textproduct: Detroit/Pontiac

KEY MESSAGES

- A broken line of thunderstorms tracks through SE Michigan between 4 PM and 9 PM this evening. A few strong to severe storms are possible.

- An isolated shower is possible Thursday afternoon, then drier and less humid conditions are expected through Friday and Saturday.

- A warming trend brings above normal temperatures early next week.

DISCUSSION

A couple of thunderstorm clusters have developed over western Lower Michigan this afternoon along a continuous line of agitated cumulus that stretches from northern MI back toward central Illinois. The trend so far has been for cells to be short-lived as they move off the boundary and away from the instability axis, which is anchored closely to the cold front itself. Local cloud trends are quite stable still, reflecting remnants of the 850-600mb stable layer that was sampled in the 12z KDTX sounding.

Expectations for the afternoon-evening are still largely on track where coverage increases to become a broken line of showers and storms. Any deeper convective growth is likely confined to a window of about 4pm-9pm as moisture convergence sweeps through ahead of the front and overlaps with weakening shear profiles. The lack of deep layer shear favors a pulsey/multicellular nature rather than strong cold pool organization, meaning isolated downburst and hail potential as cores collapse. Given the environment, higher confidence in a strong-severe storm exists near the Ohio border where instability is greatest although all of SE MI is in at least a Marginal Risk for severe weather. Veered south/southwest flow is generally less favorable for the streamwise vorticity needed for tornadoes with a west-east mean wind. That said, there has been weak mid-level rotation noted upstream so cannot rule out supercellular structures, mainly early on as shear is at its peak.

The cold front sweeps through late this evening, bringing an end to thunderstorm chances overnight. A quieter pattern then develops Thursday into the weekend as surface high pressure fills in post cold front. Northwest flow and return of thermal troughing take advantage of warmer lake temperatures to generate partial coverage of stratocumulus Thursday, which could squeeze out low-topped shower activity. Moisture availability then wanes Friday into the weekend as the high drifts overhead, with winds then shifting to the southwest by Saturday in response. Dry conditions thus expected. Coolest high temperatures of the period expected Thursday-Friday as h8 temperatures drop into the lower teens across Lower MI, equating to highs in the upper 70s and lows in the 50s.

The emergence of SW flow Saturday then kicks off a warming trend that peaks early next week. GFS and Euro MOS guidance are in line with the extended NBM, projecting high temperatures near 90 degrees Monday-Tuesday. This pairs with a gulf connection where moisture transport is accelerated Sunday through Tuesday as low level jet winds increase to 30-35 knots. This establishes breezy southwest flow (~25 to 30 mph) during peak heating each day, as well as an increase in shower and thunderstorm chances across the Great Lakes.

MARINE

Scattered showers and thunderstorms work across the area this evening in advance of an approaching cold front. An isolated strong wind gust is possible particularly towards the southern Great Lakes. Cold front eventually crosses the region late evening-tonight flipping around winds to the NW for Thursday. Moderate cool advection follows with peak gusts between 20-25kts over the northern portions of Lake Huron daytime Thursday before high pressure begins to build in. Said high then drifts overhead Friday and Saturday.

PREV DISCUSSION

Issued at 1240 PM EDT Wed Aug 26 2026

AVIATION...

South-southwest winds around 10 knots and VFR Cu will prevail this afternoon ahead of a cold front, which will continue to trigger scattered to numerous showers and thunderstorms as it passes through southeast Michigan early his evening. Adjusted timing of possible thunderstorms a bit earlier based on current trends and attempted to narrow the time range, as storms look progressive tracking east; activity should exit all taf sites by mid-evening. Expect a dry slot and partial clearing through the rest of the evening and most of the night. However, light west-northwest cold advection flow will likely be sufficient for low clouds (borderline MVFR/VFR) to spread into the northern taf sites by sunrise Thursday, and then into southern sites later in the morning before cloud bases rise and clouds scatter out in the afternoon.

D21/DTW Convection...A thunderstorm or two is likely to pass through the Detroit airspace between 21-01z.

DTW THRESHOLD PROBABILITIES...

* Low-Medium for thunderstorms late this afternoon/early evening.

DTX WATCHES/WARNINGS/ADVISORIES

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

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