textproduct: Detroit/Pontiac

KEY MESSAGES

- Light rain along and north of I-69 this afternoon continues increasing over SE MI this evening. - After a break during the morning, showers increase again as a strong cold front sweeps north to south over the region Thursday afternoon.

- The front also brings in a much colder air mass on gusty north wind.

- The inbound cold air activates lake effect rain/snow showers Thursday night through Saturday. Minor wet snow accumulations are likely across the Thumb, mainly near Saginaw Bay and the Port Huron vicinity.

DISCUSSION

The cold air surge is on schedule for late week as a reminder that winter is on our doorstep, even during a strong El Nino year. The temperature change follows a complex system of low pressure tracking through the Great Lakes and Ohio valley today and tonight. It brings several rounds of rain showers to the region until depth of below freezing air becomes sufficient for snow Thursday night. Lake effect contributions give the Thumb area the best chance for some accumulation by Friday morning.

Bands of rain showers continue increasing over SE Mi this afternoon and evening as the Ohio valley mid/upper level wave phases with the northern Ontario trough. These systems are well-defined in afternoon observations, both in surface analysis and satellite imagery. Model analysis fields indicate the leading low level frontal zone stretched out from the Ohio valley up into northern IN/OH, and this is where ongoing northern IL convection remains focused. The combination of the mesoscale mid level circulation near southern Lake Mi and the northern Ontario trough are building a mature 700 mb moisture axis that feeds the shower pattern up to the northern Great Lakes surface low and intermediate cold front entering northern Lower Mi. This forecast cycle leans toward borderline categorical coverage of light rain along and north of I-69 this evening and then decreasing after midnight. The northern Ontario mid/upper level trough then sharpens considerably overhead during Thursday, and this powers the primary cold front through Lower Mi during the afternoon. Coverage of rain showers becomes numerous to widespread again but is confined relatively close to the surface trough as it moves north to south and exits into Ohio by Thursday evening.

Today's forecast cycle has slightly higher QPF and a slightly larger footprint of snow accumulation in favored areas of the Thumb Thursday night, mainly near Saginaw Bay and the Port Huron vicinity. This is where wind speed and direction favor longer duration of more intense lake effect bands, but still subject to all of the limiting factors mentioned in our early morning forecast discussion. Lake Huron water in the 50s maintains an all rain boundary layer over the lake and at least a rain/snow mix near the shoreline, then cooling to all snow farther inland. The lake aggregate air mass that covers the rest of Lower Mi is cold enough for snow, although REFS mean surface T and Td are still hovering around the mid 30s by sunrise Friday. These thermal characteristics continue to support holding snow ratio in the single digits in borderline rain/snow mix for the event while mainly adopting the areal QPF adjustments from the 11/12Z model cycle. Considerations to also monitor on the side of accumulation overachievement are tied to model soundings that support an impressive lake effect profile having convective depth around 10 kft with large CAPE density into the DGZ. A resulting colder/high rate dominated thermal profile and surface temperature could be a contributing factor in the much higher snow accumulation shown in REFS members and ensemble means through Friday morning.

Lobes of short wave energy round the west flank of the long wave trough Friday afternoon into the weekend. This keeps Lake Huron activated into the weekend while wind veers more offshore by Saturday. Extended range models indicate surface high pressure makes an aggressive move into Lower Mi for improving conditions by Sunday.

MARINE

The passage of low pressure across the Ohio Valley today will reinforce northeast to north flow across the Great Lakes starting tonight and lasting through the week. This will usher in much cooler air across the seasonal warmer waters of the Great Lakes, bringing unsettled weather and elevated winds and wave heights for the remainder of the week. The boost in near surface instability will see sustained winds and gusts quickly increasing tonight, producing gusts of 25 to 30 knots through much of tomorrow for most of the eastern Great Lakes. Localized higher gust potential through the Saginaw Bay will be possible tomorrow morning and early afternoon when a brief window for favorable northeast flow sets up. Isolated gust to gales will be possible within this corridor during this time, but confidence is low that we will see the required 3+ hour time window needed to trigger gale headlines.

Wind gusts then diminish slightly through Friday, but breezy conditions are still expected to persist across Lake Huron. Widespread to numerous lake effect rain showers are also likely under this setup with the best coverage expected across Lake Huron. An isolated waterspout remains possible with rain shower activity. High pressure to build in on Sunday, relaxing wind speeds and ending lake effect rain chances.

PREV DISCUSSION

Issued at 1242 PM EST Wed Nov 11 2026

AVIATION...

A pair of lows will impact the region through the forecast period resulting in MVFR conditions and periods of rain. One low is tracking just south of the state line while a second low will drop SE through the state this evening pulling a cold front along with it. Overall we'll see deteriorating conditions with lowering ceilings and periods of reduced visibilities within areas of light rain. A west to east band of rain is setting up across Mid MI which will impact MBS and maybe FNT this afternoon, it fills in southward across the rest of the terminals this evening for a few hours. Ceilings will lower through the night to MVFR with the front pulling lower stratus and showers through Thursday morning. Light winds this afternoon will become more northeasterly this afternoon as the southern low draws near, and then becomes gusty out of the north behind the cold front for Thursday with gusts of 20 to 25 knots.

DTW THRESHOLD PROBABILITIES...

* Medium for ceilings at or below 5,000 feet late this afternoon- evening. High tonight into Thursday morning.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None.

Lake Huron...Small Craft Advisory from 1 AM Thursday to 10 PM EST Friday for LHZ421-422-441.

Small Craft Advisory from 4 AM Thursday to 10 PM EST Friday for LHZ442-443.

Lake St Clair...Small Craft Advisory from 10 AM Thursday to 4 AM EST Friday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 10 AM Thursday to 4 AM EST Friday for LEZ444.