Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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727 FXUS63 KDTX 251936 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 336 PM EDT Wed Sep 25 2024 .KEY MESSAGES... - Dry for the remainder of the day, outside of a low chance (20%) for a shower, favored in the Thumb. - Sunny tomorrow with daytime highs in the mid-70s. - Next chance (30-40%) for rain showers will be Friday night into Saturday morning, favored along and south of M59. && .DISCUSSION... For the remainder of the afternoon and evening... Most locations remain dry, outside of isolated periods of drizzle or light rain showers favored over the Thumb, fueled by the pinnacle of the shortwave trough axis that swings over SE MI over the next several hours. Outside of this, we reside under non-favorable conditions for any sustained shower activity. Lapse rates remain shallow under only a couple hundred joules of CAPE. The extensive field of alto-cu will wane with the loss of daytime heating, but also with drier air filtering in from the northwest under increasing mid-level subsidence within the wake of the upper-level wave. The Great Lakes will stay situated between two upper-level lows tomorrow, the first over southern Quebec with the second deep into the Ohio River Basin. Upper-level confluence and continued support of mid-level subsidence in the wake of the shortwave will bring dry weather through tomorrow along with mostly sunny skies. Weak synoptic flow will bring very little change to the greater thermal field, however, the boost in insolation will bolster temperatures in the mid-70s. Attention will then turn to now-hurricane Helene, which is projected to arrive onshore around Thursday evening. The aforementioned Ohio Basin upper-level low will retrograde in response to the approaching tropical system, eventually phasing before gradually meandering back into the Ohio River Basin through the weekend. A ensemble heat map of the track density places the greater cluster of cyclone centers stalling out across northern Tennessee to southern Kentucky, with a smaller subset (10th percentile) encroaching into central Indiana/Ohio. This increases confidence that impacts to SE MI (in terms of QPF) will be on the lower side. The EPS/GEFS stamps reveal an initial spoke of enhanced moisture that pivots over Michigan Friday through Saturday morning, with moisture lingering over Michigan through the weekend. This will bring the chance for light rain, favored along to south of M59. Despite QPF chances trending south of the state line with the 00Z suite, the 12Z suite has trended rain chances right back right back over Michigan, which is also observed with the latest ML-models. Will continue to advertise a chance (30-40%) of showers Friday night into Saturday morning, favored along and south of M59. A strengthening pressure gradient in response to the approaching system will also bring some breezy conditions on Friday across far southern Michigan, with gusts likely ranging between 25-30 mph. Otherwise, temperatures stay relatively consistent through the weekend with highs in the mid 70s, lows in the 50s. Variance across ensemble members turns higher through Monday-Tuesday regarding speed and amplification of a trough that drops through the northern Plains, which will have implications on how fast the residual moisture from the post-tropical system exits the state. && .MARINE... Low pressure center is lifting just north of Lake Huron this afternoon with a northwesterly gradient now spreading across the lakes. Moisture has all pushed east of the region allowing for a dry mid week period with high pressure building in from the west. Winds will decrease 15 knots or less tonight out of the north before veering around to the northeast on Thursday. As the high pushes off to the east Friday, low pressure lifts north out of the Southeastern United States. The pressure gradient will be tightest over Lake Erie, and gusts of 25 to 30 knots appear likely Friday-Saturday morning. && .PREV DISCUSSION... Issued at 1238 PM EDT Wed Sep 25 2024 AVIATION... Daytime boundary layer growth has led to some clearing of the low clouds this morning. This trend will continue to some degree into the afternoon, although additional diurnal cloud development is likely. The increasing depth of the mixed layer will support cloud bases being predominately VFR by late this afternoon/evening. A push of drier air will arrive from the northwest tonight as high pressure expands in from the west. This will result in an overall clearing trend during the night. The weakening of the sfc gradient will also maintain light winds through much of the TAF period. For DTW/D21 Convection...Thunderstorms are not expected this period. DTW THRESHOLD PROBABILITIES... * High for ceiling at or below 5000 feet through this afternoon. Low this evening. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...AM MARINE.......AM AVIATION.....SC You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.