


Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
Issued by NWS Detroit/Pontiac, MI
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193 FXUS63 KDTX 232307 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 707 PM EDT Wed Jul 23 2025 .KEY MESSAGES... - A Heat Advisory remains in effect Thursday as high temperatures reach the lower to mid 90s with heat index peaking around 102 degrees. - The potential for thunderstorms continues to increase Thursday afternoon and especially Thursday evening. The strongest storms will be capable of 60 mph damaging wind, torrential rainfall, and localized flooding. - Continued warm and humid Friday with lingering or renewed shower/non-severe thunderstorm activity, particularly toward the southern Michigan border. - Additional rounds of showers and thunderstorms are likely for Saturday and Sunday as well. && .AVIATION... Return southerly flow is starting to increase across Southern Lower Michigan early this evening. This flow will usher in a wealth of near surface moisture. Some of the moisture may manifest in VFR cloud cover (4-5 kft) by daybreak and through the first half of Thursday morning. Otherwise, strong surface mixing will commence toward midday and will tap into quicker flow aloft in advance of an approaching frontal system - setting the stage for gusty conditions through the entire afternoon. As the front approaches and instability peaks, thunderstorm development is expected. Coverage will be predicated on the quality of deeper instability and the endurance of lower to mid level dynamic forcing with the approaching upper wave and the settling frontal zone - both of which will be on the decline. Consequently, coverage of thunderstorms may be somewhat limited. Main window for development across the Southeast Michigan airspace is currently in the 19-02z time slot. For DTW/D21 Convection...convection is expected to develop after 19z and wash east/southeast across the airspace in the 21-02z window. Coverage and character of the thunderstorms is still highly in question. Prospects for thunderstorms in the airspace are relatively high - but impacts at a single terminal are less confident. THRESHOLD PROBABILITIES... * Low for ceilings aob 5kft Thursday morning * Medium for thunderstorms in the D21 airspace after 20z Thursday && .PREV DISCUSSION... Issued at 357 PM EDT Wed Jul 23 2025 DISCUSSION... Mid Atlantic high pressure is reaching back to maintain influence on weather conditions in the Great Lakes today. A classic late July afternoon and evening is the result after highs in the mid to upper 80s with low humidity. All of that changes early Thursday as oppressive mid to upper 70s surface Td washes back over Lower Mi by afternoon. Upstream observations this afternoon indicate multiple reports of 80 Td in southern IL, likely agriculturally enhanced but still impressive. This also supports the Heat Advisory for Thursday afternoon and evening as high temperatures reach the lower to mid 90s and heat index peaks in the lower 100s. While inbound heat and humidity are fully supported by observations today, there are still questions regarding thunderstorm potential for Thursday. The inbound surface/boundary layer moisture adds confidence to model projections of a building instability axis across Lower Mi Tuesday afternoon as HREF mean surface based CAPE briefly reaches 3000 J/kg. Uncertainty lies in the opposing influence of capping low to mid level temperatures vs forcing brought by the current central Plains 500 mb circulation as it moves into the Great Lakes Thursday afternoon. As it stands at forecast issuance today, the 23/12Z DTX sounding this morning makes a strong case for the cap with 11 C at 700 mb and which is forecast to hold at least through Thursday morning. Satellite observations this afternoon also make a case for the 500 mb circulation that still looks well-organized but is forecast to weaken while shearing into the long wave ridge Thursday afternoon. It may end up just strong enough to erode the cap more convincingly with northward extent into central Lower Mi for scattered to numerous storm coverage becoming more isolated toward metro Detroit. The wind field is also more favorable for organized convection with northward extent as HREF offers 500 mb mean wind speed approaching 40 kts and a better bulk shear profile supporting a damaging wind threat. This may favor the Marginal Risk more toward the Saginaw valley and northern Thumb while not ruling out lower coverage toward metro Detroit. A prefrontal trough is showing up in HREF and regional/global model solutions as a focusing mechanism for afternoon storms in addition to the trailing cold front, both of which maintain a concern for heavy rainfall as an additional hazard through Thursday night. There are multiple scenarios for heavy rainfall and flooding, but not much definition on specific threat areas, as the storm environment builds PW toward 2 inches across the entire region. The potential for multiple outflows, the surface trough and cold front, all raise potential for training convective clusters as the pattern slowly progresses across Lower Mi through Thursday night. The 23/12Z model consensus then keeps the cold front progressive enough to move south of the Ohio border during the morning and especially before peak heating Friday afternoon. While the surface front settles south of the Ohio border, elevated portions remain over southern Lower Mi Friday night into the weekend. There is good consensus in the longer range models on an active elevated/nocturnal convective signal Friday night and Saturday night before the front is pulled back north into Lower Mi during Sunday. MARINE... The western edge of mid-Atlantic high pressure continues to govern Great Lakes conditions today and tonight. Meanwhile, a broad frontal zone will gradually shift eastward and increase gradient winds toward 15-20 knots by Thursday afternoon with gusts to 25 knots. SW flow funneling along Saginaw Bay will have the strongest gust potential, prompting Small Craft Advisories for the afternoon- evening. Dry weather is expected through Thursday for most of the area, with the exception of northern Lake Huron (especially north of Thunder Bay) which may get clipped by the ongoing thunderstorm complex over northern Wisconsin late tonight-Thursday morning. Shower and thunderstorm potential expands across all marine zones by Thursday afternoon as a hybrid upper level disturbance/cold front impact the area. Isolated strong to severe thunderstorms, characterized mainly by wind gusts over 34 knots, will be possible with the strongest storms. The front settles south toward the Michigan-Ohio border late Thursday night and stalls, maintaining shower and storm chances Friday as well. Periods of showers and thunderstorms remain possible through the weekend as well with a warm and unstable airmass settling overhead. HYDROLOGY... A hot, humid, and moisture rich air mass sets the stage for heavy rain producing thunderstorms late Thursday afternoon through Thursday night. There is lingering uncertainty on coverage and timing that makes it difficult to identify locations having greater threat. However, any strong to possibly severe thunderstorm will be capable of a quick 1.5 to 2+ inches of rainfall, which could produce localized flooding. If storms train over a particular area, more significant flooding is possible. Additional showers and thunderstorms are possible Friday, but rainfall amounts should remain under 1 inch, with the vast majority of additional activity toward the Ohio border. Higher coverage and amounts remain possible Saturday and Sunday as yet another upper level disturbance moves through the region. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...Heat Advisory from 11 AM to 8 PM EDT Thursday for MIZ047>049- 053>055-060>063-068>070-075-076-082-083. Lake Huron...Small Craft Advisory from noon to 10 PM EDT Thursday for LHZ421-422. Lake St Clair...None. Michigan waters of Lake Erie...None. && $$ AVIATION.....Mann DISCUSSION...BT MARINE.......MV HYDROLOGY....BT You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit.