Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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821 FXUS63 KMQT 121844 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 244 PM EDT Wed Jun 12 2024 .KEY MESSAGES... - Showers and thunderstorms expected (80% chance) between 9 pm and 3 am EDT tonight from west to east. - There is a slight risk (category 2/5) of severe weather for the western UP, with the main threats being large hail in excess of an inch and damaging winds in excess of 60 mph. There is a marginal risk (category 1/5) elsewhere, except for the far east. - Gusty winds expected Thursday along with lingering showers and thunderstorms. - Dry Friday and early Saturday before the return of showers and thunderstorms later in the weekend. - Warmer than normal temperatures frequent the forecast, with some areas approaching 90 for highs by next week. && .SHORT TERM /THROUGH THURSDAY NIGHT/... Issued at 244 PM EDT Wed Jun 12 2024 Early afternoon water vapor shows a couple of low-amplitude shortwaves embedded in fast midlevel flow over the north-central CONUS. The first is generating lift and a couple areas of showers along the WI/MI border and western Lake Superior, while an MCS is ongoing further south into the better instability over southern MN. No lightning strikes have been noted directly upstream as of yet, and with HRRR trending a bit drier/less convective for this afternoon, convection seems to be low probability and thus potential for thunder was capped at slight chance (<25%) for the remainder of the afternoon. Of greater concern is the late evening/overnight period tonight. Convection is expected to develop rapidly over northern MN this afternoon as steep (> 8C/km) lapse rates overspread the area. A classic loaded gun sounding in this area should yield intense storms assuming that forcing from the second aforementioned low-amplitude wave and attendant low-level boundary is sufficient, which it should be. The question for our area is to what extent these storms will hold together as they cross Lake Superior. The steep midlevel lapse rates should maintain MUCAPE of 1000-1500 J/kg across the western UP as the storms arrive. Wind shear is quite impressive both in the low levels, with a low-level jet of 30-40 kt overspreading the area, and in terms of deep-layer bulk shear which will max out between 40-60 kt. CAMs vary in their depiction of the incoming convection, but the HRRR has been relatively consistent in maintaining a broken line of organized strong/severe storms across the lake. Large hail in excess of an inch is a threat given the strong shear and steep midlevel lapse rates, and damaging winds in excess of 60 mph are also a threat despite the nocturnal period given the strong low-level wind field and likely maintenance of a respectable low-level mixed layer as well. SPC slight risk (level 2/5) in effect over the western counties. Storms should weaken with eastward extent as they outrun the better midlevel lapse rates and instability, but at least isolated strong/severe storm threat exists across most of the UP as SPC Marginal Risk (level 1/5) covers all areas except the eastern quarter or so. Main timeframe for storms looks to be roughly 01-06Z from west to east (9 pm-2 am EDT). && .LONG TERM /TONIGHT THROUGH TUESDAY/... Issued at 553 AM EDT Wed Jun 12 2024 The extended period will immediately start out this evening in the middle of a convective event as the first of two shortwaves continues its progression across the region. The question of intensity, though, still remains the biggest challenge. With decent 0-6 km shear values near 50 kts, thunderstorms will have a chance to maintain some strong to severe potential. But, the limiting factor in the Thu 00-06Z time frame remains instability. With MUCAPE values in the 250-500 J/kg range and CIN values well below -50 J/kg, storms will most likely diminish as they track across Upper Michigan into tonight with just some rumbles of thunder and lingering rain over the eastern third by Thu 09-12Z. Thursday, after the early morning round of showers/thunderstorms, it will generally be quiet through the morning. Nonetheless, strong west-northwest winds will follow in the wake of the associated cold front. And, then a few showers/thunderstorms could develop again during Thursday afternoon as the next shortwave provides a bit of lift during the best diurnal heating of the day. Severe weather isn`t expected, but cannot entirely rule out a few strong ones with some gusty winds and small hail. The main impact Thursday will be the winds outside of any storms, which will be strong as they mix down behind the aforementioned cold front. Widespread 25 to 30 mph winds are expected with isolated gusts in excess of 35+ mph per GFS/ECMWF ensemble means. After the winds diminish and rain tapers off Thursday evening, there will be a period of benign weather through Saturday morning due to ridging aloft. With the calmer weather will be slightly cooler, but still above normal temperatures in the 70s before the start of another warming trend through the weekend as guidance continues to trend toward mid to upper 80s Monday through Wednesday. Along with the heat, though, will be multiple chances for showers and thunderstorms starting Saturday morning as the next surface low approaches from the southwest. This low will track across the region over the weekend quickly followed by a broad upper low. Details with timing and strength remain low at this point, but the main consensus is a trend toward another hot period with active weather. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 144 PM EDT Wed Jun 12 2024 Main aviation concerns include timing and strength of potential thunderstorms, potential for low clouds following the storms at CMX, and low-level wind shear potential. There are two potential windows for thunderstorms. The first is roughly 18-22Z at CMX and 20-24Z at SAW. So far, no upstream convection is noted, and although modest destabilization is occurring, potential for the first round is too low to warrant inclusion in the TAFs. The second and more likely round is roughly 01-04Z at CMX/IWD and 03-05Z at SAW. Storms in this timeframe could produce strong wind gusts in excess of 40 kt as well as large hail to around an inch at CMX/IWD. Storms will be weakening with eastward extent but brief gusty winds and small hail still could occur at SAW. Vsby could fall to IFR/MVFR in any storms. After the storms, cloud bases will likely lower to MVFR/IFR late tonight at CMX before rising/scattering by around 12Z Thu. Low-level wind shear will be a concern at all sites tonight as a strong southwesterly low level jet moves overhead. Outside of storms and the period of possible low clouds at CMX, VFR conditions are expected. && .MARINE... Issued at 454 AM EDT Wed Jun 12 2024 Southerly winds mainly 20 knots and lower will persist across Lake Superior into this afternoon. But, as the high pressure is replaced by a series of disturbances, an uptick in southerly winds of 20 to 25 knots can be expected late this afternoon. In addition, rain and general thunderstorms will be possible across the far western portions of the lake by late morning, overspreading the remainder of the lake by this afternoon. Some storms could become strong to severe, though, late this afternoon/evening mainly over the far western portions of Lake Superior. Thursday, winds will become west- northwesterly behind a cold front with 20 to 25 knots (isolated to 30 knots) outside of any additional thunderstorm chances through the day. By Friday, winds will return to less than 20 knots with the return of high pressure where they will stay until early Sunday morning. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Thompson LONG TERM...TDUD AVIATION...Thompson MARINE...TDUD