textproduct: Detroit/Pontiac

KEY MESSAGES

- Cold weather will persist into the weekend. Winds will decrease tonight. Wind chills will be in the teens tonight and Friday morning.

- Accumulating snow is forecast late Saturday afternoon into Sunday morning, preliminary forecast totals are in the 3 to 6 inch range.

AVIATION

Lake effect snow showers/flurries wane late tonight into Friday with ceilings ranging between MVFR and VFR. Visibility reductions due to snowfall are becoming less likely as bands struggle to hold together across central Lower Michigan, but MVFR reductions are still possible should snow reach any TAF site. A combination of radar and model data suggests the remnants of the more consistent lake effect bands avoid the terminals. Amendments will be made accordingly to account for any low-level wind adjustments that could impact the trajectory of additional snowfall, mainly for MBS, FNT, or PTK. Satellite imagery showing pockets of clear skies will be temporary over any one location as subsidence drying occurs, but ceilings should fill back in. Westerly winds remain elevated into Friday with speeds in the 10 to 15 knot range, gusting into the 20s amidst persistent low-level instability/mixing. Lake effect snow potential decreases on Friday with more opportunities for VFR ceilings and continued gradient wind.

For DTW.. Some flurries remain possible, likely with minimal impact to visibility as the better lake effect bands should miss the terminal.

DTW THRESHOLD PROBABILITIES...

* Medium for ceiling at or below 5000 feet tonight and Friday.

* Low for crosswind threshold exceedence tonight and Friday.

* High for precipitation type as snow tonight.

PREV DISCUSSION

Issued at 300 PM EST Thu Nov 27 2025

DISCUSSION...

There will be a gradual departure of the upper low northeast of Lake Huron tonight into Friday. Moist cyclonic flow will however persist across much of Lower Mi through the night. This will at least sustain a low chance for some light snow showers/flurries. The low level flow will veer from WNW to NW during the night, which will largely focus the better lake effect activity outside of Se Mi. Despite some lingering gradient winds tonight, the airmass will be quite cold with 850mb temps down around -12C. This will warrant min temps into the 20s tonight and limit Friday highs to the lower 30s. Strengthening mid level subsidence on Friday will lower the inversion height. BUFKIT soundings suggest super saturation wrt ice within the -15 to -17 C layer, suggesting some flurries out of the diurnal strato cu field.

The mid level wave now over the Pacific Northwest will be the main focus for the weekend as it emerges in the lee of the Rockies early Saturday and lifts across the Ohio Valley/Great Lakes region Saturday night. The 12Z model suite agree that the wave will drive a region of strong mid level positive vorticity advection across Se Mi. Upper jet coupling is also shown to support a broad region of upper level divergence. Enhanced low level flow is also shown to transport a decent low level theta e axis/moist plume into the Lower Ohio Valley. System relative ascent in the mid levels is forecast to be quite good across Lower Mi late Saturday/Saturday night. These factors point to high probabilities for accumulation snow across all of Se Mi as the column has trended a little colder the last few model runs. Model cross sections indicate decreasing static stability, although it is quite elevated. While this all suggests some decent snow accumulation potential, there a few potential limiting factors. The strongest push of mid level isentropic ascent is forecast to be rather progressive. While moisture looks good for widespread snow, specific humidities in the 800-700mb layer are only forecast to rise to 2 g/kg (which raises some concerns that several model solutions may be high on QPF). Forecast thermal profiles indicate that dendrites may only be favored for a brief period, which would cut down on snow to liquid ratios. Both the GFS and ECMWF also have some indication that mid level drying may occur later in the period (especially across the eastern portions of the forecast area) which may also cut down on snow accums.

Among the array of probabilistic guidance, overall there is high probabilities for total snowfall in the range of 3 to 6 inches by Sunday morning, with at or below 50% for over 6 inches. Probabilistic data for 3-hour snowfall during the peak of the event is high for 1 to 2 inches, generally low for 3 inches or more. These factors and in coordination with WPC and surrounding offices will support holding off on a winter storm watch for this issuance and will allow for another model run to determine trends with this system. Aside from the typical uncertainty in snowfall amounts, there remains some spread in onset. Trends in probabilities are suggestive of snow expanding across the area between 2 and 6 PM Saturday, then persisting to some degree into Sunday morning.

MARINE...

Wednesday's low pressure system continues to push deeper into northeastern Canada allowing for a modest slackening in the pressure gradient particularly across western and southern Great Lakes. This trend has already been observed in Lake Clair with US ob sites no longer reporting gales and western Lake Erie trending toward consistent sub-gales. As a result, Gale Warnings for these waters have been dropped in favor of Small Craft Advisories. Weakening trend in gusts around the Thumb lag however favored to fall below gales late this evening which offers some potential for these warnings to be dropped early with the 10pm forecast update. Gradient maintains better strength over the open waters of Lake Huron given its closer proximity to the low supporting lower end gale potential (34-38kt) through tonight into early Friday morning. Eventually the northern edge of high pressure sliding across the Ohio Valley builds into the central Great Lakes over the course of Friday supporting a slow, but steady decrease in winds with sub 30kt flow developing by the latter half of the day.

High maintains light winds to start the weekend however southerly winds strengthen toward 20-25kts by Saturday night in advance of a new low ejecting out of the southern Plains and into the southern Great Lakes. Trends in the low track have shifted north, now favoring the low center moving northeasterly over the Saginaw Bay and central Lake Huron. Shift northward brings more chances for rain to mix in with snow for all but the northern areas. Winds turn to the northwest on the backside of the system second half of the day Sunday setting up a renewed push of arctic air over the region. Weaker low, compared to Wednesday's low, and a faster progression into northeastern Canada still lends to a less favorable gale setup. That said, there is remains modest potential (~30-40%) for a few hour period of entry level gales across northern/central Lake Huron Sunday evening/early night.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Gale Warning until 7 AM EST Friday for LHZ361-362.

Gale Warning until 10 AM EST Friday for LHZ363-421-441-462>464.

Small Craft Advisory until 10 PM EST Friday for LHZ422-442-443.

Lake St Clair...Small Craft Advisory until 4 PM EST Friday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EST Friday for LEZ444.

Low Water Advisory until 4 AM EST Friday for LEZ444.