textproduct: Detroit/Pontiac

KEY MESSAGES

- Scattered showers and thunderstorms move into the Tri Cities today, expanding across the rest of SE Michigan tonight.

- An unsettled pattern continues Thursday into the weekend with periods of showers and thunderstorms likely.

DISCUSSION

A cold front is draped from the Straits down to the Milwaukee vicinity this morning, orphaned off by parent low pressure quickly racing across northern Quebec. Forward momentum carries the front slowly eastward today, with a few nudges from several weak shortwaves in the mid-level flow. One of these is passing across Lake Michigan this morning, tied to jet entrance region ascent aloft. Shower production has increased along this segment of the front - this activity mainly targets northern Lower MI this morning but also offers a 20-40% chance for some showers in the Saginaw Valley before noon.

Thickness advection via southwest flow and lots of insolation bring an uptick in warmth for most of SE MI compared to the past few days. Mid to upper 80s will be common for a high temp. Meanwhile, higher coverage of cloud closer the front should limit temps to the lower 80s in the Saginaw Valley. There will be a lull in upper forcing during the day and low-level moisture looks to hold close to the surface front just upstream, so confidence is relatively low on development of additional showers in the CWA. Afternoon convection that develops in some CAM solutions appear to be tied to a differential heating boundary in the Saginaw Valley/I-69 corridor - this may provide enough of a trigger absent of larger scale forcing aloft. HREF and REFS ensemble mean SBCAPE and bulk wind shear on the order of 500 J/kg and 25 kt respectively would support disorganized clusters of thunderstorms with little potential for severe weather. Otherwise, lack of low-level moisture and forcing should help keep much of the area dry and warm today.

Better signal for ascent works in late this evening and overnight as a jet streak rounds the base of the longwave trough upstream, with its entrance region passing overhead coincident with PVA and height falls between 00z and 09z. The highest PoPs (50-60%) set up generally north and west of Metro Detroit overnight. Some showers/storms may produce localized heavy rainfall. The front advances farther into SE MI daytime Thursday, with more favorable diurnal timing and another mid-level disturbance supporting a 50-60% PoP mainly south and east of a line from Owosso to Sandusky. Similar instability and wind shear progs will bring potential for isolated to scattered thunderstorms but limit chances for severe weather. The front progresses south of the area Thursday night with weak high pressure offering a window for drier conditions. The front is then shown to drift back northward on Friday with another window for scattered showers and storms.

Unsettled conditions look likely to continue into the weekend and possibly beyond as high pressure settles over the Four Corners and low pressure over Hudson Bay maintains an active northwest flow pattern into the Great Lakes. Still time to gather details on more specific windows of higher probability for precip, but this upper pattern generally holds in place into early and possibly mid next week.

MARINE

A low pressure system slows over Hudson Bay today, with its extended attendant cold front approaching the central Great Lakes from the west. This provides the first opportunity for showers and a few thunderstorms this week, as the boundary likely stalls over Lake Huron tonight. Several disturbances are then expected to ripple over the boundary, preserving rain/storm chances through Thursday. The front should resume forward progress on Friday with additional chances for convection for the southern waterways. Winds are expected to remain below headline criteria through the rest of the week. Drier weather may briefly return for parts of Friday and/or Saturday, but the front will stall out again in the vicinity, keeping low chances for thunder through the weekend.

PREV DISCUSSION

Issued at 1140 PM EDT Tue Aug 4 2026

AVIATION...

High pressure continues to influence the region through tonight maintaining VFR skies and light winds. Approaching slow-moving cold front results in increasing mid and eventual low cloud over the course of Wednesday afternoon-evening from north to south. Shower and storm chances within the current forecast period are confined towards the Saginaw Valley, given the frontal orientation, with current best chances for storms at MBS/FNT looking to occur late evening/overnight.

D21/DTW Convection...No thunderstorms expected for the forecast period at DTW, convective potential looks to be confined from FNT- north.

DTW THRESHOLD PROBABILITIES...

* None

DTX WATCHES/WARNINGS/ADVISORIES

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