textproduct: Detroit/Pontiac

KEY MESSAGES

- Becoming more humid today with afternoon/evening showers and thunderstorms likely. 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.

UPDATE

Low pressure is observed over central Lake Superior this morning, with its cold front extending south across Lake Michigan. Two distinct cloud bands seen on satellite are actively producing showers with a more isolated degree of convection noted. Minor update to the forecast to include slight to chance PoPs north of I-69 this morning for the leading band of showers.

The trailing cloud band, more closely associated with frontal forcing and moisture convergence, will be the feature to watch late this morning into the afternoon for thunderstorm development over west MI. Already seeing cloud-top cooling and growing radar returns along this feature, which reaches SE Michigan this afternoon. The main limiting factor is that instability is anchored to the front, and storms are moving off of that boundary into a drier and more stable environment. General expectation is thus for storms to flare up and form a broken line, although the coverage and longevity of individual cells may struggle with how narrow the instability axis is. No major changes to the 4am package regarding our severe chances or timing, with all hazards in play and timing focused around 3pm-9pm (slightly earlier in the Tri Cities).

PREV DISCUSSION

Issued at 647 AM EDT Wed Aug 26 2026

AVIATION...

Surface high pressure will maintain dry air in the lowest 12.0 kft agl through the early afternoon hours today. Height falls and southerly flow ahead of northern Great Lakes shortwave will eventually draw moisture northward late this afternoon supporting the potential for scattered showers and thunderstorms. Most likely time window is 19z to 01z from north to south with brief MVFR to IFR visibility restrictions possible.

D21/DTW Convection...Scattered thunderstorms will be possible in the airspace between 22-01z.

DTW THRESHOLD PROBABILITIES...

* Medium for thunderstorms Wednesday afternoon-evening.

PREV DISCUSSION... Issued at 339 AM EDT Wed Aug 26 2026

DISCUSSION...

Last vestiges of upper shortwave ridging are departing this morning, with remnant warm mid levels maintaining stable conditions through noon. A closed upper low over the arrowhead of MN is on track to pass across Upper MI later today, opening into a trough in the process. Weak moisture transport ensues on modest S to SW wind, culminating in a more humid day with dew points creeping into the mid to upper 60s by this afternoon. As the upper trough erodes the remnant stability, showers and storms should percolate along a surface trough into west MI late this morning. Relatively weak divergence aloft and gradual height falls provide support for ascent as convection spreads eastward along the lead edge of the inbound low-level theta-e ridge, bringing fairly high confidence (60-70%) for showers and thunderstorms this afternoon and evening. Timing in hi-res guidance continues to favor arrival into the Tri-Cities around noon to 3pm, then the rest of SE MI between 3pm and 10pm.

HREF shows mean SBCAPE of 1000-1500 J/kg building in but with convection generally outpacing the higher instability as the evening goes on. Bulk wind shear on the order of 25-30 kt will offer potential for marginal updraft organization and a window for isolated stronger to severe storms. A band of slightly higher SW 850mb flow will accompany the trough, enlarging low level hodographs to some degree especially if surface wind remains backed/southerly. Damaging wind gusts will be the primary threat in the strongest storms, but large hail and a weak tornado will also be possible if any supercellular structures emerge. Hi-res ML guidance continues to favor areas south and west of SE MI for this threat, and will note that neighborhood probabilities for all severe hazards have decreased in 00z HREF. The SWODY1 slight risk area south of I-96 is driven by 15% wind probs, with hi-res reflectivity suggestive of transient linear features in this area. Localized heavy downpours will be possible as PWAT flirts with the 90th percentile around 1.50", but ensemble QPF data do not indicate a broader excessive rainfall threat.

A lull in convection is anticipated by late evening as the initial surface trough works eastward, but lingering instability ahead of the cold front will offer potential for additional spottier showers and perhaps a thunderstorm into the early overnight. The cold front then passes through early morning to end precip chances. The inbound air mass is not much different in temperature but slightly less humid. Weak instability develops on Thursday as longwave troughing induces steeper lapse rates aloft - this fuels ~20% probability for isolated late afternoon and evening showers.

A secondary cold front drops through ahead of high pressure that builds in through Friday and Saturday. This brings pleasant and less humid conditions with lots of sunshine. By early next week, the subtropical ridge over the southern Plains is progged to migrate into the Tennessee Valley. Warmer southwest flow riding in north of the ridge will bring a warming trend next week with the latest NBM advertising a 40-50% chance for parts of SE MI to see highs in excess of 90 degrees Monday and Tuesday.

MARINE...

Southwest flow becomes well established across the Great Lakes today as a high pressure system departs into the continental northeast. An approaching cold front will strengthen the pressure gradient ahead of this front, increasing wind speeds through the day. Wind gusts of 20 to 25 knots will be likely across Saginaw Bay given the favorable fetch, where Small Craft Advisories are in effect.

Showers and thunderstorms will also become increasingly likely with the passage of the front, including a low chance for isolated strong thunderstorm development capable of producing wind gusts aoa 34 knots. Winds veer to the northwest after the frontal passage with northwest flow holding on through tomorrow. High pressure fills back in Friday and Saturday.

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.