textproduct: Detroit/Pontiac

KEY MESSAGES

- Widespread showers and some embedded thunderstorms are expected today.

- Chance for isolated strong to severe thunderstorm development this afternoon, favored along of south of I-94.

- Below normal temperatures Sunday through early next week.

DTW THRESHOLD PROBABILITIES

* High for ceiling at or below 5000 ft through this afternoon. Low tonight.

* Moderate for thunderstorms Saturday between 19z and 22z.

PREV DISCUSSION

Issued at 348 AM EDT Sat Apr 4 2026

DISCUSSION...

Occluded low pressure system now over northern Illinois and southern Wisconsin will continue to progress across northern lower Michigan this afternoon before departing into eastern Ontario and Quebec by late tonight. Progression of the low has resulted in numerous rain showers with some embedded thunderstorms across SE MI with shallow isentropic ascent along an advancing warm front. Isolated thunderstorms with heavy downpours remain possible through the morning hours, capitalizing on modest MUCAPE, but activity remains elevated noting the sharp inversion in the low levels with the 00Z RAOB. The 40+ knots llj on the southern flank of the low will result in extremely efficient moisture transport with pw values around 1.40 inches, which if verified would fall outside record values for early April per local sounding climatology. Moisture convergence with additional forcing ahead and along of a cold front will bring widespread rain and embedded thunderstorms through the afternoon and evening. A lull in activity will be likely across the Metro region and down into the MI/OH border later this morning, with prolonged rain chances setting up through the Tri-Cities, where the low and occluded front lies. This will coincide with the higher rainfall totals, as described in the hydrology section.

Latest 12Z data highlights a small window for some isolated strong to severe storms from roughly 18Z (2PM) to 22Z (6PM), favored along or south of I-94, where surface based cape briefly wedges in ahead of the cold front. HREF mean CAPE values range from around 800 J/kg down to the MI/OH border and upwards to 300 J/kg across the Metro region. Hodographs are relative straight from 0-3km owing to the unidirectional winds. Any type of development just ahead or along the cold front could have some better structure with some bowing that would be capable of producing damaging wind gusts with localized gust potential to around 60 mph. ML-output highlights a slightly elevated chance for tornado probabilities within the same area -- 0-3 km shear vector orientation is poor relative to the projected storm motion and 0-1km hodographs are not conducive to tornadogenesis. However, cannot rule out some highly localized streamwise vorticity driven by backed surface winds along the marine layer interface. Any overachievement of instability could expand the footprint for strong to severe potential into the north Metro region through Port Huron as highlighted in the latest SWODY1, but confidence in this expanded footprint is low.

The strong cold front moves through by the late evening, ending all rain chances while advecting in much cooler air. Lows drop into the 30s Sunday morning, which paves the way for below normal temperatures to last through the early week period. The next likely chance for some wintry precipitation then enters on Monday as a series of shortwaves arrive across the Great Lakes. Morning temperatures in the 30s bring the chance for melting snow to a rain/snow mix. Temperatures warm up into the 40s by the afternoon bringing increasing chances for rain, but steep lapse rates and lower freezing levels could bring some graupel with any convective based showers. A strong high pressure builds in Tuesday which effectively ends any precipitation chances. Clearing skies does bring what will likely be the coldest temperatures of the week, with lows in the 20s and highs holding in the 30s to low 40s Tuesday.

MARINE...

Easterly wind increases this morning ahead of a deepening low pressure system tracking in from the mid-Mississippi Valley. 20 to 25 kt winds with gusts to 30 kt are forecast today, with the highest wind magnitude across northern Lake Huron where fetch is maximized. Brief gusts to 35 kt gales will be possible at times in this area mainly between 8am and 2pm, but confidence is too low for a Gale Warning. Showers and thunderstorms overspread the area today, some of which may be strong to severe in the south. As the center of the low reaches the Straits this evening, wind direction veers around to southwest and remains gusty to around 20 to 25 kt. Strong cold advection follows this system on Sunday with gusts of 25 to 30 kt likely through the day. A Gale Watch was considered for northern Lake Huron on Sunday for 35 kt gales, but confidence remains below criteria at this time. Small Craft Advisories have been issued for the Lake Huron nearshore waters and additional advisories are possible for Lake St. Clair and western Lake Erie for Sunday. The gradient relaxes Monday causing wind magnitude to weaken, then a series of clipper systems bring cooler air and chances for snow showers Monday and Tuesday.

HYDROLOGY...

Several rounds of scattered to widespread rain with embedded isolated thunderstorms continues through the morning hours. A lull in precipitation will be likely across southern Michigan, before a cold front then brings a line of widespread showers and embedded thunderstorms this afternoon and evening. The Tri-Cities and northern Thumb will experience longer residence time for precipitation today given the track of the low pressure system. This brings increasing probabilities for local totals to achieve or exceed 1", with the current forecast highlighting possibly totals between 1 to 1.5" across the Tri-Cities and northern Thumb.

For locations south, basin averages range between a half-inch to three-quarter inches. However, any thunderstorm activity will be capable of producing localized total nearing or exceeding 1". Several river flood warnings are in effect across the Saginaw river. Localized flooding in low-lying or flood prone areas remain possible with any thunderstorm activity.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory until 10 PM EDT Sunday for LHZ421-441.

Small Craft Advisory from 4 PM this afternoon to 10 PM EDT Sunday for LHZ422.

Small Craft Advisory from 10 AM this morning to 10 PM EDT Sunday for LHZ442-443.

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