textproduct: Detroit/Pontiac

KEY MESSAGES

- Extended stretch of seasonably cool conditions will exist thru the mid-week period.

- Aside from a low chance of rain tonight and Wednesday mainly south of I-94, dry conditions are expected through next weekend.

DISCUSSION

Mid-week conditions to remain governed generally by split mid level flow, featuring a broad upper high anchored over Ontario and a weak closed low drifting from the midwest today to the eastern Ohio valley by Thursday. At the surface, a strong 1028 mb anticyclone centered to the north maintains strong control over region, effectively maintaining a moderately firm low level east-northeast low level gradient. With little evidence of meaningful thermal advection, this ensures an extended stretch of below average temperatures. A more noteworthy gradient in high temperature where warmer conditions reside toward the north expected both today and Wednesday, owing to greater likelihood for higher cloud coverage to exist with southward extent. This gradient likely more pronounced Wednesday, as the aforementioned passing upper low works to draw a plume of higher moisture northward into southern sections tonight and Wednesday. Narrow axis of weak mid level deformation and low level convergence flanking the north side of this system will support a low end chance for light shower production overnight into Wednesday. A very dry ambient profile will certainly fight the northward advancement of measurable precipitation, leaving the highest probability for rain to remain concentrated along/south of the I-94 corridor. As the mid level trough translates eastward, upper heights climb accordingly for the end of the week downstream of higher amplitude upper ridging building over the Plains. This will establish an extended period of deep layer dry and stable conditions under strong subsidence as ridging dominates throughout the column. No precipitation is forecast through the upcoming weekend as upper ridging maintains control. Temperatures still edged slightly on the cooler side of average Thursday and Friday, before a moderating thermal profile under full insolation and increasing thicknesses lift highs back into the lower 70s by this weekend. Radiational cooling under clear skies will keep overnight lows generally in the mid to upper 40s. Next meaningful chance of rain unlikely to come until at least the middle of next week.

MARINE

Modest east-northeasterly gradient wind field persists over the central Great Lakes through Wednesday as an expansive 30.60 inHg high pressure system builds into Quebec. This sustains elevated wave action for most of the waterways, therefore, a Small Craft Advisory remains in effect for all nearshore waters. Expect another diurnal contribution to elevated gustiness, briefly exceeding 30 knots this afternoon. Additionally, upper level energy intersecting a stalled elevated frontal boundary could offer some sporadic light shower chances over the far southern waterways (i.e. Lake St. Clair and western Erie) tonight. A weak low pressure system should emerge over the northern portion of the Ohio Valley on Wednesday, altering the pressure and moisture fields. This could lead to slightly broader coverage of showers for the south-central Great Lakes on Wednesday while wind speeds gradually start to decline for the latter half of the week. An extension to the Small Craft Advisories may still be needed for a subset of the nearshores.

PREV DISCUSSION

Issued at 1152 PM EDT Mon Sep 21 2026

AVIATION...

Cloud cover has quickly eroded through the evening as evident on Nighttime Microphysics satellite imagery. Just a few bands of high cloud remain in place, although low stratus still lingers over northern Ohio. Winds are expected to veer slightly overnight into Tuesday morning, bringing this stratus deck back north and possibly clipping DTW/YIP/DET by about 14z. Prevailing ENE flow also becomes breezy during the afternoon, with gusts reaching 25-30 knots that peak over the Saginaw Valley. An upper low then slowly meanders into the southern Great Lakes by the end of the TAF period (06z Wednesday), bringing renewed moisture and thus lowering ceilings to the area Tuesday night.

D21/DTW Convection...Thunderstorms are not forecast today through Tuesday.

DTW THRESHOLD PROBABILITIES...

* Medium for ceiling at or below 5000 feet overnight into Tuesday. High Tuesday night.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory until 10 PM EDT Wednesday for LHZ421-422- 441>443.

Lake St Clair...Small Craft Advisory until 10 PM EDT Wednesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT Wednesday for LEZ444.