textproduct: Detroit/Pontiac

KEY MESSAGES

- A period of wind gusts around 40 mph this evening.

- Showers and embedded thunderstorms this evening into early tomorrow morning.

- Much colder air arrives by the end of the work week and holds through the weekend.

DISCUSSION

The transition from a mild, ridge-dominated pattern to a deep, unseasonably cold regime remains the primary meteorological focus as a massive 500mb closed low descends from Central Canada to stall over the Great Lakes by the end of the work week. Immediate attention centers on a robust moisture surge tonight, fueled by a potent 45-60 kt Low-Level Jet (LLJ) ahead of a surface low tracking toward Lake Superior. This surge will push PWAT values above 1.25 inches as an 850-700mb theta-e ridge traverses Southeast Michigan around 06Z Tuesday. Despite this moisture, convective potential tonight will be hampered by the diurnal minimum and a lack of surface-based instability, likely resulting in a waning trend for showers and elevated thunderstorms as they move east. This is supported by latest HRRR and RRFS guidance, a trend further supported by convection in the Ohio Valley effectively cutting off the deeper Gulf moisture. Rainfall totals are forecast to average between 0.20 and 0.50 inches, though steepening mid-level lapse rates could support localized higher amounts in more persistent elevated cores. The seasonably strong low (993 MB) tracking through the Western Great Lakes and strong low level jet leads to some concern winds could reach/exceed 45 MPH, as convectively induced rise/fall pressure couplet approaches, but upstream trajectory suggests the core strongest winds remain west-northwest of southeast Michigan. Weakening of the line and arrival closer to sunset expected to keep gusts in check, but will continue to monitor.

Following a brief period of drier air behind a Tuesday morning cold front, attention shifts to a deepening surface low triggered by a southern-stream shortwave lifting through the Ohio Valley Tuesday night into Wednesday. While the bulk of this system's moisture will remain to our south, favorable forcing and a sharpening deformation zone should spread rain showers across the southern and eastern CWA through Wednesday afternoon. As this wave exits, the 12Z ECMWF and CMC show high confidence in the large-scale polar trough fully capturing the Great Lakes, ushering in a prolonged period of cold air advection with 850mb temperatures plunging into the mid to upper single digits below zero Celsius by Friday. This setup will foster steep lapse rates and significant lake-induced instability, resulting in significant cloud cover and "small core" isolated showers of rain, graupel, and wet snowflakes through Saturday. High temperatures will struggle to reach the lower 50s (10 to 15 degrees below early May normals). Frost/freeze potential during the night time/early morning hours for the end of the work week and weekend.

MARINE

High pressure influence breaks down today as a cluster of thunderstorms rolls through the Ohio Valley. Most of the convective activity associated with the mesoscale system will wane prior to reaching the southern waterways, but a few rumbles of thunder cannot be ruled out this evening. Meanwhile, a low pressure system will track into the northern Great Lakes later this evening, centered within a potent/expansive low-level wind field. Forecast soundings across Lake Huron remain stable to the lake surface, but with flow in excess of 40 knots within the lowest few hundred feet, opted for a Gale Warning for the northern two thirds of Lake Huron. The period of gales should be brief given the translation speed of the parent wave, but latest model trends continue to support minor increases in confidence for occasional gusts to gales. To further capitalize on the energetic winds, additional convection is expected ahead of the system's warm front which should surge all the way up to The Straits. Elevated storms emerge ahead of the surface boundary, and should augment the stability profiles. Small Craft Advisories remain in effect for all nearshore waters until Tuesday due to elevated winds/waves. Wind gusts could briefly approach gale-force for Saginaw Bay and maybe The Thumb. The system's cold front then crosses through the central Great lakes during the day on Tuesday, leading to calmer weather and a shift to northwest flow as high pressure builds in mid-week.

PREV DISCUSSION

Issued at 154 PM EDT Mon Apr 27 2026

AVIATION...

Low pressure tracks from southern Minnesota to Lake Superior tonight, sending a cold front across the airspace Tuesday morning. Strong low level jet (50-60 knots) ahead of the front reaches SE Michigan this evening-overnight, but will struggle to overcome the stable near-surface layer. Added low level wind shear to the TAFs as a result, although moistening of the boundary layer may mix gusty winds to the surface on a more localized basis. The jet draws moisture northward, bringing waves of shower activity into the airspace overnight. There is a low chance for isolated/embedded thunderstorms within this shower activity, but will be limited by weak instability (under 500 J/kg). Southeast winds gradually veer south tonight before a more abrupt shift to the west occurs with the frontal passage Tuesday morning. The front also scours out low level moisture, with MVFR ceilings in the morning beginning to scatter out by early afternoon.

D21/DTW Convection...Several windows for upstream convection to approach the area, currently centered on 22z-02z and 03z-06z. Instability will be a limiting factor locally and convection is expected to exhibit a weakening trend with eastward progression. LLWS is expected tonight, although gusty winds may mix to the surface within any shower or thunderstorm activity.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms tonight between 22z-01z and 03z-06z.

* Moderate for ceilings aob 5000 feet after midnight, high Tuesday morning.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Gale Warning from 1 AM to 8 AM EDT Tuesday for LHZ361>363.

Small Craft Advisory until 10 PM EDT Tuesday for LHZ421-422.

Small Craft Advisory until 4 PM EDT Tuesday for LHZ441>443.

Lake St Clair...Small Craft Advisory from 8 PM this evening to 4 PM EDT Tuesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 8 PM this evening to 4 PM EDT Tuesday for LEZ444.