textproduct: Detroit/Pontiac

KEY MESSAGES

- Showers and scattered thunderstorms are expected through this morning.

- Much colder air will advance into the region Saturday into Sunday. There is a chance of showers Sunday afternoon. Frost/freeze conditions are likely Sunday night.

DTW THRESHOLD PROBABILITIES

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

* High for thunderstorms between 07-11z this morning.

PREV DISCUSSION

Issued at 306 PM EDT Fri Apr 17 2026

DISCUSSION...

The lingering influence of mid level ridging and surface high pressure over the eastern Great Lakes will sustain dry conditions through the evening. Attention then turns to ongoing upscale convective growth across the upper Mississippi Valley. This convection is occurring within a region of rapid destabilization ahead of a long wave trough and associated surface cold front. The 12Z hi res guidance continues to suggest this convection outpacing sfc instability advection as it tracks across Lower Mi overnight. Model soundings/plan views do however show an axis of elevated instability tracking across Se Mi in the 06Z to 12Z time frame along the lead edge of convectively induced short wave impulses. This will warrant high chances of showers and thunderstorms. There has been a weakening trend in forecast elevated instability, thus mitigating the severe weather risk in line with the SPC Day1 outlook. Mid level thickness diffluence may result in some training, however the progressive nature of the short wave impulses will limit the risk of excessive rainfall overnight.

While the plume of elevated instability will exit east of the forecast area shortly after 12Z Saturday, the main sfc cold front is forecast to lag the elevated instability axis, advancing across Se Mi late in the morning. Boundary layer convergence is shown by several hi res solutions to result in a line of showers along the front. Despite the shallow nature of this convection, some localized gusty winds can not be ruled out. This front will mark a notable airmass change across the region as the advancing longer wavelength trough drives much colder and drier air across the Great Lakes this weekend. 850mb temps will plunge into the negative single digits by Saturday evening. Post frontal sfc temps will gradually drop into the 40s Sat aftn/evening. While lows are expected to dip down into the 30s Saturday night, the WNW gradient winds will limit the frost potential.

There is reasonable model agreement in showing a mid level short wave impulse traversing srn Mi Sunday within the base of the longer wavelength trough. The region of ascent will be concurrent with diurnal heating/instability. A mid level cold pool will also contribute to steep mid level lapse rates. This will warrant a chance of convection, possibly limited in coverage by extremely dry air in the sub cloud layer. Steep low level lapse rates will boost afternoon highs well into the 40s, keeping precip type mainly rain. Weak instability with convective cloud depths likely reaching the minus 20C isotherm may support some thunder and small hail. If some heavier convective elements materialize, a brief interval of wet snow can not be ruled out. The passage of this wave will result in a reinforcing shot of cold air. Ensemble guidance indicates a high likelihood that Sunday night low temps will drop into the mid to upper 20s as high pressure expands overhead. Some moderate in temps is forecast early next week. Ensemble members suggest any precip associated with a secondary cold front mid week will be light given the overall limited moisture.

MARINE...

Winds organize and strengthen out of the southeast this evening in response to low pressure tracking into northern Ontario. Moderate southerly winds with peak gusts in the 25-30kt range expected tonight before flipping to the west-northwest daytime Saturday with the passage of a respectable cold front. Gusts along/immediately following the front top out around 30kts. Another round of showers and thunderstorms are likely in advance of said front. Core of the colder trailing airmass arrives Sunday reinvigorating northwesterly winds supporting another period of gusts around 30kts. While a couple gusts near gales are possible, overall potential remains low (<30%). Small Craft Advisories are in effect around the Thumb late tonight into Saturday as a result of the stronger winds/higher wave action with another period of advisories looking warranted latter part of Sunday. Strong high pressure then slides across the central Great Lakes for Monday.

HYDROLOGY...

A cluster of showers and scattered thunderstorms are forecast to traverse the region overnight into early Saturday morning. Recent model guidance have trended a little weaker with the overall convection. Current indications are for high probabilities for 12 hour rainfall amounts in the quarter to half inch range, with less than 30 percent probabilities for rainfall totals of three quarters to one inch. In light of recent rains and saturated soils, any additional rainfall may lead to some 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.