textproduct: Detroit/Pontiac

KEY MESSAGES

- Showers and a few thunderstorms expected this morning ahead of a strong cold front, with gusts up to 40 mph possible.

- Much colder arrives tonight through Monday. Frost/freeze conditions are likely during this period.

- Temperatures warm back toward normal Tuesday through the rest of the week.

DTW THRESHOLD PROBABILITIES

* High for ceilings aob 5000 ft this early this morning through much of this afternoon.

* Low for thunderstorms through 18z.

PREV DISCUSSION

Issued at 318 AM EDT Sat Apr 18 2026

DISCUSSION...

Pre-frontal line of showers and thunderstorms continues to fall apart, with the past hour or so of observations showing warming cloud tops, decreasing reflectivity cores, and almost a complete loss in lightning activity. This line is at the lead edge of a moisture plume that extends back to a strong cold front that will sweep through later this morning. Showers and a few thunderstorms will continue through the morning until said front comes through, some of which may produce gusty winds to 40 mph especially close to the front. High temperatures in the 60s will be observed during the morning hours, followed by quickly falling temperatures through the afternoon. Isentropic plan view shows the strongest column drying after 00z, keeping cloud cover and pockets of drizzle around through much of the afternoon. There is a sharp moisture gradient that then clears out most of the column moisture late this evening.

MOS guidance and forecast soundings both support clearing potential overnight as a major pattern shift occurs with the arrival of the thermal trough and height fall center. Dewpoints in the upper 20s and winds under 10 knots overnight support temperatures near freezing with more rural areas having potential to fall below freezing. For the daytime period, impressive surface destabilization emerges late Sunday morning. Deep layer of 7.0-7.5 C/km lapse rates up to ~15.0 kft agl generates a few hundred J/kg of MLCAPE, even as high temperatures only peak in the upper 40s. Westerly winds will become breezy (30-35 mph) in this environment. The environment will also be suitable for scattered showers (rain and snow) as wet bulb zero heights are only around 1.0 kft agl. Shower potential will be greatest in the late morning-afternoon as a low amplitude shortwave ripples overhead, adding enough moisture to engage the instability. The convective component of this setup may produce graupel/small hail and even a few rumbles of thunder.

Coldest period of the week will be Monday morning, with temperatures falling into the 20s. This will be another highly efficient radiative cooling setup, this time with H8 temperatures in the negative teens making freeze headlines likely. Despite below normal temperatures, surface high pressure affords a dry day Monday with plenty of sunshine.

As the surface high departs, southerly flow on its western flank re- establishes broad return flow throughout central CONUS into the Great Lakes region. This supports a warm up Tuesday onward, as highs climb back toward/above normal into the upper 60s-low 70s for the rest of the work week. Warm advection appears to win out against a washed out northern stream cold front that settles across Lower MI mid-week. H8 temperatures only drop briefly by a couple of degrees, while disjointed moisture supports very low end PoPs attm. A more unstable pattern then develops toward the end of the work week.

MARINE...

Early morning southerly winds peak 25-30kts as remnant convection ahead of an approaching cold front cross the central Great Lakes. A couple gusts to or above 34kts are possible as storms move in and weaken overlake thermal stability. Front eventually crosses late morning flipping flow to the west-northwest with gusts along and in the immediate wake of the front likewise able to peak around 25- 30kts. While a modest weakening of wind (lowering 10kts or so) occurs for the evening due a weakening gradient, the arrival of the main core of the colder trailing airmass Sunday reinvigorates northwesterly winds supporting another period of gusts near 30kts. Small Craft Advisories remain in effect around the Thumb through this evening as a result of the stronger winds/higher wave action with another period of advisories potentially warranted latter part of Sunday over the same waters. Strong high pressure then slides across the central Great Lakes for Monday.

HYDROLOGY...

A cluster of showers and a few thunderstorms will track across the region this morning ahead of a strong cold front. Rainfall amounts are expected to hold between a quarter to half inch. In light of recent rains and saturated soils, any additional rainfall may lead to some ponding or localized minor flooding. Current projections suggest any higher rainfall amounts will be too localized to worsen ongoing river flooding across the Saginaw Basin.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422.

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

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