textproduct: Detroit/Pontiac

KEY MESSAGES

- Mostly dry the rest of today, although an isolated shower or thunderstorm cannot be ruled out before 9 PM.

- Above normal temperatures continue today and Friday with highs in the 70s.

- A frontal boundary tracks across Lower Michigan Friday evening leading to widespread showers and thunderstorms; isolated gusty winds of 50+ mph and hail near 1 inch possible.

- Becoming drier over the weekend with highs falling into the 50s and 60s.

- Showers and thunderstorms return Monday night into Tuesday with a return to above normal temperatures.

DISCUSSION

The longwave ridge axis currently bisecting Lower Michigan will begin to evolve from its omega block state tonight. A speed max within the base of an upper low parked upstream will interface with a southern stream jet streak over the Four Corners region, causing the ridge to compress laterally. Meanwhile, lower column dynamics displaced east of the closed wave aloft support the advection of higher ThetaE air into the region, but system-relative anticyclonic isentropic descent creates unfavorable conditions for destabilization. Forecast soundings this evening do indicate potential for meager SBCAPE amidst tenuous cap near 7 kft, but poor mid-level lapse rates and aforementioned drying processes preclude any upward revisions to PoPs, currently capped at 10 percent. Should an updraft break through the cap, it would most likely occur from 22- 01Z, as a short-lived single-cell thunderstorm. Mild temperatures are forecast overnight, in the 50s (or about 10F above climo) which are the result of increasing nocturnal cloud fraction and warm advection.

Broadening of the adjacent upper lows causes vorticity to gradually extend into southern Lower with time on Friday. The system's surface low(s) track northeast across the state with pre-frontal troughing touching off some showers Friday morning. Some residual weak elevated instability with MUCAPEs up to 100 J/kg could increase the productivity of a few showers, therefore, increased PoPs from dry to areas of Chance from 12-14Z. A midday lull in precipitation is expected prior to the arrival of the cold front during the afternoon and evening hours.

The front will likely still be over Lake Michigan by 18Z Friday, based on the location of progged surface troughing/wind shift, but warm sector instability will be building as moisture transport maximizes. As expected, Hi-Res model space varies greatly in coverage and intensity with the presence of preexisting convection, new CI, and coverage as stronger dynamic support lags. The front then progresses through Southeast Michigan by 00Z Friday evening offering higher confidence in broader coverage of showers and thunderstorms. Areas west of US-23 are more likely to experience strong to marginally severe storms as instability maximizes, and better shear values ensue. Gusty winds of 50+ mph and hail near 1 inch are possible. Although storms may become better organized, linearly, as convection moves eastward late Friday evening, intensity should be declining. Winds shift from SSW to WNW behind the front Friday night with a muted thermodynamic response as occlusion processes proceed.

Broad range of high temperatures Saturday with flow turning northeasterly making for cooler conditions inland from Lake Huron, while influence will be less prominent toward the southeast. 850 mb temperatures closer to 10C reside near an inversion layer below 800 mb. No major precipitation concerns given ample mid-level dry air and PWATs dropping to around 0.40 inches. A few showers are possible depending on the emergence/positioning of a deformation axis over Lakes Superior and Huron. Afterwards, the western Canada cyclonic wave retrogrades while the other to east releases into the northern Atlantic leaving the Great Lakes within a weaker flow-field with shortwave ridging overhead. This persists through Sunday with the next chance for showers/storms late Monday into Tuesday with the arrival of a sharpening shortwave trough within an amplifying southern stream wave. Deterministics indicate surface central pressure dropping to 990 mb.

MARINE

The central Great Lakes will continue to hold under high pressure this afternoon maintaining benign marine conditions. A warm front will continue to move over southern portions of the Great Lakes this evening. A low pressure system will develop over the upper Midwest and pushes in to the Great lakes Friday night into Saturday. This will bring chances for widespread showers and thunderstorms during this time. Ahead of the low on Friday, southeasterly winds strengthen with gusts around 30 kts possible over the northern waters of Lake Huron as winds funnel towards the Straits. Another high pressure then builds in later this weekend.

HYDROLOGY

A frontal boundary tracks across the Great Lakes Friday afternoon through the overnight hours. Basin average rainfall amounts are expected to be between 0.25 and 0.75 inches, although localized amounts over one inch remain possible, especially for areas experiencing repeated rounds of showers/thunderstorms. Ponding of water on roadways and rises on area rivers will be the main impacts, although localized minor flooding in urban and low lying areas cannot ruled out.

PREV DISCUSSION

Issued at 139 PM EDT Thu Apr 23 2026

AVIATION...

A general area of subsidence held within prevailing high pressure will maintain VFR conditions through tonight. A gradually destabilizing diurnal environment will support some degree of higher based cu development thru early evening. A very low probability /less than 10 percent/ exists for s shower or thunderstorms to materialize within this environment through the evening hours, but chances remain too remote to highlight attm. Limited cloud coverage likely tonight as attention turns to the higher plume of moisture expected to accompany a cold front Friday. Thicker mid cloud will arrive Friday morning, with a low probability for some widely scattered showers. Greater convective potential will exist Friday mid afternoon into the evening hours.

DTW THRESHOLD PROBABILITIES...

* Low for thunderstorms Friday afternoon.

DTX WATCHES/WARNINGS/ADVISORIES

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