textproduct: Detroit/Pontiac

KEY MESSAGES

- Bitter cold temperatures for the weekend into Monday. The coldest period will be Saturday night and Sunday morning. Expect wind chills to range between -15F to -10F by Sunday morning.

- Higher-end chances (50-60%) for light snow overnight. Snow accumulations will range from trace amounts up to a half-inch. A second chance (30-50%) for snow returns tomorrow afternoon and evening from I-94 south. Up to an additional half-inch will be possible.

- A dramatic warmup is then forecasted Tuesday-Thursday next week, as temps likely push aoa 40 degrees, setting the stage for potential rain.

DISCUSSION

For the remainder of the afternoon and evening... A stratus deck has filled back in across SE MI which will sustain into the overnight hours under an established low-level inversion. Overnight, a strong PV anomaly now extending into northern Minnesota will continue to drive south into the northern Great Lakes. This will push a cold front over Michigan through the morning hours and will bring the chance for light accumulating snow. Both the shallow moist isentropic ascent up through 750mb ahead of the front and shallow convergence along the cold front itself will provide forcing for light snow chances overnight. Snowfall totals will range from trace amounts, up to a half-inch, with snow chances ending by 12Z.

Strong cold air advection behind the front will bring decreasing temperatures through the day and will maintain a shallow but stark mixing layer which will produce wind gusts on the order of 20 to 30 mph. Cold temperatures in conjunction with breezy conditions will produce wind chills around 0 degrees to the low single digits across SE MI by the afternoon hours. Flurries will remain possible given the shallow but strong lllr and sufficient 0-1km moisture, but moisture depths are too shallow to sustain accumulation. The one exception will be around I-94 and locations south in the afternoon and early evening as an upper-level wave rounds into the Ohio Valley. The northern precipitation shield of this feature has low- end chances to clip southern Michigan which can bring light accumulations up to a half-inch. The updated forecast will hold Pop values to 20% up around the I-94, increasing to 50% near the border.

The upper-level wave will continue to deepen across the Great Lakes through the weekend which will reinforce this significant cold air intrusion. While the magnitude of the wind speeds are not out of the normal, ensemble v-wind anomalies highlight the rarity of a sustained due-northerly fetch for mid-December, maximizing cold air transport. 850mb temperatures drop to near -20C and 700 mb temperatures to -26C by Sunday morning. Temperatures drop to around the 0 degree mark Sunday morning with wind chills ranging from -15F to -10F. A cold weather advisory will be under consideration for parts or all of the cwa for Sunday morning. Temperatures remain capped in the 20s for a high on Sunday, returning into the single digits overnight, with a return back into the 20s by Monday. Overall, expect temperatures to run roughly 20 to 25 degrees below normal through Monday.

A Pacific wave will arrive onshore by the midweek which will deepen east of the Rockies before arriving across Michigan Thursday. Flow will back to the southwest in response to this wave, bringing temperatures back to near normal values Tuesday and likely above normal Wednesday-Thursday, with Thursday having the best chance to see temperatures peak aoa 40 degrees. While near the end of the forecast package, ensembles are showing moderate convergence highlighting moderate ivt ahead of a cold front on Thursday, bringing increasing confidence for rain showers.

MARINE

Southwesterly winds will be slowly increasing through the rest of the day and overnight ahead of an approaching arctic front tied to a low pressure system that will track across Ontario tonight. Winds will turn westerly overnight behind the front and will increase with gusts up to 30 knots possible across parts of central and southern Lake Huron. Winds will remain elevated in the upper 20 knot range through Saturday with the coldest of the arctic air arriving late Saturday and overnight which will cause a boost to the winds to around 30 knots across the southern basin. At this time, guidance suggests we'll stay below 35 knot gales but that will be something to watch in the coming days. A long duration Small Craft Advisory is in effect this evening through Monday morning to account for this cold unstable airmass and period of wind and waves. The cold airmass and elevated winds will also lead to potential snow squalls and freezing spray as well.

PREV DISCUSSION

Issued at 1148 AM EST Fri Dec 12 2025

AVIATION...

Sfc high pressure over Se Mi and dry ambient airmass has caused a general erosion of the stratus across much of Se Mi. Developing southwest flow in advance of an approaching cold front will focus the stratus deck across the MBS and FNT region this afternoon. Forecast expansion of the low clouds late this afternoon evening will increase chances for low cloud re expansion across the remainder of the terminals later in the day. The cold front is forecast to track across Se Mi between 06Z and 12Z Saturday morning. Frontal convergence and enhancement off Lake Mi will support an area of light snow showers along/in advance of the front. The overall brief period of stronger forcing will keep snow accums less than an inch.

For DTW...The window of opportunity for snow showers will be between 06Z and 10Z. A forecast weakening of the forcing as the front moves across Se Mi suggests just a potential for a dusting of accumulation overnight

DTW THRESHOLD PROBABILITIES...

* Low in ceilings below 5000 feet this afternoon. Moderate tonight and low Sunday.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 10 PM this evening to 4 AM EST Monday for LHZ421-441.

Small Craft Advisory from 10 PM this evening to 4 PM EST Saturday for LHZ422.

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