textproduct: Detroit/Pontiac

KEY MESSAGES

- Scatted showers with a few isolated thunderstorms overnight.

- Unseasonably warm Tuesday with highs above 80F.

- Showers possible Tuesday night into Wednesday.

- Turning more seasonable Thursday and Friday, then becoming chillier over the weekend.

DISCUSSION

Very warm today with a record high already broken at FNT, based on a 20Z obs of 85F, but even warmer readings exist further northwest as IKW, MBS, and HYX log readings of 88F, 86F, and 86F, respectively.

An active period of weather gets underway this week as the upper level jet approaches the Great Lakes and then fixates through the workweek. At the surface, a chain of surface low pressures is anchored to a stationary front extending from the High Plains to the Upper Midwest. A shortwave trough will eject from a deep upper low stuck over Nevada tonight to establish a primary surface wave that will reach Lower Michigan on Tuesday. Meanwhile, a 594 dam 500 mb ridge of high pressure situated over the Gulf Coast supports continued anticyclonic warm/moist advection into the region. Moisture metrics are already on the rise this afternoon with most ASOS/AWOS sites reporting 60+ dewpoints. This ensures a mild night with overnight lows in the mid (perhaps upper) 60s, or about 20F above climatological normals. Before the low makes any progress into northern Lower, isentropic upsloping produces an uptick in mid column saturation (700-500 mb) while drier air resides within an elevated warm layer (925-800 mb). Scattered overnight showers will partially fill in overnight, and remain elevated. Forecast soundings show some elevated instability, maximizing at around 200 J/kg, so some rumbles of thunder cannot be ruled out. No severe weather concerns given the lack of CAPE density for severe hail and near- surface stability to dampen the wind gust response.

CAMs show conditions drying out pretty quickly Tuesday morning given how quickly low and mid level moisture is stripped out, after flow veers WNW. The main forecast consideration will be temperature trends for the rest of the day with 925 mb temperatures starting out in the low 20s (Celsius). Skies should also clear out for the peak diurnal heating cycle, adding to the insolation potential. Models differ in timing the arrival of the primary cold front, but the more delayed the boundary is, the higher the possible max temperature will be. The latest NBM 5th percentile has 80s across most of Metro Detroit, so NWP confidence is high for another day with highs of 80F. The record high for DTW on October 13 is within reach at 83F in 1975. Seasonably mild Tuesday night behind the front, although still a 20+ degree nocturnal drop, even with thickening cloud cover.

The cold front looks to stall out near the Michigan/Ohio border Tuesday night and Wednesday as the jet axis approaches aloft. Numerous shortwave interactions promote a perturbed geopotential height field offering additional chances for precipitation. This will be augmented by the Gulf ridge which will still be in place, renewing theta-e advection. Limited CAPE, but non-zero leaves a chance for a rumble of thunder. Any shower activity that continues into the daylight hours will be brief as shortwave ridging builds in from the west, and flow flips NNE, dislodging the boundary. This also allows a more seasonable airmass to filter in from Ontario. Cold advection persists into Thursday, before the next wave of low pressure lifts into southern Lower Thursday evening or during the overnight hours. This brings another round of rain and a cold front. Cooler and drier conditions develop Friday, lasting through the weekend.

MARINE

Low pressure will travel from the Plains into northern lower Michigan tonight through tomorrow morning. This will quickly strengthen the pressure gradient ahead of the arrival of this system, increasing the magnitude of southwest flow across southern Lake Huron, Lake St. Clair, and Lake Erie. More tempered northerly flow will be found across northern Lake Huron through the morning. As low pressure progresses east into New England, wind direction will back more westerly through the afternoon, which will bring a window for some breezy conditions across the southern Great Lakes. Wind gusts around 20 to 25 knots will be possible, with wind speeds quickly diminishing through the evening as the pressure gradient weakens. Rain showers with some isolated thunderstorms will be likely through tomorrow.

A cold front will then push through the Great Lakes Wednesday, stalling across southern Michigan by the afternoon. The favorable northwest fetch will produce wind gusts 20 to 30 knots across northern Lake Huron. High pressure to then build in through Thursday which will bring a period of light winds for the day. Confidence is increasing for a strong cold front to pass Friday into Saturday. Instability will increase over the lakes in the wake of the front given the advent of cold air over the warmer lake waters. Coupled with longer duration northwest flow, a longer duration gale event is looking increasingly likely to end the week.

CLIMATE

Record high max temperatures for October 13th:

Detroit: 83 Degrees (Set in 1975) Flint: 83 Degrees (Set in 1975) Saginaw: 86 Degrees (Set in 1930)

PREV DISCUSSION

Issued at 205 PM EDT Mon Oct 12 2026

AVIATION...

Longwave ridging will expand eastward today and tonight continuing a strong warm advection episode across the Great Lakes. Warming in the lowest 6.0 kft agl maintains high stability and VFR conditions through the early to mid evening hours. Synoptic scale ascent combined with a jet exit region will then support a wave of low pressure and fast moving low through Lake Superior basin tonight and Tuesday. Introduction of thetae/moisture at/above 7.0 kft agl will create conditionally unstable conditions aloft tonight. Differential cyclonic vorticity advection looks to bring a period of showers or elevated thunder to MBS between 04-07z with a lower probability at the Metro Detroit taf sites. Post frontal subsidence is forecasted to result in a capping inversion for the daytime Tuesday. Lower mixing depths will help to tame winds during the daytime to the 15 to 30 knot range.

D21/DTW Convection... Very low chance for a thunderstorm late tonight near DTW or in the D21 airspace.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms in the 05-08z time window tonight.

DTX WATCHES/WARNINGS/ADVISORIES

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