textproduct: Detroit/Pontiac

KEY MESSAGES

-A Flood Watch remains in effect through tomorrow night with multiple rounds of showers and thunderstorms; some rivers are expected to reach/exceed flood stage.

-A Marginal Risk for isolated severe weather tomorrow south of I-69.

-Conditions dry out briefly on Friday before a strong cold front brings rain and possible thunderstorms on Saturday.

-Turning windier and much colder Sunday, with temperatures plunging into the 40s; a few snowflakes are possible.

DTW THRESHOLD PROBABILITIES

* Medium for ceilings aob 5000 ft after 06Z tonight. * Low for thunderstorm tonight.

PREV DISCUSSION

Issued at 359 PM EDT Wed Apr 15 2026

DISCUSSION...

An active stretch of convection continues this afternoon and evening as the next round of thunderstorms move through Southeast Michigan. The primary stalled frontal boundary remains hung-up over northern Lower Michigan with dewpoints in the 40s, while downstate values are much higher, mostly in the 60s. This warm/moist airmass holds while a secondary, more subtle, convergence axis has become the area of greater concern for additional convective development, positioned from northern Indiana into the southern Ontario peninsula. Forecast soundings have hinted at some low-level CIN as weak capping in the 3- 5 kft layer tries to emerge, but CI over southern Monroe county proved that some surface-based parcels are still able to capitalize on potential instability. Extensive cloud cover limits deeper CAPE density, but fresh updrafts have managed to emerge along the boundary.

A remnant MCV moving across the Tri-State area at press time follows a similar trajectory as it brushes southern Lower, and should maintain integrity given ambient shear and ThetaE convergence. A Slight Risk remains outlooked for much of Southeast Michigan by SPC, but the emphasis will be on locations south of I-94 where instability is maximized. Strong gusts and large hail are the anticipated severe hazards, but a weak tornado threat remains given 100+ m2/s2 of 0-1 km SRH, and persistent rotation from the inbound MCV (and vicinity storms). Further north, expect scattered coverage with a lesser concern for severe. Slightly higher risk for a few additional strong storms exists over the Tri-Cities and Thumb region this evening with the arrival of higher MUCAPE bubble. Mild again tonight with lows only in the 60s.

More showers and thunderstorms develop overnight as the southern stream jet positions atop the Great Lakes with several perturbations rippling through. Healthy 0-6 km bulk shear of 40-50 knots will be available tonight, with some linearity in convective mode arising at times. Mixed signals exist regarding the prevalence of surface mixing potential, or if a weak nocturnal inversion can hold to keep convection more elevated. Very minimal change noted in mid-level temperature profiles tonight, but layer dewpoints/PWATs should rise supporting heavy rainfall rates, given increasing background tendency for synoptic ascent. Mid-level lapse rates remain below 6.5 C/km.

Latest CAMs offer little clarity in timing a reprieve from convection on Thursday, therefore, early morning, late morning, and afternoon convective potential exists. Shortwave trough feature embedded within the mean flow slides through aloft between 15Z and 21Z. This provides a boost in CVA, leading to low-end severe potential, limited by instability. Shortwave ridging then slides in Friday with high confidence in a mainly dry day. Amplified longwave trough of eastern Pacific origin reaches Lower Michigan Friday night, favoring anomalous warmth, convection, and breezy conditions. The system forces a stark cold front through Saturday sending 850 mb temperatures crashing into the minus teens (Celsius). A transition to light snow showers is possible Sunday morning with post-frontal northwest flow and ensuing cold advection to close out the weekend.

MARINE...

Active pattern remains firmly in place as additional scattered areas of showers cross the region this evening. Thunderstorm potential is highest across the southern half of the area, particularly over the southern Great Lakes where a few strong to severe storms are possible (wind gusts in excess of 34kts being the primary hazard though some large hail or an isolated waterspout are possible). Trough moves into the area by Thursday maintaining periodic rounds of showers/storms. System peels away from the region by Thursday night 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, some of which have the potential to be severe. Moderate to strong cold advection follows for Sunday with northwest winds peaking in the lower 30s. While a couple gusts near gales are possible, overall potential is lower (<30%) at this time.

HYDROLOGY...

Given 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, Saginaw, Cass, and Shiawassee Rivers forecast reach/exceed flood stage.

Multiple rounds of showers and thunderstorms will continue through Thursday evening. While broad-scale forecasted rainfall totals today through Thursday are generally around 1 inch, any focused areas of convection could significantly over-perform. The primary concern is for thunderstorms to train, leading to much higher rainfall totals and a heightened risk for worse flooding. Confidence in the exact timing and placement of these heavier corridors remains low tonight and Thursday, but the overall environment remains highly conducive to efficient rainfall rates. Afternoon rainfall rates have ranged between approximately 1 and 2 inches.

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.