textproduct: Detroit/Pontiac

KEY MESSAGES

- Showers steadily shift offshore tonight and Saturday, then turning drier and warm next week.

DTW THRESHOLD PROBABILITIES

* High for ceilings at or below 5,000 feet this afternoon, low this evening and tonight, high tomorrow.

* Medium for light rain/melting snow mix this afternoon.

PREV DISCUSSION

Issued at 359 AM EST Fri Nov 13 2026

DISCUSSION...

A highly amplified omega pattern has settled in over the entirety of CONUS this morning, with Southeast Michigan positioned within the eastern longwave trough axis. The primary vicinity upper low eventually centers over Pennsylvania today, but its cyclonic wind field will preserve northerly flow throughout the day. This dislodges a pocket of colder Canadian air across the broader Great Lakes region, marked by 850 mb temperatures of 5 to 10 C below zero. Latest Lake Huron water temperatures are estimated around 10C, yielding a delta of 15-20C. In combination with favorable fetch, over lake instability supports the continuation of lake effect showers through the morning hours, with an expansion in coverage likely. Forecast soundings still support a wide range of precipitation outcomes given the underlying thermodynamics. The most likely time-frame for snow to mix in or become established as the dominant precipitation type is more likely to occur between 09Z and 15Z when the boundary-layer could support a nearly frozen parcel path. The main limiting factor that could favor more persistence for rainfall is the subtle backing of 850 mb/7 kft winds toward the NNW, introducing a disruptive drying component at the top of the saturation layer and the bottom of the DGZ.

As for model trends, local probabilistic guidance and the NBM have steeply declined in the spatial coverage of accumulating snow. Additionally, the areas that could see some accumulations, are now expected to be more limited, mainly downstream of The Thumb, and along the immediate southern Lake Huron shoreline. This requires more resilient convergence bands to persist, and then reorient with the subtle backing of controlling lower column flow. A survey of recent observations show a lag in cooling/drying which kept dewpoints above freezing for many locations into the early morning hours. At press time, no observing equipment were reporting snowfall. The sites to keep an eye on for today should be KCFS, KBAX, and KPHN. Should DGZ saturation, wet-bulb cooling, and supporting forcing properly align with sufficient snowfall rates materialize before temperatures diurnally rise, measurable snowfall still possible for the aforementioned locations, but this scenario is becoming less likely and primarily reserved for elevated surfaces.

And snow-composed shower activity transitions to rain or melting snow by late morning, and into the afternoon period as flow orients NNW. This shifts most of the residual lake effect activity further east, favoring the eastern portions of Huron, Sanilac, and (northeastern) St. Clair Clair Counties. Temperatures should come in 5 to 10 F below normal, in the lower 40s, but with sustained winds of 10 to 15 mph, wind chills will start out in the 20s for a few locations. Some lake effect precipitation will exists along the same corridor overnight.

A secondary upper low within the eastern flank of the blocking pattern will travel from north to south over the eastern half of the Great Lakes, in tandem with a similarly oriented mid-level speed max on Saturday. Lake-relevent trajectories should be more northwesterly at this time, which limits the viability of lake effect showers. The bulk of showers should again be limited to the St. Clair River vicinity. A couple degrees in thermal rebound could lift readings into the mid 40s Saturday, aided by weak warm advection.

The longwave ridge begins to move eastward into the area Saturday night, with the downstream inflection point overhead Sunday. 1030 mb surface high pressure builds into southern Lower Michigan with time. The synoptic ridge then bisects the forecast area Monday as surface flow weakens and flips southwesterly as the center of the surface wave tracks into eastern Ohio. A warming trend is then forecast through next week as the ridge feature anchors over southern Appalachia with milder Gulf-modifed air lifting in. A progressive and deepening Pacific wave unblocks the configuration mid-week, but is expected to pivot over the Upper Midwest, likely keeping the local area dry through the forecast window.

MARINE...

Northerly flow will hold today before backing northwest through the weekend. This prolonged northerly flow will support efficient mixing of some stronger winds aloft down to the surface as cooler air remains in place. This will produce wind gusts around 25 knots along with elevated wave heights along the Lake Huron shoreline, where Small Craft Advisories remain in effect. Additionally, near surface convergence has supported lake effect rain bands across the central and southern Lake Huron basins, which will persist into tomorrow. Breezy conditions will start to wind down on Sunday once high pressure builds in over the southern Great Lakes. This will bring a period of lighter winds along with dry weather early next week.

DTX WATCHES/WARNINGS/ADVISORIES

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

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