textproduct: Detroit/Pontiac

KEY MESSAGES

- Potential for a few showers to develop this afternoon.

- A cooler air mass settles over the area tonight through Monday night. Tonight will feature to coolest night, with overnight lows falling into the 40s.

- Unsettled weather returns Tuesday and lingers into late week. Tuesday will feature a warmer more humid day helping to set the stage for thundestorms chances as a slow moving front arrives.

DTW THRESHOLD PROBABILITIES

* None

PREV DISCUSSION

Issued at 333 PM EDT Sun Sep 13 2026

DISCUSSION...

A split structure to the baroclinic zone exists across the Great Lakes region with the surface dewpoint discontinuity/front well to the south of the midlevel frontal extension. Upper level jet streak will progress through the basal portion of the composite trough axis this afternoon bringing an increase in anticyclonic flow trajectories. So while Southeast Michigan will become increasingly on the cold side of the boundaries, the greatest dcva with the absolute vorticity maximum will occur in the 18-00z time window. Models continue to support modest 870-700mb fgen response 21-01z associated with the vorticity maximum primarily north of I 69. Thought about increasing PoPs into the likely range, but with lean 1000-700mb mean RH decided to stay with PoPs of around 30%.

Extensive stable surface high pressure will build directly through Southeast Michigan tonight and Monday. 850mb temperatures dropping +3C to +5C and a light wind environment will result in chilly 40s for Monday morning lows. There could be a few locations, Midland County, that could see upper 30s but given peak evapotranspiration of vegetation believe that temperatures will remain buoyed to some extent. Highs Monday afternoon, near 70, are expected to be some 3 to 5 degrees below normal.

Dynamic upper level low pressure is progged to eject out of the Rockies through the Northern Plains and into far western Ontario Monday night. Taste of Autumn with the strength of the pressure gradient bringing strong southerly flow and associated moisture transport to Southeast Michigan Tuesday. Current forecast suggests a noteworthy surge in surface dewpoints above 70 degrees with south winds of 15 to 30 mph. Questions remain on how progressive the band of precipitation will be or whether it will remain intact as there are some signals that upper level ridging could hold across Metro Detroit until late Tuesday. Low level jet becomes veered with trajectories due westerly so southern portions of the forecast area could very well be split by the best forcing. Ensemble guidance suggests its may take until Wednesday to get more meaningful precipitation chances into the area as shortwave energy continues to ring around the upper level ridging to the south. Many moving parts here but the interquartile range of 24hr QPF does increase to .25- 0.5 inch by the first half of the day Wednesday for Metro Detroit. Secondary increase in synoptic scale forcing appears set for late Wednesday and Tuesday as another upper level jetlet and right entrance region dynamics stripe across the area. Increase in ageostrophic circulation could result in stalling warm front and persistent upward vertical motion. From this vantage point the most likely timeframe for heavy rainfall potential may be Thursday morning.

MARINE...

Cooler air will continue to work in over the region this afternoon from the northwest, favoring an uptick in west to northwest winds. West winds increase to 25-30 knots this afternoon, gradually becoming northwest through the evening. Small craft advisories will continue for all nearshore waters through tonight into early Monday for a combination of wind gusts in excess of 25 knots and/or 3+ foot waves.

High pressure quickly builds into the region Monday, allowing northwest winds to relax in/around daybreak. Attention then turns to a robust surface low progged to track across the Canadian Prairies Monday into Tuesday, and eventually reaching the Hudson Bay region by Tuesday night/Wednesday. Surface wind fields respond to both the pressure falls north of the region and the increasing surface pressure gradient arriving late Monday through Tuesday. Will need to keep a close eye on the forecast for Monday night through Tuesday as south to southwest gales continue to look more likely. There remains some disagreement amongst the guidance regarding what the high-end potential of wind speeds look like. However, blended ensemble guidance show a strong signal for 35-40 kt gales peaking Tuesday morning over the open water of Lake Huron. There is enough confidence in gales to issue a Gale Watch for Tuesday. These strong south winds will also usher back in better fuel for thunderstorm activity and heavy rain.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement through Monday morning for MIZ049.

Lake Huron...Small Craft Advisory until 2 AM EDT Monday for LHZ422.

Gale Watch from late Monday night through Tuesday afternoon for LHZ362-363.

Small Craft Advisory until 8 AM EDT Monday for LHZ421.

Small Craft Advisory until 11 AM EDT Monday for LHZ441>443.

Lake St Clair...Small Craft Advisory until 2 AM EDT Monday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 2 AM EDT Monday for LEZ444.