textproduct: Detroit/Pontiac

KEY MESSAGES

- Rain showers move across the area late tonight through Friday morning, with perhaps a rumble of thunder.

- Becoming drier and breezier through rest of the day on Friday.

- Turning much colder over the weekend with a chance for accumulating snow late Saturday night through Sunday.

- Large differences in snowfall are possible between the northern and southern areas of Southeast Michigan, with periods of initial rain and melting snow affecting snow accumulations.

- High temperatures drop into the 30s by Monday with scattered lake effect snow showers at times through Tuesday.

AVIATION

Upstream radar has filled in nicely late this evening in response to moisture convergence in advance of a mid level short wave and associated surface front. This region of rain, even a few embedded thunderstorms, will move into Se Mi between 09Z and 12Z. The period of forced ascent will generally be brief as the back edge of the more widespread rain is expected to exit east of the terminals by 15- 16Z. Ceilings upstream are largely VFR. Additional low level moisture convergence working into Se Mi during the morning will increase the probabilities for MVFR flight categories. Although some IFR conditions remain possible, latest guidance is becoming more supportive of predominately MVFR conditions during the course of the morning, with lingering low level moisture into the afternoon suggestive of MVFR and low end VFR based ceilings. Surface wind are increasing upstream with the approaching front. This supports the idea that there will be enough shallow low level mixing to refrain from LLWS in the terminals despite 2k ft level winds increasing to 40-50 knots. Mixing depths and a relatively strong low level wind field will support gusty west-southwest winds during the afternoon.

For DTW/D21 Convection... There is a low chance for an embedded thunderstorm within the rain pattern Friday morning, mainly between 12Z and 16Z.

DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less friday morning and afternoon. Moderate Friday night.

* Low for thunderstorms Friday morning.

PREV DISCUSSION

Issued at 317 PM EST Thu Nov 6 2025

DISCUSSION...

Active stretch of weather begins tonight with showers and perhaps a rumble of thunder. Potential for rain and snow continues to rise Saturday night into Sunday morning with a possibility for meaningful accumulating snowfall.

Short wavelength ridge passes overhead this evening and early tonight while respective surface high pressure center quickly spins into the Mid-Atlantic. By 03Z, upstream height falls begin to merge over the Upper Midwest as surface low pressure consolidates. This sets up a confluent southerly warm advection zone into Lower Michigan. Pressure progs indicate a period of very tightly packed isobars within the 06-12Z window (early Friday) indicative of prevailing winds in excess of 20 mph at times. A slight decrease in temperatures should occur for a few hours after sunset, then readings level-off (or climb by a degree or two) in the mid 40s through the rest of the overnight period. The aforementioned surface low is expected to track across The UP, dragging an initial cold front into Southeast Michigan.

An existing line of showers should be present along the frontal slope, coincident with aggressive ThetaE advection. Forecast soundings show strong static stability (and dryness) within the lowest 4 kft, but a shallow layer of steeper lapse rates exists near 10 kft. A few solutions indicate a bit of elevated CAPE (less than 40 J/kg), so a rumble of thunder cannot be ruled out within the most productive updrafts. Duration of rainfall should be rather brief (less than 4 hours), given column wind speeds of +40 knots above 2 kft. This lead cold front will not produce much of a thermodynamic change as 850 mb temperatures settle into the 4-6C range until the evening hours. This allows for 2m temperatures to climb into the upper 50s, and likely a few sites near 60F, especially if afternoon clouds clear ahead of schedule, before the secondary cold front drops through. Breezy/gusty for most of the day given the momentum fields, but gusts should be a bit more robust and frequent through the latter part of the day. A more pronounced wind shift (SW to W) corresponds to the second front during the late afternoon and early evening hours. This ushers in a colder airmass Friday night into Saturday as 850 mb temperatures drop below 0C. Lake effect activation promotes some showers off Lake Michigan overnight given cyclonic flow and favorable fetch. Coverage should remain very sparse, but melting flakes are possible.

Quite a bit cooler Saturday within the thermal gradient of the Canadian airmass with below normal highs (40s), albeit with a 10F spread from north to south. Isentropic perspective illustrates a component of mid-level downglide for most of the forecast area, so no precipitation concerns to speak of.

The amplified pattern becomes more consequential for Southeast Michigan Saturday night into Sunday, characterized by several key wave interactions. A mature tropospheric low over James Bay, an embedded shortwave trough aloft working around the back edge of the upper low, and another speed max riding the progressive southern stream jet. Models suggest the James Bay low undergoes rapid stretching as the waves constructively phase over the Midwest Saturday evening. The uncharacteristically long wavelength from the Texas/Mexico border to northern Quebec per 500 mb geopotential heights yields a large area of ascent, and favorable dynamics for low pressure to lift through the Ohio Valley. Spatial details regarding the most likely track remain in flux as the associated precipitation is still over 72 hours away, but this leaves several common Fall scenarios in-play. It is probable that some locations receive more rain than snow, and vice versa, especially at the start of the event when potential for a warm air intrusion is higher (ESE flow).

As Saturday night turns into Sunday morning, winds back northeasterly as the surface low ejects into Lake Erie or the southern Ontario peninsula. Most of the precipitation should fall between 06Z and 12Z with lighter activity through the rest of the day. Precipitation type and nocturnal cooling are high sources of uncertainty which are tied to system track sensitivities. A signal exists for more rain or rain/melting snow mix on the front-end as air temperatures will be slow to drop below freezing, let alone surface temperatures after being moistened by rainfall or melting snow. Based on thermodynamic diagnostics, sufficiently cold air for snow accumulations is more likely to reside over the northern half or northern third of the CWA, and are thus favored for higher totals compared to the downstate region. However, should FGEN activate amidst a more southerly trajectory, a broader area of colder air would promote a longer duration of snow and higher totals further south. At this time, snowfall totals are highly uncertain for any given location given the lack of model/ensemble consensus in resolving the timing of the phase transitions as has been outlined. The envelope of outcomes is still quite large.

Chilly Monday, and to a lesser degree Tuesday, with highs in the 30s. Periods of snow showers are possible as a tropospheric fold/PV anomaly drops through the Great Lakes spurring a lake moisture feed and tendency for synoptic-scale ascent. High potential for a changeover to rain or rain/snow mix on Tuesday.

MARINE...

Low pressure over the upper Midwest deepens as it tracks into the northern Great Lakes tonight, its center reaching the vicinity of the Soo Locks mid Friday morning. Southerly flow ramps up overnight in advance of this low and ushers in a milder air mass. This promotes a degree of low-level stability that will hold the higher magnitude wind core aloft, but gusty surface level winds are forecast to peak in the 25 to 30 kt range early Friday morning. Guidance has remained relatively steady in offering a 30 to 40% probability for a <3 hour period of 35 kt gales across portion of central Lake Huron between 1 AM and 7 AM. No plans for a Gale Warning at this time due to the expected brevity of occurrence. A band of rain will translate across the central Great Lakes in advance of the cold front set to move through during the late afternoon and evening. Post-frontal northwest wind is forecast to peak around 20 to 25 kt Friday night, though some gusts towards 30 kt will be possible over Lake Huron along the frontal passage.

The next low pressure system will track through the southern Great Lakes Saturday night into Sunday. There remains a considerable amount of model spread regarding system track, but this system will pull a much colder air mass across the region for the early week. Gusty northerly winds and snow will be likely during the daylight period Sunday. Most solutions currently hold gusts below gale strength, but will continue to monitor southern Lake Huron for headline considerations.

DTX WATCHES/WARNINGS/ADVISORIES

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

Small Craft Advisory until 4 AM EST Saturday for LHZ422-443.

Lake St Clair...Small Craft Advisory until 4 PM EST Friday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EST Friday for LEZ444.