textproduct: Detroit/Pontiac

KEY MESSAGES

- Sunshine with temperatures climbing into the upper 50s to lower 60s tomorrow.

- Rain chances increase late Wednesday into Thursday, with an unsettled pattern continuing into the first half of the weekend.

- A much colder airmass arrives Thursday, triggering lake effect rain and snow showers late Thursday through Saturday.

DISCUSSION

Mild start to the week, followed by a cold and raw end to the work week.

An upper-level ridge axis over the central Great Lakes region this afternoon will slide east, allowing a weak, moisture-starved cold front/trough to cross Southeast Michigan Tuesday morning. Despite low-level winds veering to the west-northwest Tuesday afternoon, a dry antecedent airmass (mean RH around 30% in the 1000-500 mb layer) and early November insolation will support highs reaching around 60 to the lower 60s, aided by 925 mb temperatures warming to near 10 C across southern areas.

The primary focus for the medium-range period remains a significant pattern shift slated for the late week, as a full-latitude longwave trough develops over the eastern CONUS. Upper-level energy and associated 6-hour height falls tracking through the Pacific Northwest this evening will translate into the western Ohio Valley by late Wednesday, influenced and steered by a high-latitude upper- level wave/500 mb low progged to dig aggressively southward out of the Quebec/Hudson Bay region Wednesday into Thursday. A sharp cold front tied to the initial height falls will cross SE MI late Wednesday night into Thursday, abruptly ending the mild stretch. Behind the front, deep northwest flow will usher in an unseasonably cold arctic-sourced airmass, driving robust CAA that drops 850 mb temperatures to around -8 C by Friday. Periodic pulses of synoptic- scale ascent will traverse the region through late week via pockets of PVA tied to secondary shortwaves pinwheeling around the primary closed low.

Locally, the most impactful sensible weather will stem from the lake response. The arrival of the cold pool aloft will steepen low-to-mid- level lapse rates and foster deep convective mixing. With Lake Huron surface temperatures hovering around 10-12 C, over-water thermal differentials will reach around 20 C, generating lake-induced CAPE of 300-600 J/kg and inversion heights climbing well above 800 mb. This setup supports a prolonged period of lake-effect precipitation Thursday through Saturday. Thursday looks to feature the most widespread coverage, as brisk northeast low-level flow drives showers well inland. Local probabilistic guidance indicates wind gusts to 30 mph Thursday, making ambient temperatures in the 40s feel considerably colder. Given the thermal profile, daytime precipitation will favor a rain/melting snow mix late, transitioning primarily to wet/melting snow showers during the overnight and morning hours. As low-level winds back more north-northwest to northwest Friday into Saturday, the most organized banding will reorient toward the Thumb and eastern tier, though diurnal snow/graupel showers will still scatter inland under the core of the cold pool. There is some potential for light snow accumulation Thursday night into Friday should wet-bulb zero heights descend to 1,000 ft AGL or below. Guidance indicates a sharp thermal boundary, with marine influences holding wet-bulb zero heights at or above 2,000 ft along the immediate eastern Thumb shoreline. Probabilistic guidance suggests predominantly melting snow on paved surfaces, though chances (<30%) for minor accumulations exist and have been trending slightly upward. Specifics remain difficult to pin down this far out given the borderline boundary-layer thermal structure.

Heights slowly rebound over the weekend as sprawling surface high pressure over the western Great Lakes/Ohio Valley slides eastward. Large-scale subsidence will cap convective depths and shut down lake- effect activity, with 850 mb temperatures moderating toward 0 C by Sunday afternoon. Mostly clear skies and light winds Sunday night will provide ideal radiational cooling conditions, allowing minimum temperatures to drop back into the upper 20s to lower 30s.

MARINE

Stabilizing shortwave ridging has allowed high pressure influence to briefly build into the central Great Lakes this afternoon. Gradient flow responds accordingly, weakening and backing southwesterly. Troughing is then set to return late tonight into Tuesday as the next clipper tracks southeastward across Ontario. Its attendant cold front leads to a west-northwesterly wind shift with an uptick in speeds. The frontal passage should be dry frontal, with renewed improvements to mixing depths due to cold air advection and mild water temperatures. Cannot rule out an occasional post-frontal gale- force gust over portions of the northern Huron basin, but coverage and frequency appear too limited to warrant any gale-related headlines. A Small Craft Advisory may still be needed for The Thumb nearshores given a brief wave response. The progressive pattern continues Tuesday night into Wednesday as high pressure temporarily returns with weaker winds and lower wave heights. Progressive shortwave troughing aloft delivers a dose of showery weather Wednesday, followed by deepening surface low pressure over the Ohio Valley into Thursday.

PREV DISCUSSION

Issued at 1222 PM EST Mon Nov 9 2026

AVIATION...

Marginal MVFR / low-end VFR ceilings continue to mix out across the Thumb Region this afternoon, with MBS/FNT/PTK/DET now west of the remaining stratus. These ceilings will continue to erode through this afternoon, with high clouds streaming in from the northwest. Northwest winds will back this afternoon and evening, becoming southwesterly by/around 00Z as high pressure to our south crests the region. Late tonight through Tuesday, low pressure will track east across Ontario and into Quebec, sending a dry cold front across southeast Michigan. Along the front, winds will shift from southwest to west-northwest with FROPA expected between 09-12Z Tuesday. Some shallow boundary layer moisture lingers into the overnight hours, with some guidance hinting at a narrow window for shallow BR to develop. This narrow window will rely heavily on the departure of overnight mid/high clouds and how much time is left for an uptick in nocturnal cooling before/around sunrise.

DTW THRESHOLD PROBABILITIES...

* None.

DTX WATCHES/WARNINGS/ADVISORIES

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