textproduct: Detroit/Pontiac

KEY MESSAGES

- Widespread light snow moves in from the west this morning resulting in accumulations of 0.5 to 1.5 inches by this afternoon.

- Below normal temperatures continue this week, with the coldest air expected Monday morning when wind chills drop to or below zero.

- Active weather pattern returns Tuesday with additional opportunities for accumulating snow, and even some rain (Tuesday night).

- Abnormally cold conditions settle back in by Thursday with lake effect snow chances through the end of the week.

AVIATION

Widespread light snow will continue to expand across SE MI through the mid-morning hours. Light snow will taper off in the late morning to early afternoon hours. Total snowfall accumulation will range between a half-inch, up to 1.5" by the early afternoon. MVFR cigs will accompany snowfall, along with periodic visibility restrictions down to IFR/MVFR. MVFR cigs likely hold on after snowfall tapers, however, dry air advection will work to lift and scour out some cloud cover late tonight and overnight. Confidence is much lower regarding mid- morning cig evolution as flow backs north-northeast. There is a weak signal for some Lake Huron moisture to traverse inland and combined with the potential for clear skies, can aid in the production of periodic low-level stratus.

For DTW...Snow is now moving across the terminal with peak snow rates between 10Z to 15Z. MVFR/IFR cigs and vis will be increasingly likely with these peak snow rates. Snow is expected to taper off between 12Z to 17Z. Some flurries may be possible in the afternoon.

DTW THRESHOLD PROBABILITIES...

* High for ceiling at or below 5000 ft tonight and Sunday.

* High as precip type being all snow Sunday morning.

PREV DISCUSSION

Issued at 359 AM EST Sun Dec 7 2025

DISCUSSION...

Initial wave of light snow along preceding isentropic upsloping is starting to work in from the west early this morning. The adjacent low pressure system and inverted trough axis should hold well to the southwest, over northern Indiana, and track east across the Ohio Valley. This setup will lead to minor accumulations by midday. Snowfall rates are not expected to be overly impressive given deficiencies in column saturation (lack of sustained supersaturation WRT ice through the DGZ) and weak dynamic ascent (gradual height falls). Still, isolated areas of brief moderate snowfall rates, capable of up to a third of an inch per hour cannot be ruled out, particularly between 10Z and 14Z this morning. Depth of the marginally saturated DGZ per forecast soundings (roughly 6-10 kft AGL) suggests sufficient nucleation and hydrometeor growth aloft to broadly produce SLRs above climatological averages, likely into the 13:1 to 15:1 range.

Model spread in QPF has decreased significantly as the event horizon approaches. Deterministic and ensemble agreement is shown for most areas receiving 0.05-0.15 inches of SWE. The NSSL/GSL CAMs were much more bullish (up to a half inch of liquid) have fallen into line. NBM (V4.3) 50th percentile has shown a decrease from most prior runs over the last 24 hours, now in the 0.5 to 1.5 inch range by 00Z this evening (90th percentile shows a range of 2 to 4 inches). The higher totals are mainly expected for the western portion of CWA (along/west of US-23), but portions of The Thumb could approach 2 inches once the reinforcing shot of cold air (upon a shift to NW flow) arrives later in the day. Period of shore-parallel winds poses the best chance for additional accumulations along the southern Huron coastline. Decreasing cloud cover and stronger anticyclonic flow from 1032 mb high pressure moving into the Upper Midwest leads to a chilly night. Lows in the mid single digits to lower teens (Metro Detroit), modified (warmer) by mild over-lake water temperatures (Superior/Michigan).

The arctic airmass combined with the last bit of gradient flow will cause early morning wind chills to approach 0F, possibly slightly below for areas west (clouds cleared out sooner). The lower tropospheric ridge passes over Lower Michigan on Monday leading to subsidence, but mid and upper clouds will be present as shortwave troughing aloft passes overhead. Highs will be capped in the 20s for most areas, some 10-15 degrees below seasonal normals.

Active pattern returns midweek with the next quick-hitting system arriving late Monday night. Model progs reveal a negatively tilted compact speed-max rolling into the Upper Midwest along a western CONUS longwave ridge. This VortMax digs into the state amidst reorientation of the sub-700 mb height field, southwesterly. This helps advect a plume of moisture into southern Lower heading into Tuesday morning. Precipitation type concerns have decreased given a cold onset, therefore snow is favored, even while temperatures lift above freezing Tuesday afternoon. Most of the snowfall should occur during the morning hours with the better accumulation potential further north, closer to the surface reflection. Latest guidance has a gradient of over an inch north of M-46 to perhaps a coating south of I-94 where temperatures have a higher chance of lifting several degrees above freezing by Tuesday afternoon.

The next Pacific wave arrives in quick succession Tuesday night into Wednesday with a warmer airmass. Temperatures could hold steady near the freezing mark overnight as the next round of precipitation gets underway. Latest sounding data shows higher confidence in snow at onset, switching over to primarily rain late Tuesday night into Wednesday morning once mid-level dry air strips out DGZ layer moisture during ensuing zonal flow. While most of the lower column will be saturated and sub-freezing, a lack of ice nuclei will be the main factor in the nocturnal change-over. The surface low pivots across northern Lower Wednesday morning with a trailing cold front which results in winds veering northwesterly. Some lake effect snow is possible Wednesday night.

Colder post-frontal airmass and occasionally favorable trajectories maintain lake effect snow chances through the end of the workweek. The next release of arctic air is set to arrive Friday night into Saturday, marked by 850 mb temperatures in the minus teens (Celsius).

MARINE...

Light winds around this morning as a ridge of high pressure has arrived over the Central Great Lakes. Weakening low pressure tracking through the Ohio Valley will bring widespread light snow this morning, trending toward more localized snow squalls over Lake Huron late in the day as 850 MB temps lower into the negative mid teens. Northwest winds gusting between 25-30 knots appear likely late in the day. However, winds then look to veer to the north- northeast fairly quickly and weaken Sunday night as high pressure quickly builds in for Monday morning. None-the-less, large waves of 6+ feet will build over the southern Lake Huron. Some of these larger waves will clip the nearshore waters of Lake Huron as winds veer around, and small craft advisories are in effect late this afternoon into into Monday morning for Outer Saginaw Bay and the nearshore waters of Lake Huron from Port Austin to Port Huron.

Brief southwest gales possible on Tuesday as low pressure tracks through the northern Great Lakes. A larger and stronger low pressure system is then on track to move through Lower Michigan Tuesday night into Wednesday producing widespread snow and even changing precipitation to rain over Lake St. Clair and Lake Erie. Rush of cold air behind the passage of the low will support strong northwest winds late Wednesday and Wednesday evening. Isolated, brief gusts to gales will be possible, but the pressure gradient quickly relaxes by Thursday morning.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 3 PM this afternoon to 10 AM EST Monday for LHZ421-441>443.

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