Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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389 FXUS63 KDTX 260718 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 318 AM EDT Thu Sep 26 2024 .KEY MESSAGES... - Mostly sunny today with daytime highs in the mid to upper 70s. - Next opportunity for rain showers (25-40 percent chance) arrives Friday night into Saturday for areas along/south I-96/696. - Lower chances for rain persist through the weekend with a rumble of thunder possible. && .DISCUSSION... An aggressive high pressure response is underway this morning as a 1017 mb surface ridge currently centered near the MN/WI/IA border exerts its influence further east across Lower Michigan. The statically stable airmass and accompanying subsidence is well evidenced in morning satellite imagery as a dense poleward cirrus plume struggles to make significant inroads beyond I-69 which will keep the majority of Southeast Michigan exposed to more sun than clouds today. A sparse diurnal cumulus field is then possible early this afternoon, but consensus RH progs are not conclusively representative of such. Forecast soundings do indicate slight moderation of the column today (both in the advective and adiabatic sense) which supports broad coverage of daytime highs approaching the upper 70s. This takes into account a much cooler start over the Tri-Cities (upper 40s) compared to the Metro area (closer to 60F) given uninhibited solar insolation for the former and cirrus obscuration for the latter. Confidence in a dry forecast continues to trend upward for the daylight hours Friday as Hurricane Helene accelerates north- northwestward across The Southeast before it rapidly deteriorates into a Tropical Depression. Latest solutions converge toward a forecast track that favors a sharp westward turn midday Friday leading to eventual residence over western Kentucky once the tropical wave engages an orphaned trough currently stalled over the Mid-Mississippi Valley. Such an evolution carries higher predictability in the core ThetaE plume holding south of the state- line, along with the associated heavy rainfall. Duration and magnitude questions persist regarding the extent of shearing rain bands that migrate into the southern part of the forecast area. Deflecting FGEN helps activate initial ascent/moistening over Monroe and Lenawee Counties Friday night before system-relative isentropic ascent reinforces shower activity along the northern fringe of the system. Will continue to advertise light QPF of a few hundredths of an inch Friday night into Saturday for the southern third of the CWA. Still expecting a more notable gust response Friday afternoon as east-northeast winds peak around 30 mph by late evening with the glancing LLJ core. Automated NBM PoPs for this weekend fell within the Chance range (25- 40 percent) up to I-69 which is probably a bit too aggressive for the northern edge. However, (light) rainfall still largely depends on the secondary and tertiary spokes of forcing aloft within an increasingly saturated environment as wrap-around Gulf moisture transport persists. Eventually, the propagation of a progressive Pacific wave dislodges the remnant system eastward Monday into Tuesday. Temperature readings remain on-track to peak a few degrees above climatological averages during this time with highs in the mid 70s and lows in the upper 50s (low 60s for the more urban areas). Next area of commanding high pressure builds into the Great Lakes behind a cold front for the middle of next week resulting in a transition to below normal temperatures and drier conditions. && .MARINE... High pressure will expand eastward across the region today resulting in northerly winds which will veer more northeasterly though the day while remaining below 15 knots. As the high pushes off to the east Friday, an area of low pressure will lift north out of the Southeastern United States and is forecast to stall over southern Illinois and Indiana late Friday. The pressure gradient between the high and approaching low will be tightest over Lake Erie, and gusts of 25 to 30 knots appear likely Friday-Saturday morning which would necessitate Small Craft Advisories. Winds will decrease heading northward toward Lake Huron but any shift north or south by the low will lead to a shifting wind field as well which will be watched for in the next 24-36 hours. && .PREV DISCUSSION... Issued at 1209 AM EDT Thu Sep 26 2024 AVIATION... A ridge of surface high pressure will build over Southeast Michigan tonight and Thursday along the northern flank of the Southeast United States upper level closed low. Very dry air in the low to mid levels will preclude low cloud. Instead looking at a long duration to the high cloud canopy over Southeast Michigan. Not expecting any fog Thursday morning at the Detroit terminals, with just a chance for some ground br at FNT and MBS at daybreak. Light northwest wind tonight becomes light northeast Thursday. For DTW/D21 Convection...Thunderstorms are not expected this period. DTW THRESHOLD PROBABILITIES... * Low for ceiling at or below 5000 feet tonight and Thursday. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...KGK MARINE.......DRK AVIATION.....CB You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.