textproduct: Detroit/Pontiac

KEY MESSAGES

- Cooler today but still slightly above average.

- Light rain showers/drizzle will be possible tonight mainly south of M-59. Some freezing drizzle possible in the higher terrain of Oakland, Washtenaw, and Lenawee. Little to no ice accumulation.

- Wintry mix likely Friday with increasing potential for widespread freezing rain over much of SE MI. Ice accumulations of a tenth or two favored though some locales could approach a quarter inch. An inch of two of snow possible in the northernmost portions of the Thumb/Saginaw Valley.

DISCUSSION

A seasonable day in store for SE MI today as highs top out a few degrees above normal in the mid-upper 30s with high pressure passing overhead. Influence of said high wanes by evening as a weak shortwave rotates out of the upper midwest into the SW Great Lakes/Ohio Valley late evening-tonight. Main accompanying moisture plume and ascent occur southwest of the region, however areas mainly south of M-59 see just enough saturation to support drizzle development after roughly 8pm continuing through 3-5am. Temperatures during this window are forecast to range 31-36 with the potential 31- 32 temps holding over areas along/north of M-59 as well as along the higher terrain of the glacial moraine from the Irish Hills up through northern Oakland. In these areas, a window of light freezing drizzle is possible though given overall QPF very much on the lean side (only a few hundreths at most) no measurable ice accums expected.

Cold advection follows to start Christmas as high pressure sliding over northern Ontario sends a backdoor cold front across Lake Huron into SE MI. Southern areas (south of M-59) stand the best chance to see temps reach the lower 40s before falling below freezing in the evening. Northern areas are held in the lower to mid 30s given the earlier frontal passage. This colder air however sets the stage for more impactful weather with the next system arriving early Friday. Developing low pressure over the Midwest lifts a warm front toward southern lower MI with the elevated portions of the frontal slope arriving around 10-12Z. There remains good agreement across the model space that surface/near-surface temperatures will range from mid 20s to around 30 fed by persistent east-southeast flow at the base of the aforementioned northern Ontario high. Forecast soundings advertise +2-7C warm layer from roughly 3-9kft over the vast majority of SE MI, save for the far northern CWA (roughly north of M- 46) who's columns hold near or just below 0C. With the surface low track holding south across northern IN/OH and cool ESE flow blunting northward progression of the front, the trend has been for the surface warm front to fail to push further north of I-94 if not stalling over Lenawee-Monroe keeping temperatures for all areas north around or below 32 all day. Result is a very favorable setup for prolonged freezing rain for most of the area.

Areas of particular sensitivity and lower confidence in p-type at this time are the northern Thumb/Saginaw Valley who are looking to reside on the fringe of the elevated warm frontal slope. If warm advection is more robust (resulting from a more northerly frontal advance), more wintry mix (freezing rain-sleet) are favored vs a weaker push of elevated warm advection favoring more snow or snow- sleet. In a similar vein, these scenarios would likely impact the p- type over the southern third of the CWA with a stronger warm push favoring a transition to (liquid) rain vs staying freezing rain.

Anomalously moist airmass is drawn north by the low with the CMCE/GEFS/EPS all showing PW between 0.6-0.9", solidly above the 90th percentile for daily climo, with ensemble mean QPF ranging between 0.25-0.4". Currently, ice accumulations between 0.1-0.2" are most favored over the majority of the CWA, however should the colder trend hold (ie surface front fails to lift into SE MI) there is potential for some areas to exceed 0.25". Potential snow accumulations in the far northern portions of the CWA range 0.5-2" in the current forecast scenario. Given this forecast with sub- warning totals and lower confidence in higher end amounts (at this time), held off on any watch headlines with this forecast package.

Precipitation winds down during the evening Friday as low pressure advances across the central Appalachians. Low amplitude mid-level ridging fills in its place for Saturday bringing drier weather and modestly above average temperatures. Active pattern looks to continue to close out the weekend/start the new week as an energetic northern stream jet allows Pacific northwest shortwave(s) to track into the central CONUS/Great Lakes.

MARINE

A high pressure system will quickly move across the Great Lakes this morning and afternoon before washing out across the western Atlantic tonight. Influence of this high pressure will rapidly diminish wind speeds and gust potential through the morning and will maintain lighter winds through the day. A second high pressure system will then progress across the central Canadian Provinces, arriving over the James Bay by tomorrow evening. Wind direction will progress from northeast to southeast with the arrival of high pressure which will bring elevated wave heights along the Lake Huron shoreline. Small Craft Advisories may be needed through Thursday and Friday given favorable fetch increasing wave heights within the nearshore areas. The shift to east flow will also bring some stronger gusts with wind gusts ranging between 20 to 30 knots across Lake Huron.

PREV DISCUSSION

Issued at 1157 PM EST Tue Dec 23 2025

AVIATION...

Late evening observational trends indicate the scattered southern fringe of MVFR clouds gaining some traction while moving toward MBS from northern Lower Mi. The supporting backdoor front/pressure trough shows some weakening which may limit the southward reach of the clouds during the late night and in the morning. For now, the forecast brings MVFR into the DTW corridor off the Ontario peninsula as wind continues to veer north through east. The later timing requires monitoring for fog which is limited by the lingering surface wind and thickening high clouds. The arrival of high pressure helps dissipate the lower cloud component as it rolls quickly across the region in the afternoon. Coverage of VFR mid and high clouds remain substantial ahead of low pressure heading into the Ohio valley Wednesday night.

DTW THRESHOLD PROBABILITIES...

* Moderate for ceiling 5000 feet or less late tonight and in the morning.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory until 10 AM EST this morning for LHZ421-441- 442.

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