Area Forecast Discussion

KEY MESSAGES

- Scattered rain, graupel, and/or snow showers for the rest of this afternoon and evening with gusts to 40 mph and isolated lightning.

- A Freeze Warning remains in effect tonight for most of Southeast Michigan as lows drop into the mid 20s.

- Temperatures warm back toward normal Tuesday, climbing well above normal through the rest of the workweek.

DISCUSSION

Cooling aloft has resulted in steepening lapse rates, and with weak elevated moisture advection, an uptick in diurnal surface-based instability of 100-200 J/kg. Cyclonic flow will persist overhead and dynamically enhance UVVs as free convection emerges through the bulk of the troposphere, until the boundary-layer quickly shrinks with the loss of daytime heating. Showers should predominantly remain cellular for the rest of today featuring a variety of possible precipitation types: rain, melting snowflakes, and/or graupel. Surface dewpoints and relatively dry air beneath the cloud-bearing layer limit the overall intensity of precipitation and QPF, but additional isolated lightning strikes are likely. Gusty winds are still the main concern for the rest of today given the depth/dryness of the boundary-layer and enhanced evaporative cooling potential for rain and meltwater. With non-convective gusts of 25-30 mph, precip- loaded updrafts could easily produce gusts in excess of 40 mph.

Abnormally chilly tonight in the wake of a cold front extending well beyond its parent surface low, located near Hudson Bay. In addition to renewed cold advection, the frontal passage provides a northerly wind shift and decreasing speeds as high pressure builds in aggressively from the Upper Midwest. High confidence in overnight lows dropping into the 20s as 850 mb temperatures are likely to plunge around minus 10C by sunrise Monday. A Freeze Warning remains in effect given the heightened sensitivity of early season vegetation and minimal uncertainty in temperature trends.

Geopotential heights increase Monday morning as western CONUS longwave ridging broadens eastward and a shorter wavelength ridge axis extends from the Upper Midwest to James Bay. Subsequent thermal moderation will be slow to gain traction, so temperatures will be capped below normal again on Monday, only rising into the 40s. Surface high pressure of 1030 mb crosses southern Lower Michigan Monday afternoon maintaining dry conditions. The ridge exits into the eastern Great Lakes Monday evening which backs gradient winds southerly amidst ensuing return flow. A baroclinic zone develops upstream and will be the focus of shower potential Tuesday night, after the corresponding front gets released by a northern stream wave. Models continue to advertise higher productivity further south along the frontal slope where ThetaE convergence and instability is stronger. Outgoing forecast continues to highlight low chance PoPs/thunder south of I-94.

Longwave ridge amplification gets underway across central CONUS midweek which leads to rising temperatures, and eventually dewpoints, by the end of the workweek. Temperatures should maximize in the 70s with dewpoints in the 50s Thursday and Friday. Mainly dry conditions for Thursday as mid-level dry air and 7 kft capping inversion should limit convective chances. A cold front approaches on Friday with showers and potentially some storms.

MARINE

Gusty northwest wind accompanies a surge of colder air across the Great Lakes today. Gusts of 25 to 30 kt this afternoon and evening will decrease toward 20 kt overnight, and scattered showers will continue to dot the region. Small Craft Advisories remain in effect through this evening for western Lake Erie and Lake St. Clair, and into late Monday morning for the Lake Huron nearshore waters where wave heights will be slower to subside. High pressure builds into the Great Lakes on Monday promoting a period of less active weather with lighter wind. Gusty south wind then develops Monday night into Tuesday ahead of the next cold front tracking across the upper Midwest. The front settles across the region late Tuesday, bringing a chance for showers and thunderstorms mainly in the south. Weaker wind follows on Wednesday as the pressure gradient relaxes again.

PREV DISCUSSION

Issued at 126 PM EDT Sun Apr 19 2026

AVIATION...

High based, widely scattered showers have developed across all of southeast Michigan this afternoon. Beneath these high based showers and ceilings, steep low-level lapse rates have allowed for robust mixing to develop and continue to favor west to northwest winds with gusts of 25-30 knots. Throughout the afternoon and evening hours, west winds will gradually become northwesterly as a weak cold front drops south across the area.

Wind gusts in excess of 30 knots are possible, especially with more robust shower activity. Given the thermal profiles, more robust showers may end up a mix of graupel/rain and/or wet snowflakes. While we still cannot rule out a rumble of thunder, the best chance for a thunderstorm this afternoon appears to be in the vicinity of KDET and areas to the northeast where surface convergence along the surface front will be maximized.

Tonight, clearing skies are expected with light northwest winds as high pressure moves into the region. Northwest flow continues into Monday, then winds gradually back westerly and southerly as high pressure continues to move east of the region late Monday.

DTW THRESHOLD PROBABILITIES...

* Low to medium for ceilings at or below 5000 feet through the evening.

* Very low for a rumble of thunder this afternoon until 23z.

DTX WATCHES / WARNINGS / ADVISORIES

MI...Freeze Warning from 11 PM this evening to 11 AM EDT Monday for MIZ053-060>063-068>070-075-076-082-083.

Lake Huron...Small Craft Advisory until 10 AM EDT Monday for LHZ421-441>443.

Small Craft Advisory until midnight EDT tonight for LHZ422.

Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT this evening for LEZ444.