textproduct: Detroit/Pontiac

KEY MESSAGES

- Non-zero chance of an isolated thundershower near the Ohio Border this evening; mainly dry conditions prevail elsewhere.

- Shower and thunderstorm chances return Friday night through Saturday.

- Turning a bit cooler Sunday and Monday with a drying trend before warming up toward the middle of next week.

DTW THRESHOLD PROBABILITIES

* None.

PREV DISCUSSION

Issued at 349 PM EDT Wed Aug 19 2026

DISCUSSION...

Frontal progress has slowed significantly this morning, becoming stationary near the Ohio border. This convergence zone could support a few additional showers (and perhaps a rumble of thunder) through the evening hours as PWATs and low-level moisture remain marginally supportive, but subsidence layers and some evidence of capping inhibit any broader convective response. Afternoon KDTX radar has been relatively quiet, with one exception over The Thumb where lake breeze boundaries have triggered some isolated pulse convective showers. Elsewhere, the post-frontal airmass leads to steady lowering of dewpoints, from the 60s down into the 50s. The pressure gradient should stay diffuse, in the absence of a well-defined surface high pressure center over the Great Lakes region. Flow should turn northerly tonight and trend toward calm. Seasonably cool temperatures expected overnight with lows dipping into the 50s, capped to the low side by mixed cloud cover.

The broad upper low centered within resident composite longwave troughing dislodges eastward Thursday, exiting James/Hudson Bay into northern Quebec. Cyclonic flow will persist aloft over Southeast Michigan for most of Thursday, but low-level anticyclonic influence becomes more established, building from the eastern Plains. Expect standard late August conditions with a dry forecast, highs near 80F, afternoon dewpoints mixing into the mid (or perhaps low) 50s, and overnight lows in the upper 50s. The embedded jet streak departs Friday leading to split-flow aloft, albeit within a broader CONUS trough configuration. Column winds turn zonal from 700 mb upwards, while Pacific shortwave energy works across the High Plains toward Lower Michigan. Low-level jet response appears in the progs, becoming southwesterly within the lowest 4 kft by midday Friday. This ushers in renewed ThetaE convergence priming the boundary layer for the next round of showers and storms. Latest model data suggests precipitation should hold off during the daylight period Friday.

The surface low is set to track across northern Michigan late Friday and Saturday with rain focused along the attendant cold front. Timing differences persist per NWP solutions. A secondary and more progressive wave will speed across central Ontario, phasing with the lead wave by Saturday evening. This leads to a reinforcing shot of cooler air and shower chances early Saturday night. Thermal troughing then fills in by Sunday morning, dropping 700 mb temperatures near/below 0C (omitting the GFS/GEFS). CMC/ECMWF even hint at lake effect (rain) shower potential amidst cold cyclonic northwest flow. 1020 mb surface ridge builds south from Manitoba/Ontario early next week, before return flow arrives and lifts readings back above normal toward the middle of next week.

MARINE...

Tonight into tomorrow afternoon a high pressure develops over the region, thus bringing light varying winds and calm weather. Thursday Evening the wind direction is expected to veer from Northern to Easterly throughout the evening to overnight hours across all regions. Northerly flow of 10 knots, with gusts up to 15 knots, possible across all regions late Thursday afternoon. Gusts up to 20 knots will possible in the bay area in the late evening hours as well. Friday a high pressure system departs our area as a low pressure system, and associated cold front, approaches the region. A pressure gradient between systems enhances southeasterly wind flow all afternoon for Northern Lake Huron and in the evening hours for the Bay area and Southern Lake Huron. Moderate winds up to 15 knots, with gusts up to 20 knots, possible Friday evening in Lake Huron and Bay area. A chance for rain showers, and possibly a thunderstorm, are possible for all regions Friday evening. Active weather continues through Sunday before clearing up to begin the week.

DTX WATCHES/WARNINGS/ADVISORIES

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