textproduct: Detroit/Pontiac

KEY MESSAGES

- Morning showers and storms are likely to remain sub-severe, but will be capable of producing heavy downpours and localized ponding.

- Numerous showers and thunderstorms are likely this afternoon and evening. The strongest storms will be capable of producing isolated wind gusts around 50 to 60 mph and small hail. Isolated flooding is also possible through this evening.

- Dry conditions are favored Thursday and Friday with a warm-up expected Friday into Saturday.

- The next chance of thunderstorms arrives Saturday, with some strong storms possible.

DISCUSSION

A moist environment within a sfc-850mb theta-e tongue has supported blossoming elevated convection overnight with radar derived rainfall estimates so far reaching 0.75 to 1.25" in the heaviest slow-moving storms. These have been driven along the nose of a weak LLJ beneath ascent tied to upper jet entrance region. The LLJ weakens and upper jet forcing eases east through the mid morning hours which should bring a relative lull in precip coverage mid to late morning. The plume of instability holds in place through the day to continue to support convective chances, gradually becoming surface based with 1000 to 2000 J/kg SBCAPE this afternoon. A weak cold front working into the area should be sufficient to trigger numerous showers and storms this afternoon and evening. Weak flow through the column limits deep layer wind shear to around 20 kt which keeps storms disorganized into a pulse or multicell mode.

The probability for severe weather is low in this setup but precip loaded downbursts will be a threat, capable of isolated wind gusts of 40 to 60 mph. Small hail is also possible in the strongest updrafts. Compared to recent similar setups, PWAT will be slightly lower at around 1.50" but still supportive of localized heavy downpours - especially given slow storm motion around 15 to 25 mph. SE MI is highlighted in a Marginal Risk for severe weather and excessive rainfall today with the greatest threat expected between 2pm and 10pm. Highs in the lower to mid 80s with dew point near 70F maintains a muggy feel through the day.

Confluent northwest mid to upper flow follows passage of the trough axis, allowing the cold front to gradually settle south of the area on Thursday. Post-frontal thermal advection will be relatively weak, just a degree or two drop in 850mb temp, but dew point will settle into a slightly more comfortable range in the mid 60s. Can't rule out a stray lake boundary triggered shower in the far southeast where some weak instability lingers into tomorrow afternoon, but the subsidence in place and strong dry advection at 700mb should support overall dry conditions and clearing skies.

Relatively high forecast uncertainty exists for the Friday period as a ridge attempts to amplify overhead but contends with one or more embedded shortwaves working beneath it. The bulk of shortwave energy arriving initially will be generated by convection over the Northern Plains tonight - the strength and timing of this activity will influence moisture return and the cloud/precipitation forecast Friday. There is a camp of solutions, dominated by the Canadian ensemble, that produce a stronger trough over the Canadian Prairie and Great Plains that appears to propel this shortwave activity in to offer a higher chance for precip. For now, given the governing ridge setting up and dominant signal for lower precip chances among ensemble solutions, no reason to deviate from the NBM forecast that carries just a slight chance of showers and storms.

Stronger signal exists for a low pressure system to track through the region on Saturday in response to the aforementioned Plains trough taking on a negative tilt as it pivots over the upper Great Lakes. This period bears watching for stronger storms given higher wind shear and potential for organized forced ascent along the height fall center. Assuming the warm sector passes overhead during daylight hours, highs in the upper 80s and lower 90s are achievable. Chances for additional showers and storms carry into the weekend as low amplitude prevailing flow offers opportunity for several disturbances to pass over the region.

MARINE

A weak surface low/trough drifts over Lake Huron this morning while gentle winds organize out of the SE. This draws more humid and increasingly unstable air into the region while the governing upper low tracks across eastern Ontario into western Quebec. The combination of forcing and instability ensure periodic thunderstorms this afternoon and evening, with later rounds tied to the passage of the system's cold front. Ambient dynamics are rather weak which should keep prevailing conditions below Small Craft Advisory criteria, but locally higher winds/waves are possible with some stronger storms that might develop. Shortwave ridging slides east Thursday allowing surface high pressure to build in from the Upper Midwest which facilitates mainly dry conditions across the waterways. A more robust low moves in late Friday into Saturday with renewed potential for showers and storms.

HYDROLOGY

Scattered to numerous showers and thunderstorms are forecast today, mainly during the afternoon and evening. Storms will be relatively disorganized, but with humid conditions and slow storm movement east at around 15 to 25 mph, storms will be capable of producing torrential downpours. Localized areas may receive near 1 inch per hour rainfall rates, with isolated rainfall totals ranging from 1 to 3 inches possible. The higher totals will be most likely for any areas that see training or repeated thunderstorm activity. Isolated instances of flooding of urban areas, small streams, and otherwise poorly drained areas will be possible, especially if storms track over locations that already received heavy rain early this morning. The main threat for flooding will be between 2pm and 10pm.

PREV DISCUSSION

Issued at 1236 AM EDT Wed Jul 9 2025

AVIATION...

A warm front lifts across the area sparking scattered showers and possible thunderstorms. Scattered showers and possible thunderstorms will last through the morning until around 11-12Z and focused from FNT south to the southern metro terminals. Will still see predominately VFR skies through tonight, but occasional MVFR conditions will be possible with any activity that passes over terminals. It's possible showers linger after 11-12Z, but the greater chances for more showers and thunderstorms is expected early this afternoon associated with the cold front. Have maintained PROB30 groups for this potential. VFR conditions follow thunderstorm chances this evening into tonight.

For DTW/D21 Convection... There will be a low chance for thunderstorms with shower activity through the morning hours. Greater thunderstorm threat comes by around 16Z and through the afternoon. Isolated severe weather will be possible.

THRESHOLD PROBABILITIES...

* Low for thunderstorms through this morning and again this afternoon.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...None.