textproduct: Detroit/Pontiac

KEY MESSAGES

- Light rain overspreads SE MI this afternoon and evening.

- A much colder airmass arrives Thursday, triggering gusty north wind and lake effect rain/snow showers Thursday through Saturday. Minor wet snow accumulations will be possible in the Thumb.

DTW THRESHOLD PROBABILITIES

* Medium for ceilings at or below 5,000 feet late this afternoon- evening. High tonight into Thursday morning.

PREV DISCUSSION

Issued at 410 AM EST Wed Nov 11 2026

DISCUSSION...

Pseudo-zonal flow maintains benign conditions across the region this morning before a significant pattern shift arrives later today and carries through the late week. This shift is driven by a powerful Pacific jet streak working into western BC, causing downstream trough amplification from Hudson Bay all the way down to the Mid- Atlantic states. A shortwave embedded within NW flow over the Midwest first reaches the local area this evening with the attendant height falls and PVA ushering in deepening moisture with time. This brings a 40-60% chance of mainly light rain late afternoon and into this evening. A second shortwave originating from central Canada reaches the Great Lakes late this evening, marking the lead edge of an arctic air mass. As these two waves merge overhead, a deepening low will emerge east of the area and facilitate a period of prolonged northerly cold air advection Thursday into Saturday.

The initial cold front is marked by an uptick in convective rain shower coverage and gusty northeast winds Thursday morning. This precip works through from north to south with a brief lull before the inbound cold air induces enough over-lake instability for lake effect showers to kick off. Prolonged NNE sfc-850mb flow maintained over Lake Huron allows a multi-band character to emerge Thursday evening, reaching peak strength Friday morning as the next spoke of PVA arrives within deep cyclonic flow wrapping around the sprawling upper low retrograding into the northern Great Lakes. These bands will be predisposed to set up over the western/central Thumb and far eastern Thumb, including the Port Huron vicinity. Daytime temperatures hold in the 40s on Thursday with rain the predominant p- type, then melting snow gradually takes over Thursday night into Friday.

850mb temps fall to around -6C Thursday night, setting up delta-T over the lake of nearly 20C. Model soundings highlight 400-700 J/kg of lake induced CAPE and impressive boundary layer omega supporting localized moderate to heavy precip rates where the bands ultimately set up through Friday morning. Despite the colder air and heavier rates, ambient dew points in the lower 30s and near record high water temperatures (mid to upper 50s F) in the Lake Huron southern basin will result in significant melting of hydrometeors. Immediate lakeshore areas stay mild enough to see nil snow accumulation, but just a few miles inland WBZ heights falling below 1000 ft will offer potential for pockets of wet accumulations on grassy surfaces to around 1" by noon Friday. This is supported by 70-80% probability for minor accumulations in NBM and REFS ensemble data. A small handful of individual ensemble members and operational model runs advertise extreme snowfall amounts but these appear to be driven by unrealistic SLRs given the anticipated thermal profile and warm ground.

Synoptic flow backs to NNW Friday night, Saturday, and likely into Sunday which confines the lake effect banding to the northeastern Thumb. Elsewhere, subsidence maintains dry conditions and looks to eventually reduce coverage of lake effect clouds. The 850mb thermal trough keeps temps on the cool side of normal through the weekend - highs in the 40s and lows in the 20s/lower 30s. A period of rebounding heights ensues early next week as the longwave trough releases eastward. This favors dry and stable conditions with a gradual warming trend.

MARINE...

High pressure influence gradually exits the central Great Lakes today with weak/variable flow while the next low pressure system deepens and takes aim at the Ohio Valley. Winds pick up considerably over the waterways tonight as the system moves east. Expect modest- strong north-northeasterly flow, with a heightened wind and wave response. Latest model data continues to advertise a brief period of gusts to near gales Thursday morning for portions of Lake Huron, but still looks marginal enough to preclude any gale-related headlines. Small Craft Advisories are in effect for all nearshore waters for Thursday. Persistent troughing keeps winds elevated Friday, albeit with even lower chances for gales. Extensions will likely be needed for some of the small crafts, depending on how long the constricted gradient holds on. Potential exists for a waterspout or two during this time-frame as shower activity arises.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 1 AM to 10 PM EST Thursday for LHZ421-422- 441.

Small Craft Advisory from 4 AM to 10 PM EST Thursday for LHZ442-443.

Lake St Clair...Small Craft Advisory from 10 AM Thursday to 4 AM EST Friday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 10 AM Thursday to 4 AM EST Friday for LEZ444.