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

Transition day in the upper levels as we go from split flow pattern into an amplified blocking pattern with Plains ridge in between coastal troughs. In getting there, we'll be presented with the only chance for precipitation for about the next week, and even that chance is only for the far southern locations mainly south of I94 tonight into Wednesday. Cause of this rain chance will be an upper low now over northern IL which will drift eastward in the weak flow on the south side of the split flow pattern while phasing with an elongated trough dropping out of the northern split and also reside weak troughing currently over the east coast. Models have been consistently showing a narrow axis of low level convergence around Lake Erie reaching into southern MI concurrent with mid level deformation north of the low and with a plume of enhanced theta e retrograding west around the north side of the low. Saturated layer in model sounding still up to around 10kft tonight but now extends further to around 15kft during the day Wednesday. Moisture does become more elevated with developing dry layer in the low level so chances of rain extending into Wednesday afternoon are low. High chance pop low QPF event for southern MI Tuesday night with less than a tenth of liquid for those that see any rain.

Heading into the weekend, the next longwave trough will come ashore the Pacific NW causing the Plains ridge to amplify setting up the blocking pattern across the conus. The expansive surface ridge to the north keeps easterly flow through the weekend allowing for only slowly moderating temperatures with the thermal trough holding over the region. So highs in the 60s will carry through the weekend before the ridge axis reaches lower MI allowing for southerly flow to return boosting temps back into the low 70s. With good amount of clear skies at night, favorable radiational cooling setup will allow lows to drop into the 40s each night.

MARINE

Modest east-northeasterly gradient winds persists over the central Great Lakes through Wednesday as an expansive 30.50 inHg high pressure system builds further east into Quebec. This sustains elevated on-shore waves for most of the waterways, therefore, a Small Craft Advisory remains in effect for all nearshore waters until Wednesday night. The diurnal boost to gusts has been muted compared to prior thinking as peak afternoon speeds remain below 30 knots. Still monitoring a Rex Block that should emerge overhead by Wednesday with the closed low positioning over the northern portion of the Ohio Valley. This alters the pressure and moisture fields, intersecting a stalled/deteriorated elevated frontal boundary. This may lead to some light showers over the far southern waterways (i.e. western Erie) by Wednesday morning. Wind speeds gradually start to decline through the latter half of the week as the pattern unlocks, and split flow returns aloft after the surface pressure gradient relaxes. Wave heights should recover accordingly, precluding the need for any extensions to the ongoing Small Craft Advisories.

PREV DISCUSSION

Issued at 1245 PM EDT Tue Sep 22 2026

AVIATION...

Moisture under a deep low level inversion led to some diurnal expansion into a scattered to broken cu field this afternoon. Low level moisture will remain more plentiful across the metro Detroit terminals today. This suggests high probabilities for longer duration of MVFR and/or IFR based clouds. Farther north, recent satellite trends indicate mixing of drier air into the low levels have scoured out the lower clouds. High pressure anchored over the northern Great Lakes today will sustain gusty east-northeast winds through the afternoon, gusts over 20 knots at times. Additional low level moisture advection is forecast overnight into metro Detroit. This suggests additional MVFR based cloud development is possible.

D21/DTW Convection...Thunderstorms are not forecast through the forecast period.

DTW THRESHOLD PROBABILITIES...

* Moderate in ceilings aob 5000 feet today and tonight.

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.