Area Forecast Discussion
Issued by NWS Marquette, MI
Issued by NWS Marquette, MI
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834 FXUS63 KMQT 202018 AFDMQT Area Forecast Discussion National Weather Service Marquette MI 418 PM EDT Fri Sep 20 2024 .KEY MESSAGES... - Isolated showers and maybe a thunderstorm possible this evening east half. Patchy fog forming late tonight/early Saturday mainly central and east. - Extended stretch of well above normal temperatures continues through Saturday with highs mainly in the upper 70s and 80s. - Multiple rounds of precipitation possible through the first half of next week. Thunderstorms that do form are not expected to be severe at this time. - Temperatures around normal are expected to return next week. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 356 PM EDT Fri Sep 20 2024 Latest water vapor imagery and RAP analysis shows shortwave trough slowly progressing east through the east half of Upper Mi with the visible satellite imagery showing widespread diurnal cu across the U.P. Subsidence/mid-level drying behind this shortwave feature has resulted in dry conditions today over western Upper Mi. Central and eastern sections of the U.P. have seen a few isolated showers pop up in the vicinity of the mid-level trough axis and focused along outflow boundaries/lake breezes especially east of MQT in the past hour. This environment has also been more favorable for convection as lower to mid 60s dew points have led to MLCAPE values approaching 1000 j/kg central and east. However, build up of convection over the central and eastern U.P. has been largely inhibited by strong mid- level drying as noted on fcst soundings. Afternoon temperatures have been mostly in the 70s although a few lower 80s readings have been observed over the interior west. Other than some lingering isolated showers/t-storms over the east mainly early this evening, expect dry conditions to prevail as shortwave ridging and associated subsidence builds across the area from the west. Moist dew points in the upper 50s and lower 60s along with clearing of diurnal cu and light winds will likely lead again to patchy fog forming overnight into portions of central and eastern Upper Mi. Fog could become locally dense over eastern portions. Expect min temps generally lowering into the 50s with a few upper 40s readings possible over the typical cool spots of the interior west. && .LONG TERM /SATURDAY THROUGH FRIDAY/... Issued at 415 PM EDT Fri Sep 20 2024 Active weather pattern to begin the long term forecast as the sensible weather will be dictated by the evolution of multiple shortwaves passing in the vicinity of the Upper Great Lakes through early next week. Following Saturday`s well above normal temperatures, more seasonal temperatures return Sunday and beyond with highs in the 60s. While there is enough spread in the ensembles in the back half of the week to keep slight-chance (~20%) PoPs in the forecast for the eastern portions of the UP through the week, ensembles have continued to trend more dry with each ensemble suite run. Beyond next week, ensembles still favor ridging over the central CONUS, potentially leading to downstream high pressure over the Upper Great Lakes, which aligns with the CPC 8-14 day and 3-4 week precip outlooks which put the UP in a below normal precip pattern. Saturday will begin dry as weak surface ridging fills in behind the departed cold front. Mostly clear skies will allow highs to climb 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. However, if the WFO does break 80, it would be the most 80 degree days in any September, showing how unusually warm this stretch has been. The break in the clouds and precip will be brief however as a ~1005mb low will quickly jet along just east of the Manitoba/Ontario line, bringing showers and non-severe thunderstorms to the UP for overnight Saturday through Sunday along the low`s cold front. Recent runs have brought this low closer to the UP, which means that dynamic support for rainfall and thunderstorms should be better. No severe weather is expected though as HREF mean SBCAPE Saturday evening is only around 500 J/kg at most, though 0-6km shear at least looks modest at around 30 kt. Precip totals for this system look to be around a quarter of an inch, so nothing extreme, but welcome rainfall for a lot of areas that have struggled to get precipitation this month. Once the front departs Sunday night, the next feature to watch will be a 500mb trough that will exit the Four Corners region Saturday night. Ensemble spread is still high as to the impacts of this system as the trough could potentially interact with a Alberta Clipper-style trough that will be approaching the Upper Great Lakes at approximately the same time and there is disagreement as to the strength of each system and the track of the resulting surface features. Regardless of the exact solution, the NBM continues to trend more dry, with the western UP now strongly unlikely to see precip (PoPs less than 15%) and the eastern portions only have PoPs around 30%. If clear skies can verify Monday and Tuesday morning, interior low temperatures could get a bit cold, with bias-corrected MOS guidance suggesting lows in the upper to mid-30s in the interior west Monday and the widespread interior on Tuesday. Should mid-30s verify, there is a chance for patchy frost (~20%) those mornings. 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 GEFS showing preference for anomalous ridging over the central CONUS throughout the run, the CPC outlooks of less than normal precipitation will be on-track. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 358 PM EDT Fri Sep 20 2024 MVFR conditions have cleared out this afternoon. Expect VFR to prevail at most of the terminals through the period with the exception of some MVFR to IFR fog developing at SAW later tonight into early Sat morning. && .MARINE... Issued at 415 PM EDT Fri Sep 20 2024 Westerly wind gusts to 25 knots over the western portions of Lake Superior will gradually diminish tonight now that the cold front has completely passed over the lake. Localized surface ridging will keep wind gusts under 20 kt until Saturday evening, where another passing cold front will allow westerly and northwesterly wind gusts to 25 knots over the western half of the lake Sunday morning and up to 30 kt over the eastern portions of the lake during the day Sunday. This will force waves up to 4 feet along the shores of the Keweenaw Peninsula Sunday morning and waves of 4-6 feet over the east half of the lake throughout Sunday. Thunderstorms are possible with this front, but are not expected to be severe. Winds are currently forecast to be below 20 kt next week, but a couple of shortwave troughs approaching the Upper Great Lakes in the first half of the week could force a few gusts to 25 kt, but uncertainty is too high at this time to say exactly where, when, and how those gusts may occur. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... None. Lake Superior... None. Lake Michigan... None. && $$ SHORT TERM...Voss LONG TERM...GS AVIATION...Voss MARINE...GS