textproduct: Detroit/Pontiac

KEY MESSAGES

- Showers and thunderstorms increase coverage tonight, especially south of Detroit where rainfall totals range from 1.0 to 1.25 inch. Lesser amounts to the north.

- Showers linger Monday morning then dry weather follows in the afternoon and evening.

- Cooler than normal temperatures continue through at least the middle of next week.

DTW THRESHOLD PROBABILITIES

* High for ceiling at or below 5000 ft tonight and most of Monday.

* Low for thunderstorms tonight.

PREV DISCUSSION

Issued at 328 PM EDT Sun Jun 21 2026

DISCUSSION...

The hybrid baroclinic cyclone and mesoscale convective system is currently tracking out of Missouri and into Illinois early this afternoon. There has been a strong and very consistent model consensus that supports a split in the forcing with deep boundary rooted convection tracking to the southeast across far southern Indiana into portions of Kentucky, while seasonably strong 850mb and 700mb frontogenesis lifts northeastward towards the far western Lake Erie basin. Confidence is high the main synoptic scale lift and frontogenesis will favor this northern route as it is driven by strengthening and very rapidly organizing right entrance region jet dynamics. The low confidence portion for tonight remains how high up or what level the frontogenesis will activate. The current NAM nest suggests the center line of the 850mb fgen axis will set up to the south of the Michigan Ohio stateline, whereas the 700mb fgen axis tracks near Lenawee and Monroe counties while eclipsing Wayne County. Consensus of models suggests QPF amounts of 1.00 to 1.33 of inch will be likely with some peak amounts of 2.00 inch in isolated locations mainly across south central to southwest Lower Michigan. Was really agonizing over the decision to issue a Flood Watch, however a number of factors argue against it. The factors include: dry antecedent soil conditions, not expecting to reach 6 hour qpf amounts exceeding Flash Flood Guidance of 2.25 inches, QPF axis forecasted south of Metro Detroit, narrow QPF axis at a county wide or less, and no connection to true surface based instability reservoir.

Lead deformation/warm advection light rainfall chances begin after 22z across the Southern cwa, then increasing significantly after 01- 2z this evening. Early activity looks to have a more stratiform look based on hires depictions. Subset of model guidance points to a wave of low pressure causing a tighter cyclonic circulation to lift northeastward at Monroe County between 8-12z. It is with this compact convergence forcing that will bring the highest rainfall rates especially if there is more localized deformation response along the northern flank. Survey of model data suggests a top end of rainfall rates could be up to 0.50" per hour. Breadth of upper level jet forcing is expected to allow precipitation to expand over much of the area through the M 46 corridor.

Last of shearing deformation is expected to push east of Southeast Michigan by/after 18Z Monday. Guidance continues to suggest some brief potential for a light shower over eastern sections of the forecast area between 20-23z. Difficult to include a PoP later in the day with only a brief opportunity to achieve some reasonable convective depth with strong subsidence down to 7.0 kft agl. Spotty at best. Winds should be come well mixed in the dry advection, holding northeasterly to northerly at 15 to 25 mph into the early evening. Winds are then expected to lie down quickly after 00-01z. Surface ridge axis will build across Southeast Michigan Tuesday through midday Wednesday. Highs are expected to be in the upper 70s (2 to 5 degrees below normal) with modest surface dewpoints in the middle 50s.

Longwave trough and upper level jet axis settles into the central Great Lakes by late Wednesday. Models are suggesting a very broad cyclonic circulation which limits predictability because of timing in internal absolute vorticity maxima. At this vantage point, interesting to look at the EPS dataset which has mean values relatively close to the 75th percentile. Potential exists for a mainly dry stretch of weather next weekend near normal summerlike weather.

MARINE...

A compact low pressure system will travel east across the Ohio Valley tonight into tomorrow morning. This will elevate east to southeast flow across Lake Erie, bringing wind gust potential around 25 knots along with increasing wave heights. A Small Craft Advisory remains in place. Some isolated wind gusts 20 to 25 knots will be possible across Lake St. Clair overnight, with lower magnitude wind speeds across Lake Huron and the Saginaw Bay. This system will also bring widespread rain, heavy at times, across the southern Great Lakes. Wind direction backs north to northwest in the wake of the low through the early week period as high pressure builds in. Lighter winds are expected Tuesday and Wednesday.

HYDROLOGY...

Compact low pressure system will bring widespread rain to Southeast Michigan this evening and tonight. Total rainfall amounts of 1.00 to 1.25 inch appear likely for far southern sections of cwa with the potential for isolated amounts of up to 2.00 inches. Peak of the rainfall is expected between 3am to 8am. With no expectation for rainfall to exceed Flash Flood guidance, flooding impacts are expected to be limited to ponding of water on roadways and flooding of poor drainage areas.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...Small Craft Advisory from 4 AM to 5 PM EDT Monday for LEZ444.