textproduct: Detroit/Pontiac

KEY MESSAGES

- Showers and thunderstorms increase coverage this afternoon and evening with the strongest storms capable of producing isolated wind gusts up to 60 mph and localized heavy downpours.

- Drier this weekend with seasonable temps.

- Showers and thunderstorms return Monday night into Tuesday.

UPDATE

A pocket of showers is holding on across the Detroit metro area within an axis of elevated instability that has been advancing SW to NE across Lower Mi this morning. This activity continues eastward while weakening and as the low to mid level theta-e ridge builds into the region setting the stage for surface based convection this afternoon.

The morning SPC outlook expanded the Marginal Risk across the rest of SE Mi for the storms on schedule to increase coverage and intensity this afternoon. Late morning satellite imagery shows cirrus still thin enough to allow sufficient afternoon heating for instability increasing toward the higher end of guidance projections. The latest RAP runs indicate surface based CAPE reaching the 1500-2000 J/kg range while model soundings show a skinny CAPE density profile with high moisture content within an HREF mean PW axis reaching up to around 1.5 inches. The wind profile ends up being more of a limiting factor as 0-6 km bulk shear reaches up around 25 knots, enough for multicell clusters presenting a precip loaded downburst wind threat. A mostly uncapped thermal profile then allows early to mid afternoon coverage expansion forced by the inbound mid level short wave and ahead of the associated surface cold front. The pattern will be monitored for a few of the strongest storms reaching severe intensity, along with localized heavy rain, during the late afternoon and early evening peak and before the front sweeps activity eastward before midnight.

PREV DISCUSSION

Issued at 653 AM EDT Fri Apr 24 2026

AVIATION...

VFR conditions this morning as mid to high clouds are increasing down stream of a low pressure system and cold front moving across the Midwest. Models combined with the radar observations this morning point towards a low chance for scattered showers this morning, enough to keep mention out for now as activity should be isolated enough to leave mention out of the TAFs at this time. Cold front progression will bring likely showers with scattered thunderstorms this afternoon and evening focused mostly between 18 and 02Z. Following the front will be MVFR to IFR ceilings/vsbys as trapped low moisture supports low clouds and patchy fog across southeast Michigan tonight into tomorrow morning.

For DTW...Greatest thunderstorm potential across DTW currently will be between 19Z and 01Z a the line of strong to potentially severe thunderstorms move through. Damaging wind gusts and locally heavy downpours are the main threats.

DTW THRESHOLD PROBABILITIES...

* Moderate to high for thunderstorms this afternoon-evening.

PREV DISCUSSION... Issued at 325 AM EDT Fri Apr 24 2026

DISCUSSION...

Longwave ridging over the Great Lakes is beginning to break down this morning as a broad closed low centered over southern Saskatchewan sends a lobe of vorticity across the Midwest. A theta-e ridge is advecting in on low- to mid-level southwest flow and will set the stage for a couple opportunities for convection today. The first is focused between 8am and noon as the decaying LLJ works in to provide a 20 to 40% chance of showers. A rumble of thunder can't be ruled out for any more vigorous cells, but shallow convective depths will preclude a thunder mention in the forecast later this morning.

Today will be another unseasonably warm and humid day as we sit within the warm sector of a surface low that tracks across the Lower Peninsula this evening. High temps are forecast to reach some 15 to 20 degrees above normal, in the mid to upper 70s for much of the area. Dew points likewise rise to around 60, promoting modest afternoon/evening instability west of I-75. Southeast wind will dominate areas east of I-75 which keeps areas downwind of the lakes cooler and more stable; highs mainly in the 60s.

The second round of convection, driven by PVA working in atop the inbound cold front, spreads across the area 4pm to 10pm. This period carries much higher confidence in precip occurrence and coverage (70- 90%) given the frontal forcing, and thunder will be more probable given modest instability. SBCAPE progs have trended up slightly with the latest guidance (500 to 1000 J/kg), supportive of some strong to marginally severe storms. Weak bulk 0-6km wind shear (aob 20 kt) will be a limiting factor, but may be sufficient for some organization into multicell clusters along the front. SPC day 1 marginal outlook aligns with available hi-res ensemble and ML guidance which offers a low probability for wind gusts of 40 to 60 mph in the strongest storms. Greatest potential for this will be west of I-75 where the most instability and steepest low-level lapse rates near will develop. The humid environment with PWAT peaking near 1.25 inches and relatively slow storm motion will support heavy downpours and potential for localized minor flooding, particularly if any urban areas see repeated storms.

The cold front pushes through during the late evening and overnight which allows coverage of showers and storms to wane after 10pm. Marine layer augmented low-level moisture will get trapped beneath the developing frontal inversion, bringing potential for patchy fog and/or drizzle after midnight into Saturday morning. Cooler post- frontal north to northeast flow persists through the rest of the day, promoting mainly overcast skies and temps more characteristic of late April, peaking in the 50s and lower 60s. Shortwave ridging strengthens overhead into Sunday to maintain dry and seasonable weather as surface high pressure extends south from northern Ontario/Quebec.

Upper low remains nearly stationary over the Canadian Prairie over the weekend, eventually beginning to dislodge Monday into Tuesday. This process helps eject a shortwave from the Four Corners into the Great Lakes Monday night into Tuesday which serves as the next window for convection. Consensus of guidance tracks the ensuing surface low northeast across the Midwest and places SE MI within a narrow warm sector nearing occlusion Monday night. Strong PVA signal offers relatively high confidence in showers and thunderstorms during this period. Longwave troughing then looks to set up across the region which points to a period of cooler conditions through the rest of the week.

MARINE...

A warm front will continue to lift over Great Lakes region into the morning. A low pressure system over the upper Midwest will move into the northern Great Lakes through the day and into Saturday. This will bring chances for widespread showers and thunderstorms to the region during this time as the cold front pushes through. Ahead of the low on Friday, southeasterly winds strengthen with gusts around 30 kts over the northern most waters of Lake Huron as winds funnel towards the Straits. A few gusts to gales will be possible midday but are mainly expected to focus within the nearshore waters. Another high pressure then builds in through the day on Saturday and through the remainder of the weekend.

HYDROLOGY...

A cold front tracks across southeast MI this evening into the overnight hours, with numerous showers and thunderstorms expected to develop this afternoon and evening. Basin average rainfall amounts are forecast to range between 0.25 and 0.75 inches, although localized amounts of 1 to 2 inches will be possible for any areas that see repeated rounds of storms. Ponding of water on roadways and minor rises on streams and rivers will be the main impacts, but localized minor flooding in urban and low lying areas cannot ruled out.

DTX WATCHES/WARNINGS/ADVISORIES

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