textproduct: Detroit/Pontiac

KEY MESSAGES

-A Flood Watch remains in effect for wet soils, additional rainfall, and rivers at flood stage until 9 PM this evening.

-Dry on Friday before a strong cold front brings rain and a few thunderstorms late Friday night into Saturday morning.

-Breezy and much colder Sunday with a few lake showers mixing with wet snowflakes at times.

-Seasonably cold Monday morning with wind chills in the low 20s and freeze conditions increasingly likely.

DTW THRESHOLD PROBABILITIES

* Medium for ceilings aob 5000 ft early tonight.

* Medium for ceilings below 200ft or visibilities below 1/2SM late tonight.

PREV DISCUSSION

Issued at 322 PM EDT Thu Apr 16 2026

DISCUSSION...

The subtropical jet, as revealed in GOES upper level water vapor imagery, is currently positioned overhead, but will migrate eastward this evening as a shortwave trough shears into the longwave axis. CVA associated with the shorter wavelength feature ensures continued showers over the next several hours, given the tendency for forced ascent across Lower Michigan. A survey of forecast soundings suggests that narrow surface dewpoint depressions favor a period of surface-based instability this afternoon as the next infusion of ThetaE modifies moisture profiles by increasing CAPE. Effective bulk shear will be decreasing, opposite the build-up of instability. Thunder potential exists while UVVs are augmented by the system's VortMax, but the severe threat should be limited. The next round of convection has begun to percolate, but coverage should predominantly remain scattered. Since hodographs and 0-1 km SRH indicate limited capability for low-level rotation, and with PWATs dropping below 1.25 inches, the main threat should be marginally severe hail, more so for storms residing along the instability gradient, peaking near 750 J/kg (SBCAPE). Convection concludes after surface flow veers WNW and omega flips positive, by 03Z tonight.

Shortwave ridging quickly back-fills Lower Michigan tonight offering deep-layer drying and stabilization for most of Friday. A very shallow mixed-layer arises, maintaining a blanket of stratocumulus cloud, at least through midday. Winds become light and variable as the pressure gradient becomes diffuse.

Conditions deteriorate Friday night into Saturday as an amplified eastern Pacific trough phases with southern stream energy, and digs across central CONUS. Confluent lower column flow, displaced further downstream of the composite mid/upper level wave, advects moisture rich Gulf air into the Great Lakes by 03Z (Saturday) within an elevated warm frontal zone. The elongated 55-65 knot low level jet can be traced from central Ontario, back to NE Texas. This inbound air helps to quickly saturate the column, marked by an increase in PWATs of over 200 percent from 00Z to 09Z Saturday. The resulting line of showers/thundershowers should move in from the west, although the environment it moves into will be less impressive from a thermodynamic perspective. The expectation is that convection should weaken somewhat as it crosses into the forecast area, as it outruns the plume of MUCAPE that will struggle to lift into Lower Michigan.

A very strong cold front extending from the surface low over northern Lower provides the FGEN response for a secondary wave of precipitation, after the nocturnal line clears through. Lower confidence in coverage with the frontally forced showers, thunder should be limited. Sensible temperatures crash quickly behind the frontal slope with 850 mb temperatures dropping from 10C at 12Z Saturday to sub-zero (Celsius) by 00Z Saturday evening. Cold advection ensues amidst WNW flow overnight.

After a stretch of June-like weather, conditions turn reminiscent of March on Sunday as highs hold in the 40s for most. A few lake effect showers could stream into Southeast Michigan, some of which may mix in some snowflakes. A well-mixed boundary-layer supports a breezy day, gusting 25-30 mph. Potential exists for skies to clear out Sunday night, which could lead to widespread lows in the 20s. Now that the growing season is underway for most of Southeast Michigan (south of M-46), a Freeze Warning will likely be needed Sunday night into Monday morning, if current trends hold.

Height rises build in Monday as a period of ridging unfolds, before catalyzing the next warm-up after shifting to a return flow setup on Tuesday. The ridge should also help deflect several disturbances working across the Canadian Prairies mid-week.

MARINE...

Periodic rounds of showers/storms continue through the evening with an isolated severe storm possible over the southern Great Lakes. System peels away from the region late tonight ushering in a brief period of high pressure Friday bringing lighter winds and dry conditions. Broad low pressure tracking through northern Ontario will then drag a respectable cold front through the Great Lakes daytime Saturday generating yet another round of showers and thunderstorms, a few of which could be strong. Moderate to strong cold advection follows for Sunday with northwest winds peaking around 30 knots. While a couple gusts near gales are possible, overall potential remains low (<30%).

HYDROLOGY...

Given wet soils, additional rainfall, and rivers at flood stage (Tittabawassee, Saginaw, and Cass), the Flood Watch remains in effect for all of Southeast Michigan until 9 PM this evening. Additional showers continue this afternoon and evening with some thunderstorms leading to localized heavy downpours. Repeat storms over the same area could provide additional rainfall totals in excess of 1 inch, offering a heightened risk for flood sensitivity. Briefly drier conditions emerge by 03Z tonight, followed by additional rounds of showers and some thunderstorms ahead of a strong cold front late Friday and Saturday morning. Pace of additional convection should limit rainfall totals to less than a half inch.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Flood Watch until midnight EDT tonight for MIZ047>049-053>055- 060>063-068>070-075-076-082-083.

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