textproduct: Detroit/Pontiac

KEY MESSAGES

-Persistent Flood Risk: A Flood Watch remains in effect through Thursday night as multiple rounds of showers and thunderstorms cross a stalled frontal boundary. Previous rainfall has saturated soils, making the region highly susceptible to additional runoff.

-Severe Potential: A Marginal to Slight Risk for severe thunderstorms exists this afternoon and evening, with another isolated threat focused toward the Michigan/Ohio border on Thursday. The primary hazard remains damaging wind gusts within any organized convection.

-Dry Friday followed by a Cold Weekend: Conditions dry out briefly on Friday before a strong cold front brings rain and possible thunderstorms on Saturday. The weekend concludes on a windy and much colder note Sunday, with temperatures plunging into the 40s.

DISCUSSION

A stalled-out frontal boundary remains draped across southern Lower Michigan early this morning. Water vapor imagery reveals at least two distinct upper-level waves currently over the Plains that are progged to work through the Great Lakes region through Thursday night.

The 00z RRFS and 00z 3KM NAM both provided a reasonable depiction of the convective line that rolled through Southeast Michigan earlier this morning. However, notable differences remain regarding the timing and extent of redevelopment today. Leaning toward the RRFS solution, expect a brief lull by mid-morning as the initial wave exits. This reprieve will be short-lived, as high-resolution guidance suggests rapid airmass recovery by early afternoon. With SBCAPE progged to rebound into the 1000 - 1500 J/kg range amidst 40- knot bulk shear, additional discrete cells or multicell clusters are favored to develop along residual outflow boundaries. The Day 1 SPC outlook maintains a Slight Risk for southern areas, with damaging wind being the primary hazard.

The RRFS remains aggressive for Thursday as well, highlighting a secondary mid-level trough lifting into the Great Lakes. This feature will provide stronger synoptic forcing for widespread, efficient precipitation. Relief finally arrives on Friday as a transitory period of mid-level ridging and surface high pressure provides a much-needed reprieve from the active weather.

Attention then turns to a potent longwave trough ejecting out of the Pacific Northwest and arriving over the weekend. A deepening surface low is progged to track through the Upper Mississippi Valley on Friday, dragging a cold front through Southeast Michigan on Saturday (most likely during the early afternoon per the 00z Euro). Any delay in frontal timing could allow for stronger southwest winds ahead of the boundary, with gusts potentially reaching 40 mph given the 40 - 50 knot jet at 850 mb. While widespread showers may help limit instability - keeping MUCAPE values under 1000 J/kg - the strong wind fields will maintain a marginal severe threat.

Post-frontal cold air advection (CAA) looks robust for the tail end of the weekend, with 850 mb temperatures bottoming out around -10C by Sunday morning. Breezy to windy conditions will make for a "raw" day, as highs struggle to exit the 40s under a persistent deck of stratocumulus. Steep low level lapse rates will also support isolated to possibly scattered rain or snow showers through Sunday afternoon.

MARINE

Overnight showers and thunderstorms depart this morning while an unsettled pattern remains in place today and Thursday. Additional rounds of showers and storms are possible throughout the day, with similar strong to severe concerns as the past few days. Localized winds in excess of 35 knots, erratic waves, and large hail will all be possible. Familiar wind pattern today and Thursday as the warm front holds near Saginaw Bay, causing winds to back toward the east north of the front. Some relief to the wet pattern is expected Friday before another low ripples through Saturday, drawing a strong cold front across the region. This will elevate winds on a more widespread basis compared to the more localized wind potential in thunderstorm activity through the work week.

HYDROLOGY

Rainfall totals up to 2 inches were observed earlier this morning across portions of the M-59 corridor and the Saginaw Valley. Given this antecedent rainfall and already saturated soils from a wet spring, the Flood Watch remains in effect for all of Southeast Michigan through Thursday night. Significant rises are expected on regional waterways, with the Tittabawassee and Saginaw Rivers forecast to reach flood stage; the Shiawassee River also remains a point of concern for potential flooding.

Multiple rounds of showers and thunderstorms will continue intermittently through Thursday evening. While broad-scale forecasted rainfall totals today through Thursday are generally around 1 inch, which typically would not trigger widespread flooding. Any focused areas of convection could significantly over- perform. The primary concern is for thunderstorms to "train" over the same localized areas, leading to much higher rainfall totals and a heightened risk for flash flooding. Confidence in the exact timing and placement of these heavier corridors remains low, but the overall environment remains highly conducive to efficient rainfall rates.

PREV DISCUSSION

Issued at 159 AM EDT Wed Apr 15 2026

AVIATION...

Strongest line of convection has passed through PTK southward and will impact the Detroit taf sites for the first hour or two of the forecast. TSRA may continue a bit after that within the trailing stratiform before showers taper off around 10-12Z. Warm front remains draped across the area with potential showers and thunderstorms today and into tonight. Tried to time out some higher confident windows of time based on hires models, but those times may shift. Outside of variable winds during convection, they should largely be southwesterly around 10 knots.

DTW/D21 Convection... A line of thunderstorms will move across DTW between now and 09z. Showers will continue with some embedded thunder possible through the early morning. After a potential brief lull, additional rounds of showers and thunderstorms will exist through the day.

DTW THRESHOLD PROBABILITIES...

* High for ceilings aob 5000 ft tonight. Medium Wednesday morning.

* Medium to high for thunderstorms tonight between 04z and 09z.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Flood Watch through late Thursday night 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.