Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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280 FXUS63 KDLH 181734 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 1234 PM CDT Tue Jun 18 2024 .KEY MESSAGES... - A few severe storms will be possible early this morning with damaging wind gusts to around 60 mph being the primary threat (20-30%) with the line approaching from the west. Elevated storms ahead of the line pose a threat for large hail (10-20%). - Another round of severe storms will be possible this afternoon as a cold front moves through the region. The main threats will be damaging wind gusts to 60 mph and large hail (20-40%), but an isolated embedded tornado or two (2%) cannot be ruled out. - Overall flash flood threat continues to diminish with lower QPF expected across the region. However, isolated pockets of 1-3 inches are still forecast across parts of Koochiching and northern St. Louis counties. The Flash Flood Watch has been trimmed to the north where the heaviest rainfall is expected. - After a short break, the pattern remains active with additional chances for rain and storms into the weekend along with a heavy rainfall threat. && .DISCUSSION... Issued at 459 AM CDT Tue Jun 18 2024 Low pressure was located over central South Dakota early this morning with a warm front stretching into southern Minnesota and central Wisconsin. Another area of low pressure was analyzed over eastern North Dakota with a stationary boundary stretching into northwestern Minnesota and northwestern Ontario. Showers and thunderstorms were moving across northeastern Minnesota in association with the warm front. These storms carry a risk of large hail to the size of half dollars along with heavy rainfall. A line of storms across northwestern Minnesota ahead of stationary boundary has been producing severe wind gusts across eastern South Dakota and northwestern Minnesota. As this line continues to push east early this morning, the threat for damaging winds will continue. A Severe Thunderstorm Watch has been issued for much of northeastern Minnesota with the exception of the Arrowhead through 9AM this morning. As the day progresses, the stationary boundary is expected to very slowly shift eastward. Additional waves of showers and thunderstorms are expected to develop along and ahead of this front across north-central and northeastern Minnesota. A very warm and moist airmass will move into the region ahead of the stationary/cold front characterized by dewpoints in the 60s and lower 70s and highs in the 80s. This will lead to building instability of 2000-3000 J/kg in areas east of the existing showers and storms. Effective shear remains around 35-40 knots with nearly unidirectional shear aloft favoring a linear storm mode through the event. CAMs keep convection over Cass, Itasca, Koochiching and northern St. Louis counties, which may limit the severe potential in those areas. In any case, damaging wind gusts to around 60 mph (30-40%) and hail to around 1" (20-30%) look to be the primary threats in any storms, although the linear nature of the storms may limit the hail potential. A few embedded tornadoes cannot be ruled out with SRH approaching 300 m2/s2 and along with decent speed shear in the lower levels. Heading into the evening hours, the front looks to be more progressive and will shift the showers and storms into northwestern Wisconsin with an overall diminishing trend by mid to late evening. A few showers may linger behind the front overnight, but any additional rainfall will be light. Speaking of rainfall, overall QPF for today continues to trend lower across the region. Most of the region will see around an inch or less of rainfall today with isolated higher pockets in stronger areas of convection. PWATs remain at the top of climatology for the day, so we may still overachieve in the rainfall department in spots. Heavier rainfall amounts of 1-2 inches plus is expected across parts of Koochiching and northern St. Louis County. This is the area that CAMs keep heavy rainfall in place through much of the day. This area will see the highest risk for any flash flooding today. With the lower QPF amounts elsewhere, have trimmed back the Flash Flood Watch to Koochiching, northern and central St. Louis, Itasca and northern Cass counties. Advisory level flooding will still be possible elsewhere given saturated ground and already high rivers and streams, but the overall flash flood threat has diminished. With highs in the 80s today across northwest Wisconsin and dewpoints in the 70s, heat indicies will be in the 90s for most of northwest Wisconsin. While this is not advisory level heat indicies, it will be very warm and muggy and uncomfortable for many. High pressure will then move through the Upper Midwest for Wednesday into Thursday bringing dry conditions with temperatures in the 70s. The pattern then remains active with southwest flow bringing another large system through the region starting Thursday and Friday with a warm front before a stronger low moves through for Saturday into Sunday. Ample moisture will move into the region from the Gulf of Mexico with PWATs rising to near the top of climatology once again. Instability continues to look anemic during much of this time period with the heavy rainfall threat being more of a concern. NBM probabilities have not changed much with chances of an inch or more remaining around 50 to 80% and chances for 2 inches or more at 30 to 50 percent. Given the rainfall currently occurring, many areas will be primed to be mainly runoff with saturated ground and already high rivers and streams. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1230 PM CDT Tue Jun 18 2024 A period of severe thunderstorms is expected across most of north-central and northeast Minnesota from 20Z Tuesday to 02Z Wednesday and produces hail to the size of a ping pong ball, heavy rainfall producing visibility down to 1SM and erratic wind gusts to 35 knots. The line of strong to severe thunderstorms moves into northwest Wisconsin after 00Z into 02Z, but weakens after 03Z as it trecks eastward. IFR ceilings are very likely ovenright and into early Wednesday morning through 12Z. Northwest winds and clearing skies accompany the post-cold front environment tomorrow 12-18Z. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 459 AM CDT Tue Jun 18 2024 Periods of showers and storms are expected over western Lake Superior today into this evening. Strong to severe storms will be possible this afternoon and evening with wind gusts to 50 knots being possible along with hail to around 1 inch in diameter. A cold front will work across the western part of the lake late this afternoon and evening with storms expected to end following the passage of the front. Winds outside of any storms today will be southerly at 5 to 15 knots with gusts to 20 to 30 knots, highest near the Twin Ports. These winds will also generate waves of 2 to 5 feet along the North Shore. Small Craft Advisories remain in effect for all of the nearshore waters for today into tonight. High pressure moves in late tonight and remains in place for Wednesday and Wednesday light leading to winds under 15 knots. For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...Flood Watch through Wednesday morning for MNZ010>012-018-019- 025-026. WI...None. MARINE...Small Craft Advisory until 1 AM CDT Wednesday for LSZ121- 144>148-150. Small Craft Advisory from 9 PM this evening to 1 AM CDT Wednesday for LSZ140>143. && $$ DISCUSSION...BJH AVIATION...NLy MARINE...BJH