


Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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348 FXUS63 KDTX 242229 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 629 PM EDT Thu Jul 24 2025 .KEY MESSAGES... - A Heat Advisory remains in effect through 8pm tonight. - Thunderstorms will impact portions of southeast Michigan late this afternoon through the late evening hours. The strongest storms will be capable of producing 60 mph damaging wind gusts, torrential rainfall, and flooding. - Continued warm and humid Friday with lingering chances for showers and non-severe thunderstorms towards the southern Michigan border. - Additional rounds of showers and thunderstorms are likely for Saturday and Saturday night. A few storms could be strong to severe. Torrential rainfall and localized flooding will remain a concern as well. && .AVIATION... Corridor of convective activity stretches from southern Lake Michigan to southern Lake Huron. The most active region has been around FNT, with several small scale cells perking about. This corridor is expected to settle south with the aid of an approaching frontal boundary. The storms upstream over Southwest Lower Michigan are expected to progress east through the evening hours - likely with a weakening component upon arrival to the immediate airspace. The surface flow will transition to west/northwest overnight - then flip to northeast with the better push of the post-frontal airmass. A muddled VFR to occasional MVFR cloud field should fill in across the area behind the frontal boundary. As drier air slow filters in from the north - ceilings will lift comfortably above 5kft - especially north of the Detroit terminals. The influence of the frontal zone may linger across the south - where additional shower and storm development is possible Friday afternoon. For DTW/D21 Convection...the northern reaches of the airspace continue to see weak activity with the focus shift south toward DTW amount 01z. Persistence of convection will be dwindling through the late evening as the storms move into a less favorable environment for organization. Expecting things to quiet down prior to midnight. THRESHOLD PROBABILITIES... * Medium for ceilings at or below 5 kft with evening storms, then high Friday AM. * Medium for thunderstorms this evening, with threat ending by 04Z. * Low for thunderstorms Friday afternoon. && .PREV DISCUSSION... Issued at 300 PM EDT Thu Jul 24 2025 DISCUSSION... Dewpoints in the upper 60s and lower 70s, combined with temperatures in the low to mid 90s have resulted in widespread heat index values of 100+ degrees. Thus, the Heat Advisory will remain in effect until 8pm this evening. Attention quickly turns to the ling of strong to severe storms moving east across mid-Michigan late this afternoon, ahead of a slow moving cold front. As this front continues to move southeast through the overnight hours, chances for convection increase. While daytime mixing has lowered our dewpoints and helped to thin our CAPE profile, this has led to a good environment with inverted-V soundings and ample DCAPE to remain concerned for strong to severe thunderstorm wind gusts. The main question remains is what the storm coverage looks like as we progress through the evening hours. High-res models have struggled to keep up with radar trends this afternoon, with most not handling the ongoing convection well. Based on current radar and satellite trends, do expect this ongoing line of convection across the Tri-Cities and Thumb regions to continue to move east and maintain its strong to severe intensity. Further south, additional development remains possible through the evening hours. Another complex of storms may also develop around the southern end of Lake Michigan and move east into our area later this evening and overnight. Torrential rainfall and localized flooding remain possible with any thunderstorm activity, especially if we see any training thunderstorms or high enough rainfall rates as storms move over urban areas. It is not out of the question that training thunderstorms could produce a quick 2+ inches of rainfall. As noted above, the cold front is slow to move through southeast Michigan tonight and into Friday morning. Mid-level flow becomes unidirectional along the front so the front will eventually stall out in the vicinity of MI/IN/OH border. Thus, lingering chances for showers and storms will persist across far southeast Michigan through Friday. There will not be a big airmass change behind this front, so temperatures likely stay in the 80s Friday with muggy conditions lingering. By Saturday, the stalled out front lifts back north as warm front in response to a shortwave lifting northeast across the Great Lakes region. This will bring back the uncomfortably humid air mass with dewpoints likely climbing into the lower 70s again. Chances for heavy rain and thunderstorms return as well, a few thunderstorms could be strong to severe on Saturday. There are some indications within the medium-range guidance and probability space for an increased potential for an axis of heavier rain to develop Saturday evening/night as the main shortwave moves through. There is low confidence in the positioning of this axis of heavier rain or training thunderstorms, but the potential is there for an axis of 2 inches of rain (or higher). Sunday we should see a break in the active weather, but the warm and mugging conditions with periodic chances for showers and thunderstorms return next week. MARINE... Most immediate concern for the marine forecast is a broken line of strong to severe thunderstorms moving across Lake Huron. These storms will be capable of wind gusts in excess of 34 knots, frequent cloud to ground lightning, and erratic waves. Storm chances for areas south of Lake Huron exist later this evening/overnight as a second line of thunderstorms tracks west to east across the area. Similar hazards are in play for this line of storms. Expect storm chances to wane overnight as the second line of storms departs, with a cold front dropping south through the area early Friday morning and shifting winds to the north. The front settles near or just south of the Michigan state line on Friday, which ensures a mainly dry forecast for most of the area and light northerly winds. A broad area of weak high pressure fills in but will not do much to cap storm chances this weekend as the front lifts back to the north and brings warm/unstable air back into the area. The overall wind field stays below any longer-fused headlines, but thunderstorm winds may again exceed 34 knots with storms this weekend. The warm and unstable pattern persists into early next week before shifting to a northwest flow pattern mid-week. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory until 8 PM EDT this evening for MIZ047>049-053>055- 060>063-068>070-075-076-082-083. Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....Mann DISCUSSION...JA MARINE.......MV You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.