textproduct: Detroit/Pontiac

KEY MESSAGES

- Showers and scattered thunderstorms will affect the area Saturday.

- Cooler and breezy conditions arrive Sunday with lingering shower chances.

DISCUSSION

Subtle mid level ridging developing over Se Mi tonight is forecast to drift across the eastern Great Lakes Friday. Associated surface high pressure and low level anticyclonic flow will hold across the eastern Great Lakes through the day Friday. The influence of this system will maintain dry weather through the next 24 to 36 hours. Much like today, there will likely be areas of diurnally driven cu and high based clouds on Friday. Light SSE flow in the boundary layer and diurnal mixing will support afternoon highs into the low 80s, which has fairly good support within the probabilistic guidance. While south flow will begin advecting a little more instability into the region Friday afternoon, model soundings indicate a strengthening mid level cap through the day which will prove a formidable limiting factor on convective initiation.

Long wave trough amplification across the Great Lakes Saturday will result in mid level height falls across Se Mi along with the passage of a surface low and cold front. A plume of deep layer moisture advection ahead of this trough late Friday/Friday night will drive precipitable water values to 1.4 to 1.6 inches. The forced ascent combined with the resident moisture and diurnal instability will support a chance of showers/thunderstorms. The model prob space is suggestive of high chances for rain Saturday, over 80 percent. Within the probabilistic guidance, median QPF is around a quarter inch, with a half inch to three quarters inch within the 90th percentile. The chances for severe weather continue to look limited (marginal risk/isolated) with SB CAPE values forecast to range from 800 to 1400 J/kg and marginal 0-6km Bulk Shear values of 20-30 knots.

Post frontal northwest flow will drive cooler air across the Great Lakes in the wake of the front; 850mb temps will drop into the single digits on Sunday. Steep low level lapse rates the cool air aloft will contribute to a healthy diurnal cu field on Sunday. This may support a few showers; the better chances will be across the thumb given the added moisture flux off Lake Huron. The cool air and daytime cloud cover will hold high temps in the 70s. Remnant northwest flow circulating around an eastern Canadian upper low will sustain seasonally cool temperatures into early next week. A northern stream short wave will provide the next chance for showers/thunderstorms during the middle of next week. At this stage in the forecast there is still ample spread among ensemble members with respect to timing and potential rainfall amounts.

MARINE

Surface high pressure lingers over Ontario rest of today and Friday, maintaining an easterly component to the overall light wind field. Winds then veer to the south Friday afternoon as a warm front lifts into the Great Lakes. Dry conditions are expected through the end of the work week, followed by increasing shower and thunderstorm chances through the day Saturday as a low and its attendant cold front sweep across Lower Michigan. This low strengthens as it moves toward New England, strengthening post-frontal northwest flow and elevating wind gusts toward 25-30 knots both Sunday and Monday. Peak gustiness is anticipated Sunday afternoon-evening when cold advection is strongest. Quieter pattern returns briefly Tuesday before the next system arrives middle of next week.

PREV DISCUSSION

Issued at 143 PM EDT Thu Aug 20 2026

AVIATION...

VFR conditions through the forecast as high pressure builds into the area. Low level moisture and elevated forcing lingering from an area of low pressure passing through Ohio last night caused some denser clouds to hold through the first part of the day south of PTK. The low is pulling away and clouds should continue to scatter this afternoon as high pressure builds over the region tonight. Patches of high clouds will pass over the region as it sheds off the warm front upstream. Winds will be light and northeasterly today but will veer easterly tonight and southerly on Friday.

D21/DTW Convection... No convection is forecast for the period.

DTW THRESHOLD PROBABILITIES...

* None.

DTX WATCHES/WARNINGS/ADVISORIES

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