Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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787 FXUS63 KMQT 050856 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 456 AM EDT Sun May 5 2024 .KEY MESSAGES... -Dry conditions expected Sun/Mon, though mostly low winds and antecedent rainfall should broadly limit fire concerns. -Complex pattern setup for the midweek as multiple low pressure systems interact in the Midwest. Precipitation chances highest on Tuesday, but PoPs linger through the end of the week. Thunder potential highest Tuesday and Wednesday. && .SHORT TERM /TODAY/... Issued at 455 AM EDT Sun May 5 2024 Ridging/subsidence has overspread the UP early this morning in the wake of a shortwave and associated cold front. Thus, clearing has commenced, and radiational cooling is rapidly dropping temperatures across the west/southwest. As a result, forecast update will be issued to match developing trends. In addition, patchy fog may need to be added along the WI/MI border of that western sector as well, will continue to monitor. For the remainder of today, height rises will result in clear skies and plenty of sunshine and a pleasant day with high temperatures climbing into the mid 50s to mid 60s (coolest along Keweenaw and Lake Superior lakeshore). Ample mixing and heating will contribute to RH values just below the 30% mark along the WI/MI border, but antecedent rainfall will help to mitigate the threat. && .LONG TERM /SUNDAY THROUGH SATURDAY/... Issued at 346 PM EDT Sat May 4 2024 Sunday, 500mb heights begin to rise as ridging builds over the Upper Midwest, contrasted with troughs over Hudson Bay and the western CONUS. The ridge over the midwest will support a 1020mb high pressure settling over the Upper Great Lakes through late Monday. This will give the UP as a whole its driest stretch of the last few weeks with high confidence of no precip through at least early Tuesday morning. The main forecast concern will be how dry the airmass gets for Sunday and Monday, as efficient mixing and radiative heating under clear skies will allow RHs to fall. As the mixed layer rises to near 7kft in the interior west Sunday afternoon, RHs look to fall just below 30 percent. Using the NBM 10th percentile of dewpoints to calculate RHs Monday gives RHs falling to the lower 30s. With mostly light winds below 10 mph gusting to 15 mph expected (and CAMs even suggesting a lake breeze off of Lake Michigan) along with prior rainfall, fire weather concerns should be fairly low. The trough over the west becomes a bowling ball closed 500mb low as it emerges on the other side of the Rockies Monday, negatively tilting as it does. Height falls over the Northern Plains cause 500mb height anomalies over Montana and North Dakota to fall to -26 dam. This will support strong lee cyclogenesis, with the 12Z GEFS showing a near-980 mb low over the Northern Great Plains. Meanwhile, a near-120kt 300mb jet will be on the south side of the parent trough, with divergence aloft supporting cyclogenesis further south. Ensemble clusters bring this secondary low pressure into the Upper Great Lakes at roughly 990s mb, but there is considerable spread as to the interaction of these two low pressures, the timing and strength of each, and the implications of each variable. Ensembles vary significantly on thunder potential, with especially the 00Z Canadian ensemble suite having multiple members with ~1000 J/kg of SBCAPE in the afternoons of Tuesday and Wednesday, but other members have instability never overcoming any caps. Given the uncertainty, did not deviate from NBM PoPs, which bring up to 90% PoPs Tuesday afternoon for much of the UP, falling off by Wednesday morning to near 30%. PoPs never truly fall off through the week as enough ensemble solutions have low pressure stalling near the Great Lakes to warrant at least 15-25% PoPs into the weekend. Peeking beyond the next week, ensembles favor ridging over the western CONUS and troughing over the eastern CONUS, leaving the UP in a somewhat drier northwesterly flow pattern, reflected in each CPC precipitation outlook to favor below normal precip through the end of May. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 122 AM EDT Sun May 5 2024 Expect conditions to generally improve from MVFR to VFR early this morning over KSAW as the low-level cloud cover continues to leave the area. As for KCMX, some patchy FG looks to remain over the area until after sunrise this morning. KIWD could see some patchy fog as well; however, with low-level water vapor imagery showing very dry air overhead, we could see conditions remain VFR throughout the rest of the pre-dawn hours. VFR conditions remain over the TAF sites through the rest of today. && .MARINE... Issued at 346 PM EDT Sat May 4 2024 Behind showers today, high pressure settling over the Upper Great Lakes through Monday will cause winds to remain below 20 kt. Monday evening, developing low pressure systems over the Great Plains will compress the pressure gradient and cause northeasterly wind gusts to funnel near Duluth Harbor to 20-25 kt. As low pressure approaches Lake Superior Tuesday and into the midweek, wind gusts up to 30 kt are forecast. There is gale potential if the low pressure tends to be on the stronger side of guidance and the low tracks directly over Lake Superior, but probabilities are currently only around 20% for widespread, frequent gusts over the gale force threshold. Uncertainty in the forecast increases greatly into the later portions of the week, though winds are currently expected to be around 20 kt in the wake of the low pressure. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... Small Craft Advisory until 2 PM EDT this afternoon for LSZ250- 251. Lake Michigan... None. && $$ SHORT TERM...TDUD LONG TERM...GS AVIATION...TAP MARINE...GS