textproduct: Detroit/Pontiac

KEY MESSAGES

- Periods of showers and thunderstorms will affect the area tonight through Tuesday evening. Isolated severe thunderstorms are possible tonight. Scattered severe thunderstorms are possible Tuesday with damaging wind being the primary but also including potential for large hail and tornadoes.

- A strong cold front fuels storms but also a chance for excessive rainfall. There is a Marginal Risk of excessive rainfall mainly along and south of M-46 Tuesday afternoon and evening.

- After the front Tuesday night, temperatures drop back to normal or slightly below normal for Wednesday through late week.

- Another system will bring rain and a chance of thunderstorms Wednesday night into Thursday.

AVIATION

A notable increase in low level moisture under sustained southwest flow will maintain a weakly unstable environment overnight. This will sustain a lower probability for some form of convective shower and thunderstorm activity to develop near a frontal zone draped across central lower Mi and/or through downstream propgation of ongoing activity over northern Illinois. Confidence in occurance at any one location remains low through Tuesday morning and precludes a defined mention outside of MBS early this morning. Otherwise, VFR under intevals of thicker mid-high based cloud into the morning period. Highest likelihood for thunderstorm development will focus across the Tuesday afternoon and evening periods, as a southward sagging cold front engages increasingly unstable conditions. Outgoing forcast outlines the most likely window, with further refinement of specific timing expected as confidence improves with time. For DTW...Very low probability for a shower or thunderstorm late tonight and Tuesday morning. The highest probability exists Tuesday afternoon and evening, with one or more rounds of convection possible within this window.

DTW THRESHOLD PROBABILITIES...

* Low for cigs aob 5000 ft through Tuesday morning, then medium Tuesday afternoon and evening. * Low for thunderstorms Tuesday.

PREV DISCUSSION

Issued at 306 PM EDT Mon Mar 30 2026

DISCUSSION...

Afternoon temperatures across Se Mi have rising into the low 70s within ongoing low level warm air advection. A surface cold front, now over the northern Great Lakes, is forecast to sink south into the northern Saginaw Valley/thumb region tonight, forcing the post frontal lake modified cold air into the far northern sections of the forecast area. Strengthening southwest flow in the low to mid levels will in turn advect deep layer moisture from the lower-mid MS Valley this afternoon across the southern lakes region tonight. Meanwhile, very steep mid level lapse rates will result in decent elevated instability overnight (0-3km MU CAPE possibly over 1500 J/kg). The initial mid level theta e surge this evening will support a chance of convection. Additional moisture advection overnight within the time period of steeper lapse will lead to increased convective chances, especially across the northern half of the forecast area closer to lower tropospheric frontal forcing. The degree of elevated instability and strong mid level wind fields will support isolated strong to severe convection. Limited boundary layer stability suggest strong winds in addition to hail will be the primary severe weather concerns. Ideal hodograph structure along the cold front across the Saginaw Valley/thumb raises some concerns for isolated supercells. This potential looks to be very limited based on weak surface instability.

There is the potential for a couple of rounds of convection on Tuesday as resident deep layer moisture and an axis of steep mid level lapse rates reside overhead. Low level frontogenetical forcing will also be present as the aforementioned cold front gradually sinks south during the day. Hi res models present an array of timing of the convection across the area, much of which will be dependent upon timing and coverage of nocturnal convection and associated convective short wave impulses. Deep layer shear profiles will remain supportive of strong to severe convection, predicated upon the availability of surface based convection. Both linear and supercellular storm structure will be favored based on forecast hodographs. The passage of the cold front will be marked by a drastic cool down given the degree of shallow post frontal cold air.

Low to mid level anticyclonic flow will envelop the northern Great Lakes Wednesday, ensuring dry conditions across the northern half of the forecast area. The cold front is forecast to stall across the Ohio Valley, with the elevated portion of the front remaining active through the day Wednesday, warranting chance type pops across the south. A progressive mid level wave forecast to lift from the southern high plains Wed night into the western Great Lakes Thurs night will drive the front back north as a warm front Wed night/Thursday morning. The thermal profile within the shallow cold air across the Tri Cities and northern thumb will support mixed precip in these locals Wed night. Recent probabilistic guidance has reasonably high probabilities for trace to a tenth inch of ice north of M 46. By Thursday most of the forecast area is forecast to be in the warm sector, suggesting a chance for thunderstorms. Medium range guidance then indicates the surface low and associated cold front tracking across Lower Mi Thurs night into Friday.

MARINE...

Broad southwest flow will veer to the east for most of Lake Huron by this evening as the next low pressure system and its warm front gain influence locally. The shift in flow will also be accompanied by an expansion of showers and elevated thunderstorms overnight into Tuesday morning, where hail will be the primary threats. The surface low tracks across northern Michigan Tuesday afternoon, drawing a cold front across lower Michigan and adjacent marine waters in its wake. A line of strong to severe thunderstorms will be possible along the frontal passage Tuesday evening, in which localized gusts in excess of 35 knots will be possible. Elevated winds and/or waves will be driven mainly by thunderstorm activity, as otherwise stable conditions prevent gusts from mixing to the surface. A cooler post- frontal airmass then moves in mid-week as flow shifts to the northwest Tuesday night with the fropa. High pressure then drifts across Ontario Wednesday, causing winds to veer around the southern edge of the high before the next system lifts into the area Thursday.

HYDROLOGY...

Periods of showers and thunderstorms will affect the area tonight through late Tuesday. Locally heavy rainfall is likely with the strongest storms. Model ensemble means suggest high probabilities for 12 to 24 hour total rainfall of 1/2 inch to an inch. There is however low probabilities for total rainfall of 2 to 4 inches within regions that see more persistent thunderstorms. Localized flooding is possible, especially in more urbanized areas. A slow moving frontal boundary will linger across the metro Detroit and Ann Arbor areas Tuesday night into Wednesday, supporting additional chances for light rain. This front is forecast to lift back north Wed night, with a slow moving cold front then forecast to approach Thurs into Fri. These systems will produce additional rainfall, with current projections suggesting additional rainfall remaining an inch or less.

DTX WATCHES/WARNINGS/ADVISORIES

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