textproduct: Detroit/Pontiac

KEY MESSAGES

- Bitter cold temperatures today. The coldest period will be this morning with wind chills ranging between 5 below zero and 15 degrees below zero.

- Lake effect snow banding possible along the eastern Thumb shoreline of Huron and Sanilac counties today. Snow accumulations of 2 to 4 inches are possible if snow banding does push inland off of Lake Huron.

- A warmup is forecasted for the middle of the week with temperatures near to slightly above normal Wednesday and some 8 to 10 degrees above normal Thursday.

- A strong storm system is forecasted to impact the Great Lakes region Thursday and into Friday. Much of the precipitation is expected to fall in the form of rain with the significant impact of the storm system coming from strong winds.

AVIATION

Winds just above the surface have come around to the northwest, which has allowed drier air and clearing to work into most of southeast Michigan. Another push of moisture/clouds from Lake Superior-Lake Michigan will spread in late this morning, along with scattered flurries/light snow showers. Mostly low VFR cigs expected this afternoon, but areas of high MVFR in snow showers. Increased mixing depths will support northwest wind gusts around 25 knots mid day, quickly diminishing in the early evening. Winds will back west- southwest this evening/tonight, but uncertainty with how well the southern Lake Michigan clouds/flurries will spread east and impact the taf sites overnight.

For DTW...Cigs under 5000 feet to redevelop late this morning and afternoon, with occasional flurries likely returning as well.

DTW THRESHOLD PROBABILITIES...

* Low for cigs aob 5000 feet, except medium toward noon and this afternoon.

* High for precip type being snow.

PREV DISCUSSION

Issued at 323 AM EST Sun Dec 14 2025

DISCUSSION...

A polar vortex amidst deeper planetary vorticity reservoir is currently centered in vicinity of northern Lake Huron this morning. The low height anomaly, distinguished by H5 heights of sub 510dam and 850mb temperatures of -24C will pivot directly across Southeast Michigan between 12-18Z. Spin down of vorticity will cause an excitement of the lakes with inductions of various mesolow features over the bigger lake basins of the Great Lakes. The main question has been whether any convergence banding will be shoved inland over the far eastern Thumb shoreline before becoming shore parallel for a time. Really a conditional, all-or-nothing type of forecast with differing hires solutions. The HRRR runs are the most bullish with some agreement from the ARW for pushing inland, while the 3km NAM and RGEM/HRDPS solutions suggest most of the lake effect snow will remain offshore. Local time-lagged ensemble output is mixed at site P58 with high probability >80% to measure but low probabilities <30% for a 0.5 inch snow. The same time-lagged ensemble systems convective method also calculates an approximate 30% chance for 1 inch of snow. NBM data is suggesting a miss with 60-70% probabilities for 0.1 inch, 0% probability of 2 inches, along the shoreline areas of Huron and Sanilac Counties. Lake effect parameters are very good for convective activity with water temperatures in the lower 40s providing for lake-850mb delta Ts of at least -20C and lake induced CAPE values reaching/exceeding 900 J/kg. Observed snow amounts will obviously be dependent on residence time/or the lack thereof of onshore snow banding later today. Any banding is expected to result in hourly snowfall rates of 1 per hour or possibly more. Out of respect for lake effect parameters, did increase snow amounts into the 2 to 4 inch range, again conditional to banding moving inland. A short-fused Winter Weather advisory may be needed.

Fast northwest flow will develop late tonight and Monday as broad ridging and supergeostrophic flow expands and reaches into Lower Michigan. Rising geopotential heights helps surface anticyclone build into Southeast Michigan with a weaker surface wind limiting wind chills into the single digits below zero Monday morning. Exit region to upper level speed max and attendant weak Pacific shortwave is expected to result in weak synoptic lift over the forecast area during the daytime Monday. Changing flow curvature is expected to result in a wave of warm advection aloft. Forecast soundings with vertical UVV profiles suggests saturation and lift will be very high up in the column at/above 8.0 kft agl with a considerable amount of dry air holding in the lowest 6.0 kft agl particularly south of I 69 corridor. Plan view of moisture on isentropic surfaces really supports the idea of a dry air feed into southeast Michigan from gusty southwesterlies. The offered guidance of 30 to 80% PoPs for the northern 2/3rds of the cwa appears reasonable. Snow amounts of a less than an inch in the Thumb also appears reasonable.

Relatively quiet weather for the middle of the week Tuesday and Wednesday as flow evolves more zonal and broad ridging influences the region. Not a whole lot to talk about right now, but many of the days are expected to breezy to windy. Near to slightly above normal temperatures are expected Wednesday with readings 5 to 10 degrees above normal Thursday.

Models have shown continuity in a deep midlevel trough pushing into the interior of the US Wednesday resulting in a strong baroclinic zone impacting the Great Lakes Thursday. Early indications are this will be an energetic wind producer with the potential for very strong winds with a bulk of the precipitation occuring in the warm sector. Uncertainty at this time is a result of differences in timing over Southeast Michigan.

MARINE...

The arctic front is now east of the area which has let the cold air begin to filter into the region through the day. The coldest of the arctic air will arrive overnight into Sunday morning with a secondary front turning winds a bit more to the northwest from west. Wind speeds will continue to be in the mid 20 knot range with gusts up to around 30 knots. The northwesterly flow will push the higher waves along the Lake Huron shoreline of the Thumb resulting in Small Craft Advisories the rest of the day through Sunday night. The cold airmass and elevated winds will also lead to potential snow squalls and freezing spray as well during this time. Monday will again feature elevated wind speeds as the next system tracking through southern Canada runs up against a high pressure system centered over much of the eastern conus. The tightening of the prefrontal gradient along with cold unstable air will lead to another period of wind gusts nearing gale force. Currently there is a large spread in the model guidance solutions as to what max gusts will be achievable but several hours of gales may be possible Monday afternoon.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Gale Watch from Monday morning through Monday afternoon for LHZ362- 363-421-422-441-462.

Small Craft Advisory until 4 AM EST Monday for LHZ421-441.

Small Craft Advisory until 4 AM EST Monday for LHZ442-443.

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