textproduct: Detroit/Pontiac

KEY MESSAGES

- Scattered to numerous showers and thunderstorms this morning become more widespread this afternoon.

- There is a Marginal/Isolated risk of strong/severe thunderstorms this afternoon.

- Breezy and cooler conditions arrive Sunday with scattered showers through Sunday night.

- A stray shower in the morning, otherwise dry Monday with slightly below normal temperatures.

DTW THRESHOLD PROBABILITIES

* High low for thunderstorms after 18z today.

* Low for ceilings at or below 5000 ft this morning. Moderate in the afternoon. High tonight.

PREV DISCUSSION

Issued at 353 AM EDT Sat Aug 22 2026

DISCUSSION...

An active period of showers and thunderstorms continues in a couple of phases as Straits low pressure pulls a cold front through Lower Mi today. Clusters of showers and thunderstorms that are ongoing leading up to sunrise are within the low to mid level moisture axis ahead of the cold front. This is where model soundings indicate a deep layer of elevated instability, but with minimal CAPE density shown in both the soundings and implied by plan view depictions of 850 mb LI around -2 C and sub 7 C/km 700-500 mb lapse rate. This elevated convection merges with scattered hybrid surface based activity of similar intensity during the morning within and between a prefrontal surface trough and the inbound cold front.

The early day activity adds some doubt about verification of model peak instability as the cold front sweeps through SE Mi this afternoon. However, HREF and REFS members all handle the ongoing activity reasonably well and still suggest a respectable recovery in time for the front to support a storm flare-up while overhead and before it exits into Ontario toward early evening. There is otherwise no big change in the CAPE/shear environment as HREF mean surface based CAPE holds below 1500 J/kg with bulk shear around 25 knots, good enough for multicell clusters capable of peak gusts approaching severe intensity as the primary hazard in the strongest storms. The Marginal Risk remains in place to highlight this potential in SE Mi with a Slight Risk now just east of the border until the front exits early this evening.

Scattered showers trail the front, mainly during the evening, as the 500 mb trough digs toward the eastern Great Lakes, but also as moderate cold advection gains traction overnight. Increasing NW flow occurs across Lower Mi around the west flank of surface low pressure deepening on the Ontario/Quebec border as the 500 mb trough deepens and closes off early Sunday. Model agreement maintains the trend on solutions offering a larger mid level circulation closing off closer to Lower Mi during the day. There is also a well-defined reinforcing vorticity maximum holding consistency in model solutions as it digs in from the NW and moves overhead during the afternoon. Guidance probabilities for rain appear underdone in this environment as scattered to numerous coverage is favored, especially Sunday afternoon and evening with a boost from daytime instability.

The low level thermal trough is firmly in place over the western Great Lakes by Monday morning with low temperatures in the upper 40s still within reach outside of the larger metro areas. Deterministic and ensemble model guidance continue to project single digit 850 mb temperatures to start the day which rebound quickly as the mid/upper level low shifts eastward. A stray shower also remains in play, especially toward the Thumb region, during the morning until confluent NW flow develops to help ensure dry weather for the afternoon and Monday night. Slightly below normal highs in the upper 70s are reachable as the thermal trough shifts eastward.

Weak surface high pressure is supported by a mid/upper level short wave ridge Monday night and Tuesday. Dry weather and a few degrees of warming occur through mid week within the slowly progressive large scale flow. High temperatures return to the lower 80s during mid week while the next chance of rain is carried in by the current Pac NW system. Extended range global models project it arrives in the Great Lakes by Wednesday.

MARINE...

A cold front will progress across the Great Lakes while expanding shower and thunderstorm chances today. Any stronger storm development will be capable of producing wind gusts aoa 34 knots and/or small hail. Winds veer to the northwest in the wake of the passing front and will increase intensity and remain elevated through Sunday as cooler air is ushered in. Wind gusts will likely range around 25 to 30 knots through this weekend. The switch in wind direction from the northwest will quickly build wave heights in and around the Thumb and Small Craft Advisories are in effect beginning tonight. High pressure builds back in Monday and Tuesday which will bring lighter winds to the area.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...Small Craft Advisory from 8 PM this evening to 10 AM EDT Monday for LHZ421-441.

Small Craft Advisory from 8 PM this evening to 4 AM EDT Monday for LHZ422.

Small Craft Advisory from midnight tonight to 10 AM EDT Monday for LHZ442-443.

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