hone in on when/where storms are more likely to form. For now, am maintaining VCTS/PROB30 mention for the periods of time when storm potential is highest. Any storms moving directly over a terminal could produce MVFR to IFR conditions. Some MVFR conditions, potentially IFR, are hinted at again by model guidance for tonight before skies clear out behind the cold front. Confidence in IFR conditions are 40% or less, with the highest potential at KDLH and KHIB. Some LLWS develops this evening into early tonight, mainly at KDLH/KHYR. Winds turn westerly later this evening behind the cold front, and turn gusty Tuesday towards the end of the current TAF period. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 335 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...Rothstein MARINE...Melde