Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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067 FXUS63 KMQT 192049 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 449 PM EDT Thu Sep 19 2024 .KEY MESSAGES... - Extended stretch of well above normal temperatures continues through at least Saturday with highs mainly in the upper 70s and 80s. - A cold front brings scattered showers and a few thunderstorms tonight into Friday. Some stronger storms are possible in western Upper Michigan this evening. - Multiple rounds of precipitation possible through the first half of next week. Thunderstorms that do form are not expected to be severe. - Temperatures around normal are expected to return for next week. && .SHORT TERM /THROUGH TONIGHT/... Issued at 446 PM EDT Thu Sep 19 2024 Water vapor imagery and RAP analysis show troffing over the western U.S. with one well-defined mid-level low over southern Manitoba and a second just off of the central CA coast. Some elevated showers and a few storms have advanced into north central WI and western Upper Mi this afternoon ahead of the low over Manitoba. The mid-level ridge axis which was stationed over Upper Mi most of the week is getting pushed slightly se this afternoon although the attendant very dry air mass is still keeping the central and eastern U.P shower-free this afternoon. Afternoon temps thus far have reached into the mid 70s and lower 80s, coolest along the Lake Mi shore. Higher dew points in the 60s have resulted in a more unstable airmass south into north central WI where a cluster of elevated storms have formed at the nose of a theta-e ridge. Plenty of uncertainty regarding U.P weather for late this afternoon into tonight as the mid-level low over Manitoba lifts north and sends a mid-level trough and associated sfc cold front toward Upper Mi later tonight. High resolution models suggesting stronger convection and developing supercells now forming over southern MN in environment of SBCAPE values 1500-2000 j/kg will pose a severe risk into southern MN and western WI into early evening. These storms over southern MN and western WI are then expected to transition to a linear MCS tonight which moves east through WI. High effective shear of 40 kts or higher and CAPE values of 1000-2000 j/kg will favor the eastward movement of the MCS through WI tonight. Big question will be how this MCS affects moisture for supporting convection over the U.P tonight. A few of the CAMs suggest isolated to scattered showers and t-storms this evening over the west could potentially become more numerous in coverage into south central Upper Mi overnight if northern extent of MCS moving through WI clips this portion of the cwa. This will be something for the evening shift to keep an eye on. Increasing effective shear to 30 kts could support some stronger storms into the western U.P. this evening but severe threat will likely be limited by mostly elevated CAPE of 500-1000 j/kg. Look for min temps to stay around 60F tonight with increasing clouds and chance for showers. Patchy fog will be possible again tonight, especially central and east under moist southerly upslope flow. && .LONG TERM /FRIDAY THROUGH THURSDAY/... Issued at 400 PM EDT Thu Sep 19 2024 Active weather pattern to begin the long term forecast as a trio of shortwaves will pass in the vicinity of the Upper Great Lakes Friday through Tuesday. This will help keep more seasonal temperatures (highs in the 60s) and periodic precipitation chances in the forecast into the middle of next week. While there is enough spread in the ensembles in the back half of the week to keep slight-chance (~20%) PoPs in the forecast, ensembles have trended more dry over the past 24 hours of runs and anomalous ridging looks to reside over Manitoba and northern Ontario by the end of next week. Should this ridging persist, the pattern could dry out to end September, which aligns with the CPC 8-14 day and 3-4 week precip outlooks which put the UP in a below normal precip pattern. By Friday morning, the cold front associated with a 992mb occluded low over Manitoba will be draped over central-to-eastern Upper Michigan. This front will continue to drift eastward, though with the parent low only slowly drifting northeast itself, the front will take its time to push through. SBCAPE looks to be around 500-1000 J/kg along the front, so some thunderstorms are expected, but HREF reflectivity paintball plots show that the coverage of thunderstorms capable of 40+ dBZ will be sparse through the day Friday, so no severe weather is expected. While not everyone will be getting a soaking, the eastern 2/3 of the UP looks at least 50% likely to get a tenth of an inch or more of precipitation tomorrow with the 75th percentile of the HREF showing pockets of a half inch or more of rain. CAMs show some afternoon redevelopment of showers in the central UP, but otherwise, clearing skies behind the front should allow for highs to climb up to the mid-upper 70s in the west half, though highs will be closer to 70 in the east. Showers should exit the UP by midnight, and overnight lows fall to the upper 40s to upper 50s as a result. Localized ridging will allow for a mainly dry day on Saturday with highs back to around 80. While this is unseasonably warm, the NBM gives less than a 5% chance of breaking a record high at the MQT WFO that day. The break in the clouds and precip will be brief however as a ~1005mb low will quickly jet along the Manitoba/Ontario line, bringing showers and non-severe thunderstorms to the UP for overnight Saturday through Sunday along the low`s cold front. Mean daily precip rates with this system range between 0.2 to 0.4 inches, so nothing extreme, but welcome rainfall to some areas that are running well below normal over the past week and month. Beyond the weekend is a surprising amount of ensemble spread. 500mb height plots show a trough tracking from Colorado on Sunday towards the southern Great Lakes basin by late Tuesday but weakening as it approaches. Chances that precip arrives from this system are highest in the east (40-50%) than in the west (20-30%), but spread in solutions keeps the details rather muddy, though it is important to note that these PoPs are slightly lower than the previous NBM runs. Moving into the second half of the work week, the 12Z GEFS shows anomalous ridging building over the Northern Plains and Canadian Prairie with 500mb height anomaly reaching +20 dam over Manitoba by Thursday morning. Downstream high pressure of that ridge would tend to have the UP rather dry moving into late September, and with the potential for higher heights to persist (LREF chance of 500mb heights 580+ dam around 40%), the CPC outlooks of less than normal precipitation will be on-track. && .AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 133 PM EDT Thu Sep 19 2024 VFR conditions should prevail thru the evening hours at IWD/CMX/SAW. Southerly winds will prevail, gusting to around 20kt at IWD. Shra and some tsra will spread w to e across Upper MI tonight. Models indicate the coverage of showers is still uncertain, but expect isolated to scattered showers and t-storms reaching IWD late evening and then CMX closer to 04-05Z and SAW around 07Z with showers lasting approximately 2-3 hours before moving east. There is a potential for MVFR during any periods of heavier rainfall that may occur. At SAW, upslope southerly winds and shra should result in MVFR developing overnight and MVFR conditions could linger a few hours after sunrise before dissipating. Other than the possible lingering MVFR stratus/fog at SAW Fri morning, expect VFR conditions to prevail at the terminals on Friday. && .MARINE... Issued at 315 AM EDT Thu Sep 19 2024 Light winds of 20 knots or less today give way to southeast to southerly winds of 20 to 25 knots over the central lake this evening as a cool front slowly trudges from west to east today through Friday. This front will bring some showers and storms across the lake, with some storms possibly being strong to severe over the west (the main threats being strong, erratic winds and large, damaging hail). As the front moves eastwards with time, expect the severe threat to diminish, particularly by around midnight tonight EDT. While winds generally decrease to 20 knots or less across Lake Superior by Friday morning, the showers and storms continue along the front through Friday night. Weak ridging over the area keeps winds light Saturday before a cold front passes through Saturday night and Sunday from the west. Currently, we could see northwesterly winds gust to 20 to 25 knots behind the cold front over the western half of the lake late Saturday night and Sunday. In addition, expect to see some showers and a few thunderstorms with the front`s passage Saturday night through Sunday, although the convection isn`t a guarantee as some models do keep the lake rain- free (50 to 60% chance of occurrence). Another low lifting from the Southern Rockies may lift into the Upper Great Lakes around the Tuesday time period too and bring stronger winds and thunderstorms back across the lake, but uncertainty on this occurring is higher (around 30 to 40% chance of occurrence). && .MARINE... Issued at 400 PM EDT Thu Sep 19 2024 Ahead of a cold front passing over Lake Superior tonight, wind gusts out of the south and southeast are gusting to 25 knots over central Lake Superior and will persist through the evening. Wind gusts relax behind the front and will be near or below 20 kt for the remainder of the forecast, with the highest chances of exceeding 20 kt coming near a weaker cold front Saturday night and then depending on the track of a shortwave trough, another front on Monday. Waves will be 4-6 ft over central Lake Superior tonight, subsiding below 4 ft by Friday afternoon. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...GS AVIATION...Voss MARINE...GS