textproduct: Detroit/Pontiac

KEY MESSAGES

- Showers and thunderstorms tonight will pose an isolated risk for severe weather.

- Additional scattered showers and thunderstorms on Tuesday, then mostly dry conditions with temperatures dipping below average during the mid to late week period.

DTW THRESHOLD PROBABILITIES

* Low in thunderstorms overnight and Tuesday morning.

* Low for westerly crosswinds Tuesday afternoon.

PREV DISCUSSION

Issued at 857 PM EDT Mon Jul 20 2026

UPDATE...

A cluster of storms stretching from the eastern UP into NE Wisconsin is tied to a region of coupled upper divergence/low level convergence along the lead edge of an instability gradient. This dynamically driven region of ascent will drift across northern Lower Mi tonight. It is notable that convection has been struggling between these storms and the MCS now over Iowa and NW Illinois. Regional ACARS soundings indicate a mid level warm layer across southern Wisconsin, likely providing enough inhibition to limit convection in this area. The 00Z DTX sounding also had respectable amount of warm air in the mid levels. This is likely to also result in some limit of convective potential across Se Mi during at least the early portion of the overnight hours as the aforementioned larger scale forcing resides to the north. Regional water vapor imagery indicates some mid level short wave energy advancing into Minnesota, expected to rotate into central Lower Mi late tonight and early Tues morning, which should offer a more notable erosion of the mid level warm layer. This feature will also coincide with the lead edge of the elevated instability axis. Given this and regional radar trends, timing of the better convection chances have been pushed back later into the night. Given the degree of forecast elevated instability and steep mid level lapse rates, an isolated severe risk late tonight can not be ruled out.

PREV DISCUSSION... Issued at 351 PM EDT Mon Jul 20 2026

DISCUSSION...

Benign conditions carry through the afternoon and evening as stability holds within the warmer return flow of high pressure now exiting off the Mid-Atlantic coast. Smoke models and AQI observations indicate the remnant wildfire smoke will linger across the region, but EGLE forecasts call for concentrations to gradually decline so the Air Quality Alert will be allowed to expire tonight.

A favorable setup for severe weather is in place over Wisconsin and the western UP this afternoon and evening as a potent shortwave pivots across the northern Great Lakes. Potential for supercells exists west of Lake Michigan with anticipated evolution into a broken line or clusters of storms that migrate E to ESE into the lower peninsula late this evening. The best synoptic/upper jet forcing driving this convection is slated to pass overhead between 02z and 10z tonight, outpacing the narrow plume of upstream instability that will lag behind. Remnant low-level stability noted in model soundings and the nocturnal timing devoid of surface-based instability likely result in a weakening trend as convection arrives late this evening, and a transition of surviving convection to an elevated character. Peak coverage is anticipated between midnight and 6am, with scattered to numerous showers and embedded thunderstorms. The main threat would be isolated wind gusts in excess of 40 mph, but this carries low confidence given the near- surface stability. If upstream convection holds together and marginal instability works into the western Saginaw Valley late this evening, this would be the most likely area to see severe wind gusts. A Marginal Risk for severe weather and excessive rainfall exists across the area tonight.

A pocket of forced ascent along the LLJ passes over the southern forecast area between 12z and 15z Tuesday morning which offers potential for a flare-up of showers/storms, but latest CAM output suggests the higher potential for convective response may ride the CAPE gradient and track farther south into IN/OH. Otherwise, increasing low-level moisture and steepening mid-level lapse rates cause a plume of instability to spread across Lower MI Tuesday morning ahead of the cold front set to track through in the late afternoon. This is sufficient to maintain a chance of scattered showers and thunderstorms, especially across the Thumb. Will monitor areas east of I-75 for isolated strong to severe storms in the early afternoon while instability and shear briefly reach a peak. Breezy conditions amidst cold and dry advection ensue behind the front with 850mb temps falling to around 5C Wednesday morning, translating to lows in the mid 50s.

Cool and dry conditions prevail Wednesday and Thursday as high pressure eases across the region, with high temps in the 70s and lows in the 50s. Dry conditions persist into Friday with an uptick in temperatures closer to the seasonal average as southerly return flow ensues. The next window for more active weather looks to arrive late in the weekend as the next cold front sweeps across the Great Lakes.

MARINE...

Low pressure tracks across Ontario and into Quebec through the first half of the week, establishing an active pattern across the Great Lakes. Breezy southwest flow has already started to develop ahead of a cold front that will track through late tonight into Tuesday morning. A line of thunderstorms is expected with the frontal passage, tracking across northern Lake Huron this evening and into Lake Erie by early Tuesday morning. Greatest potential for strong to severe intensity will be over north/central Lake Huron this evening, where damaging wind will be the main threat. Scattered thunderstorms then remain possible Tuesday until a second front swings through in the evening, shifting winds from west to northwest and providing a brief opportunity for gale force gusts centered around 00z (8pm local). Short duration gust potential precludes headlines at this time, although a short-fused warning is plausible Tuesday evening if observations warrant. Breezy northwest flow then persists through mid-week although with drier conditions as high pressure builds in. Small Craft Advisories are in effect through Wednesday, with beach hazards concerns for Tuesday-Wednesday as well.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory until 10 PM EDT Wednesday for LHZ421.

Small Craft Advisory until 4 PM EDT Wednesday for LHZ422.

Small Craft Advisory from 4 AM Tuesday to 10 PM EDT Wednesday for LHZ441>443.

Lake St Clair...Small Craft Advisory from 4 AM to 10 PM EDT Tuesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 4 AM to 10 PM EDT Tuesday for LEZ444.