Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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177 FXUS63 KDTX 220949 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 549 AM EDT Sun Sep 22 2024 .KEY MESSAGES... - Showers and thunderstorms late this afternoon through tonight. - More seasonable temperatures Monday through Wednesday with highest chance of precipitation Tuesday. && .AVIATION... Initial conditions marked by VFR ceilings (high cirrus) and unrestricted visibilities precede an approaching frontal boundary this evening. Top-down saturation commences with the approach of the front and it`s parent low pressure system. An eventual lowering to MVFR ensues with the lead wave of resultant rainfall late this afternoon and early evening (from west to east). Ceilings and visibilities degrade overnight with increasing potential for IFR restrictions (and perhaps LIFR). Did adjust the forecast to account for a period of IFR cigs/vsbys after midnight. Winds generally hold from the south with speeds around 10 knots today before veering toward the west (post-front) and then northerly by Monday morning. Ceiling improvement appears rather slow Monday, therefore opted to include IFR restrictions through 12Z in the absence of notable drying processes. For DTW/D21 Convection...An embedded thunderstorm or two are possible as rain overspreads the area late this evening with low confidence in location or timing specifics. DTW THRESHOLD PROBABILITIES... * Medium for ceilings at or below 5000 feet by 01Z Monday, then high through tonight and into Monday morning. * Low for thunderstorms from 22-07Z this evening. * Low for ceilings at or below 200 feet early Monday morning. && .PREV DISCUSSION... Issued at 313 AM EDT Sun Sep 22 2024 DISCUSSION... Higher amplitude upper ridging still fixated over the great lakes early this morning lends to one final day of well above average warmth today, before shortwave energy impinging on the region within general split flow affords a return to more seasonable conditions heading into next week. Early day conditions marked by thickening high based cloud as a deeper layer column stability holds firm under lingering ridging. Cloud cover provides a lower ceiling for prospective insolation potential relative to yesterday, but still sufficient to push highs into the lower/mid 80s within the background of a veering low level south to southwest flow. A lower coverage of high based light showers/sprinkles plausible by early- mid afternoon. Arrival of a higher magnitude theta-e plume attendant to the inbound shortwave now over Iowa sets the stage for a steady increase in rain potential from west to east between 20z and 00z late today. High likelihood of rain exists through tonight as forced ascent peaks with the passage of the surface reflection and cold frontal boundary. Potential for some embedded thunderstorms given quality of the moisture advection to diminish overall stability. Frontal zone eases into the Ohio valley Monday, as high pressure builds into the northern great lakes. This yields a cooler, yet still moist low level northerly flow to begin the work week. This maintains a high coverage of stratus, with a few spotty light showers plausible particularly across the thumb with an added moisture flux contribution off lake Huron. Resident thermal profile suggests highs edged on the cooler side of average - upper 60s/lower 70s. Attention midweek turns to behavior of a closed upper low currently drifting across the four corners region and a trailing northern stream wave/trough of north pacific origin. General consensus across the collective ensemble guidance shows the lead height fall center ejecting east-northeast with time, arriving locally Tuesday. Period of meaningful isentropic ascent along the existing elevated frontal zone offers an initial window for light rainfall production Monday night into early Tuesday. Highest probability exists Tuesday afternoon thru Tuesday night under strengthening convergence and cva as the surface low and warm front arrive coincident with the greatest height falls. NBM projected precip chances may ultimately prove too conservative given the environment, but worth noting a smaller subset of the ensemble suite, particularly within the GEFS and GEPS, deflect some of the higher quality moisture and forcing to the south. Potential for unsettled conditions to persist into Wednesday as higher amplitude troughing takes residence and looks to capitalize on continued moist low level conditions. Greater signal for drier conditions to take hold starting Thursday, as the large scale pattern again becomes high amplitude and blocked. This pattern projects a stretch of dry and pleasant conditions Friday into next weekend. MARINE... A strengthening inversion has and will continue to maintain some areas of fog across portions of Lake Huron through this morning, with improving visibilities expected by late this morning. Otherwise, an approaching low pressure system which will travel east across the northern Ohio River Valley into Lake Erie and Ontario today which will allow a cold front to push across the Great Lakes later tonight. Widespread showers with some embedded thunderstorms are expected with the passage of low pressure and the front. Wind direction will veer from the SSE to NNW/NNW in the wake of the front, where wind gusts increase slightly to around 20 knots. These slightly elevated wind gusts will persist through the day tomorrow. A second low pressure system will target southern Michigan Tuesday into Wednesday, bringing another round of showers and some elevated winds. HYDROLOGY... Showers with embedded thunderstorms are expected along a cold front from late this afternoon through tonight. Average rainfall will range from a half inch to three quarters of an inch. Given PWATs greater than 1.50 inches, locally higher amounts to 1.00 inch or greater will be possible. No significant flooding is expected. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Dense Fog Advisory until 10 AM EDT this morning for LHZ361>363. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....KGK DISCUSSION...MR MARINE.......AM HYDROLOGY....MR You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.