


Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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900 FXUS63 KDTX 150757 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 357 AM EDT Tue Jul 15 2025 .KEY MESSAGES... - Sunny and warm today with high temperatures around 90 degrees and heat indices in the low 90s. - Shower and thunderstorm chances begin Wednesday and increase Wednesday night through Thursday with potential for heavy rainfall. - A cold front sweeps through the area Thursday night followed by cooler and less humid air Friday and to start next weekend. && .DISCUSSION... Weak high pressure is centered over Lower Mi to start the day and begins more of an eastward move this afternoon and tonight. In the meantime, it combines with a plume of deep dry air aloft to ensure one more dry weather day across the region. Calm to light west wind surface through mid levels backs and increases from the south, and is expected to displace the forest fire smoke layer that had an impressive impact on temperatures yesterday. Full sun then helps readings reach guidance highs around 90 while surface Td lingering in the 60s keeps humidity in the moderate range. Heat index projections only tack on a couple degrees through peak heating. Progression of the larger scale pattern gains traction tonight as northern Ontario low pressure develops along the broad frontal zone reaching from northern Quebec to the upper Midwest and then into the central Plains. This system starts a weak process of low to mid level moisture transport from the Ohio valley and pulls the surface front back into Lower Mi late tonight and Wednesday morning. A hybrid short wave/MCV also moves up from mid MS/TN valleys to provide of boost of forcing, mainly south of the Mi border through sunrise. The lack of anything resembling a low level jet otherwise limits the northward reach of showers/storms in Lower Mi and reduces effectiveness of the mid level theta-e gradient through Wednesday morning. After that, the 15/00Z HREF advertises a more pronounced flare-up of surface based convection across SE Mi during afternoon peak heating as warm sector Td rises back into the 70s. The 70s Td footprint also outlines coverage of PW rising into the 1.5 to 2 inch range indicative of the moisture depth favorable for slow moving convection capable of heavy rainfall with a few moisture laden downbursts possible. The Wednesday phase of events in the Great Lakes helps set the larger scale moisture axis in place ahead of the Midwest frontal system by Wednesday night. Convection ongoing upstream late tonight runs the length of the front from western Lake Superior into the Rockies. This supports the 15/00Z deterministic models that offer broad agreement on similar cycles of surface based storms refiring each afternoon as the frontal system moves closer to Lower Mi. Timing is set for Wednesday afternoon activity across the Midwest to reach SE Mi late Wednesday night into Thursday morning, and then flare up again as the front moves through the region during Thursday. Convective clusters arrive with nocturnal timing affecting lower downstream instability but with an incrementally improved wind profile. This is highlighted by model 500 mb wind increasing from sub 20 knots Wednesday afternoon to around 35 knots Thursday morning, in line with the SPC marginal risk through 12Z Thursday. Model consensus on the frontal passage Thursday night, before midnight, is 6-12 hrs faster than the last few forecast cycles. Surface high pressure is then building solidly into Lower Mi by Friday morning with cooler and less humid air, but also giving way to the next low pressure system more quickly during the weekend. && .MARINE... Light, mostly southerly winds, continue into Wednesday supporting warm temperatures and increasing moisture. The next chance for showers and thunderstorms will enter Wednesday through early Friday as a series of upper-level disturbances and cold front pass over the Great Lakes. This brings the chance for some localized stronger wind gusts with any thunderstorm development, but otherwise winds remain light given the weaker pressure gradient in place. && .PREV DISCUSSION... Issued at 1200 AM EDT Tue Jul 15 2025 AVIATION... Predominately VFR conditions are expected through this TAF period with minimal clouds and light winds. High pressure moves directly over southeast Michigan and to the east tomorrow turning winds out of the south. Main item of note remains the presence of wild fire smoke near the surface that is bringing occasional periods of MVFR haze. The other item is, some models want to develop areas of fog or patchy fog across parts of southeast Michigan during the early morning hours. Confidence in a widespread fog is low, so will leave out for now and monitor trends through the morning hours. For DTW/D21 Convection...No thunderstorms expected this TAF period. THRESHOLD PROBABILITIES... * None. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ DISCUSSION...BT MARINE.......SF AVIATION.....AA You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.