Area Forecast Discussion
Issued by NWS Duluth, MN
Issued by NWS Duluth, MN
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889 FXUS63 KDLH 160552 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 1252 AM CDT Sun Jun 16 2024 .KEY MESSAGES... - Showers and thunderstorms this afternoon into tonight. Severe weather is not expected. Locally heavy rainfall could cause localized minor flooding in northwest Wisconsin tonight (~25% chance). - Scattered showers and thunderstorms are possible late Sunday afternoon through Sunday night (30-70% chance). A few storms may be strong to severe late Sunday afternoon and evening (~5% chance), with large to very large hail and strong winds as the main threats. - The threat for very heavy rain and flash flooding is increasing Monday through Tuesday (40-60% chance). Strong to severe storms capable of producing large hail and locally damaging wind gusts are also possible (15% chance) Monday afternoon into Monday night, with a 15% chance for severe weather again on Tuesday. && .DISCUSSION... Issued at 405 PM CDT Sat Jun 15 2024 Rest of today - Tonight: Warm air and moisture will continue surging in from our south the rest of this afternoon into tonight, bringing an area of an area of PWATs up to 1.6-1.8" (95th+ percentile of climatology) into east-central Minnesota into northeast Wisconsin. This anomalous moisture combined with energy from a shortwave trough passing through the Northland, will support a broad area of showers and embedded thunderstorms. The focus of highest rainfall with this band of precipitation will be in the aforementioned area where PWATs will be highest, particularly in NW WI. The HREF 24-hour localized PMM rainfall forecast paints some pockets of 1-1.5" of rainfall in Sawyer and Price counties through Sunday morning, while amounts drop off to ~0.75-1" for the remainder of NW WI, and generally 0.5" or less for areas in northeast Minnesota. This first round of rainfall will be relatively quick moving, so the chance for localized minor flooding is lower (25%) chance where the heaviest rain falls in NW WI due to already saturated soils and elevated streamflows from previous rainfall. A few short-lived, strong storms with small hail cannot be ruled out with the overnight into early Sunday morning convection in NW WI either given MUCAPE around 200-700 J/kg and about 20-25 knots of 0-6km bulk shear. Sunday: Precipitation diminishes/shifts east by early to mid Sunday morning, leading to a break in rainfall for a good part of the day as a very subtle shortwave ridge moves overhead. Substantial low-level warm air advection continues into Sunday leading to the potential development of 2000-3500 J/kg of MUCAPE by the afternoon hours, but will also result in the development of a strong capping inversion. Short-range guidance still varies a bit on how strong the capping inversion will be during the day, and depending on the rate of surface heating, could potentially be eroded in north-central Minnesota by mid- afternoon along a weak cold front where at least some weak forcing for upward ascent would be present. If the capping inversion were to erode, the large amount of instability combined with 0-6km bulk shear magnitudes of 40-50 knots would be supportive of conditional severe weather potential (5% chance). Large to very large hail (2"+) would be the initial threat with these storms if they do develop due to the shear/CAPE combination support supercell storm structures, with a transition to some clusters during the evening into the Brainerd Lakes to NE MN where the severe threat would be more in the form of large hail and locally damaging wind gusts. These storms would then push east of the Northland/diminish by the early overnight hours. Can`t rule out some locally heavy rainfall with these storms, as well. The other concern for Sunday will be abnormally hot temperatures. Highs in the upper 80s are expected in east-central Minnesota and northwest Wisconsin, which, when combined with low to mid-70s dewpoints, will produce heat index values in the low to mid-90s. While not quite to Heat Advisory thresholds, those who are sensitive to heat, especially without effective cooling or adequate hydration, will be most at risk for being affected by these very muggy conditions. Elsewhere in the Northland, expect low to mid-80s for highs with heat index values in the 80s. Late Sunday Night - early Monday: Another round of rainfall makes its way into the Northland late Sunday night into Monday morning as a strong low-level jet develops in association with another shortwave trough passing through the Northland. This initial overnight/morning convection would be elevated in nature just to the north of a west-east oriented stationary front across central MN into western/NW WI, but be capable of producing at least some large hail, with perhaps a few localized gustier winds making it to the ground level. Heavy rainfall and flash flooding also becomes a concern with this round of convection as storm motion looks to be generally west-east along the front, with the potential for storms repeatedly moving over the same locations with anomalously high PWATs to 1.6-1.9" once again. Depending on where exactly the stationary front and associated convection set up will dictate where this heaviest rain will fall as short- range guidance still varies a bit on how far north the convection sets up, some in southern parts of the Northland, and others even farther south across southern MN and western WI. It is Late Monday - Tuesday: Additional elevated instability develops north of the surface front that will now be migrating slowly northward again for later Monday into Monday night ahead of an ejecting surface low coming off the lee of the Rockies. This would lead to another threat for scattered severe storms, with large hail as the primary threat, but also some damaging wind potential for storms closest to the front. Into Tuesday, a cold front is likely to pass through on the back side of this system as the surface low ejects northeast, with the combination of CAPE/shear/moisture along the front conducive for severe storms, with damaging winds more so as the main severe threat as these storms form more of a line when passing through from west to east. Perhaps the biggest concern for Monday through Tuesday will be the heavy rain and flash flooding given repeated rounds of thunderstorms falling on already wet soils. A deep, saturated layer below the freezing level combined with PWATs likely around 2" or slightly more (near maximum of climatology) would produce very efficient rain processes and higher rainfall rates. Ensemble guidance even points to 24-hour accumulations of 2-3" from Monday evening through Tuesday evening, with even up to 4"+ in the Brainerd Lakes region (15-30% chance). This all said, it is becoming increasingly likely (40-60% chance) that flash flooding could occur Monday into Tuesday, so a Flood Watch issuance may be necessary as we get closer to that timeframe. This agrees well with the issuance of a Moderate WPC Excessive Rainfall Outlook (ERO) for Monday-Tuesday. For context, the last time we have had this high of an ERO risk was back on August 14th, 2020 when Brainerd to Grand Rapids had some flooding and several inches of heavy rainfall. There looks to be a brief break in precipitation by mid-week (Wednesday) as surface high pressure moves through, but another active and wet pattern could rear its head again heading into later this coming week into next weekend. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1252 AM CDT Sun Jun 16 2024 A messy forecast is in the works. For the rest of tonight, expect ceilings to continue falling into the IFR and occasionally LIFR range, especially lowest at DLH with some onshore and upsloping flow. There could be some temporary dense fog with visibility to 1/2SM or 1/4SM through early Sunday morning at DLH/HIB as several models suggest. Additional rain is expected to move through tonight, targeting HYR and DLH. There could be some embedded thunder as well (25% chance). Ceilings remain low through the morning with warm air and moisture advection in place, gradually lifting into the afternoon. Plenty of instability building aloft tomorrow may result in a broken line of thunderstorms developing in the afternoon and early evening. Strong to severe thunderstorms may be possible (5-15% chance), mainly bringing a threat for large hail but also possibly damaging winds. Ceilings trend VFR after possible storms pass Sunday evening. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 405 PM CDT Sat Jun 15 2024 Easterly winds will be less than 20 knots tonight into Sunday morning, but the longer fetch will briefly produce 2-4 ft wave heights from Taconite Harbor to Grand Portage early to mid Sunday morning. There will be a chance for thunderstorms tonight into Sunday, with the highest potential (30%) from the Twin Ports along the South Shore. Easterly winds on Sunday of around 10 to 15 knots turn light and southerly Sunday night and then northeasterly at 10 to 15 knots on Monday. Look for stronger south to southwest winds on Tuesday, with daytime gusts up to 25 knots to possibly produce hazardous conditions for small craft. Scattered strong to severe storms capable of producing large hail or strong winds are possible Sunday late afternoon and evening (~5% chance). Daily thunderstorm chances continue on Monday and Tuesday, with large hail and gusty winds as the main threats. 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...Small Craft Advisory from 6 AM to 10 AM CDT this morning for LSZ140-141. && $$ DISCUSSION...Rothstein AVIATION...JDS MARINE...Rothstein