textproduct: Detroit/Pontiac

KEY MESSAGES

- Dry and cool through Friday.

- Rain returns by Friday night and continues into Saturday morning.

- A little milder this weekend, with chances for thunderstorms Saturday and Sunday.

DTW THRESHOLD PROBABILITIES

* None

PREV DISCUSSION

Issued at 407 AM EDT Thu May 21 2026

DISCUSSION...

Broad isentropic descent around the periphery of a sprawling anticyclone over the northern Great Lakes maintains dry and stable conditions today into tomorrow. The surface high over Lake Superior slowly migrates east over the next 36 hours, maintaining light northeast wind that veers to easterly on Friday. Cool air within this pattern holds temperatures on the lower side of average, with highs in the 60s for most of the area and 50s near the lakeshores. A good amount of sun this morning gives way to high clouds arriving this afternoon within the upper jet entrance region. Lows tonight settle into the 40s with the northeast gradient wind persisting.

A convective shortwave over central TX this morning ejects northeast today, carrying a humid air mass through the Tennessee and Ohio Valleys that reaches the southern Great Lakes late Friday. Initially dry mid and low levels are favored to hold rain chances at bay until early evening or after sunset, then rain will spread in from the south as isentropic ascent on the north flank of the wave gains traction. The inbound air mass is characterized by 850mb dew point of 10 to 12C and PWAT between 1.25 and 1.50", so a round of soaking rain is likely Friday night through early Saturday. Lapse rates through the column during this period are weak and instability will be minimal, so thunderstorms are not currently anticipated.

The steadiest rain is expected to move out by midday Saturday, then additional scattered to numerous showers are likely into Saturday afternoon. There is still noteworthy variance among ensemble solutions regarding surface low strength and track on Saturday. More progressive solutions tend to bring in drier air and an earlier end to precip, while slower solutions keep a higher coverage of showers and some thunderstorms around even into the evening. Will maintain 40-70% PoPs with respect for the mid-level wave tracking overhead, but this period may be subject to revisions.

Another upper wave passes through on Sunday bringing another window for showers and thunderstorms. A warming trend follows next week with good consensus among grand ensemble 500mb progs in depicting an omega blocking ridge setting up over Ontario by mid to late week. Governing subsident environment during this period favors mainly dry conditions, but placement near the edge of the cap brings low end potential for occasional showers and storms.

MARINE...

High pressure centered over the northern Great Lakes will hold through tonight. Winds will be out of northeast today and largely below 20 knots. The exception will be Lake Erie where fetch down the long axis of the lake will locally increase winds and waves in the western basin, and a long duration Small Craft Advisory has been issued. The next low pressure system will lift into the region from the south late Friday into Saturday which will bring the next potential for showers and thunderstorms. Winds continue out of the northeast on Friday but will increase as the gradient tightens between the existing high and approaching low. Gusts may reach 30 knots through that period.

HYDROLOGY...

A round of steady soaking rainfall is forecast to spread across southeast MI from south to north Friday evening into Saturday morning as low pressure lifts in from the Mid Mississippi Valley. Additional showers and some thunderstorms are possible Saturday afternoon but carry less certainty at this time. Forecast rainfall totals range generally between a half inch and 1 inch during this event. Overall dry conditions for much of the area over the past 30 days suggests the potential for flooding is low.

DTX WATCHES/WARNINGS/ADVISORIES

MI...None. Lake Huron...None. Lake St Clair...None. Michigan waters of Lake Erie...Small Craft Advisory from 4 PM this afternoon to 10 AM EDT Saturday for LEZ444.