Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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996 FXUS63 KMQT 041946 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 346 PM EDT Sat May 4 2024 .KEY MESSAGES... -Rain overspreading the UP from west to east this afternoon/evening as a low pressure system moves through the area. -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 /THROUGH TONIGHT/... Issued at 312 PM EDT Sat May 4 2024 A shortwave trough moving through the Northern and Central Plains as noted on water vapor imagery will be propelling a cold front across Upper Mi this afternoon and evening, spreading showers from west to east across the fcst area. The leading edge of showers is into southern Houghton and western Iron counties as noted on the latest radar imagery as will continue to move through central Upper Mi from 20-00z and then into the eastern U.P. counties 00-03Z before exiting the eastern cwa by 09Z. Ridging and subsidence behind the shortwave and associated cold front will support drier conditions behind the front tonight and maybe some partial clearing over portions of the western U.P. later tonight. The moist low levels from the showers along with the prospect of partial clearing however could also support the development of stratus/patchy fog behind the front. Min temps tonight will generally range from the upper 30s west to the lower 40s central and east. && .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 /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 142 PM EDT Sat May 4 2024 VFR conditions will slowly deteriorate to low-end MVFR and possible IFR starting mid to late this afternoon at IWD and toward this evening (22Z-00Z) at SAW and CMX as rain overspreads Upper Michigan from west to east. Expect improvement back to VFR late this evening/overnight as drying and clearing occurs in the wake of a cold front. && .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 from 5 AM to 2 PM EDT Sunday for LSZ250- 251. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...GS AVIATION...Voss MARINE...GS