textproduct: Detroit/Pontiac

KEY MESSAGES

- There is an isolated risk for strong to marginally severe thunderstorms this morning and again early this afternoon with the arrival of a cold front.

- Mostly dry conditions with temperatures dipping below average during the mid to late week period.

- Next chance at precipitation Saturday night into Sunday.

DTW THRESHOLD PROBABILITIES

* Low in thunderstorms this morning and afternoon.

* Low for westerly crosswinds this afternoon.

PREV DISCUSSION

Issued at 335 AM EDT Tue Jul 21 2026

DISCUSSION...

A cluster of thunderstorms will continue to sweep across north/central Lower Michigan along the lead edge of an instability gradient and warm front early this morning. There is a respectable warm layer aloft over southeast Michigan per 00Z DTX RAOB last evening with mesoanalysis showing very limited surface instability. This should help limit overall convective potential as the cluster of thunderstorms move through. Mid-level lapse rates with 20-30 knots of effective bulk shear will still allow for any stronger updrafts to pose an isolated damaging wind threat as this lead wave works through the Saginaw Valley and Thumb. The arrival of deeper moisture will also support brief heavy downpours.

Evening suite of hi-res models are struggling to capture the lack of convection with southern extent as several have much higher coverage that reaches southern areas of southeast Michigan. Thus, the isolated severe threat looks confined along and north of I-69 through the remainder of the early morning hours. There is a secondary weak wave that may move out of northern IL that may lead to an expansion of showers across southern portions of the CWA towards 12Z, but confidence is low with how this plays out. Focus then turns to the trailing shortwave moving out of Minnesota and through Wisconsin throughout the morning. This wave and associated cold front should lead to better erosion of this mid level warm layer and provide an opportunity for an uptick in convection behind morning convection as it arrives towards the early afternoon. Increasing instability profiles with more favorable diurnal timing and better CAPE depth with bulk shear of 20+ knots allows for a chance at isolated strong to possibly severe thunderstorm development. Activity will pose mainly a damaging wind threat with a chance for small hail as well. Favored areas will include areas east of the I-75 corridor, mainly during the early to mid afternoon period. Aside from thunderstorm potential, expect westerly winds to increase throughout the morning with breezy northwest winds behind the front later today as cold and dry air advection commences.

Temperatures fall to well below average for July standards as 850 mb temperatures dip into the single digits C bringing daytime highs for Wednesday in the low to mid 70s. Comfortable humidity also expected with dewpoints to to around 50 degrees. These dry and cool conditions will carry over into Thursday. High pressure continues to limit convective potential into Friday, but southerly flow will begin to kick in to close out the work week. This will a slight moderation in the cooler airmass and help lift daytime highs up to around 80 degrees. Next prospects for precipitation look to be during the later half of the weekend when a wave moves out of the northern plains along the northern periphery of the SW CONUS ridge.

MARINE...

A cold front swept across the Great Lakes overnight, with lingering thunderstorms exiting east of the local waters this morning. Breezy westerly flow has emerged post-front with Small Craft Advisories in effect for both wind and wave concerns through Wednesday. Active pattern continues as an upper level disturbance glances overhead this afternoon, leading to additional thunderstorm chances which could produce a strong to severe storm over the waters. A second front then sweeps across the area this evening-overnight, shifting winds further to the northwest and ramping up wind gusts toward gale force for a brief period this evening (centered around 00z/8pm local). Gusts should quickly diminish with the frontal passage, thus precluding gale headlines at this time. Strong cold advection fills in behind the front which keeps breezy conditions in place through Wednesday, although drier with the arrival of high pressure that persists through late this week.

DTX WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement through Wednesday evening for MIZ049.

Lake Huron...Small Craft Advisory until 10 PM EDT Wednesday for LHZ421-441>443.

Small Craft Advisory until 4 PM EDT Wednesday for LHZ422.

Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT this evening for LEZ444.