Marine Weather and Tide Forecast for Grosse Pointe, MI

AVIATION

Warming of the 5-8 kft AGL layer is resulting in an increasingly stable environment despite heat and humidity building in at the surface. Beneath the veil of high cirrus, a few boundary layer clouds can be expected through the afternoon with strengthening southwest wind gusting upward of 25 to 30 kt. A 40 to 50 kt jet core will pass overhead within the 2-4 kft AGL layer overnight, leading to possible LLWS concerns. However neutral stability near the surface should keep a degree of mixing within the boundary layer which will mitigate a stronger shear layer developing. Less gusty WSW wind on Sunday with prevailing VFR.

For DTW/D21 Convection...No thunderstorms are forecast.

THRESHOLD PROBABILITIES...

* None.

PREV DISCUSSION
Issued at 1000 AM EDT Sat Jun 21 2025

UPDATE...

Intense rainfall and hail with storms which tracked through the middle tier of the CWA, with echo tops reaching 50,000+ feet. 12z DTX sounding came in with a PW value of 1.82 inches, short of the daily record. Even so, no surprise rainfall totals exceeded 2 inches across parts of Genesee/Lapeer counties. Officially, Flint Bishop airport reported 1.53 inches, also short of the daily record (1.8" in 2006).

Waiting on the storms to clear by noon and will send out clean zones, as we should be capped with the deep southwest flow pumping in the heat. Max temps rising in the lower 90s late this afternoon still looks to be track based on current upstream trends. As the boundary layer increases during the day, still looks like wind gusts in the 35-45 mph range, with Saginaw Valley seeing the highest gusts. Isolated and short window of the stronger winds, no wind advisory planned.

Will deal with the heat headlines and potential decisions with the afternoon package.

PREV DISCUSSION...
Issued at 334 AM EDT Sat Jun 21 2025

DISCUSSION...

Heat will be the main story for the forecast but we'll first talk about the early morning thunderstorm chances for today. We still reside on the east side of the ridge axis with the strong 850mb low level jet >65 knots back over MN causing intense overnight convection which will drift east and north through the U.P. and/or Lake Superior the rest of tonight through morning. Farther south over southern MI, we'll be watching for an elevated warm frontal boundary and ribbon of high 850-700mb theta e to extend eastward into SE MI and then lift northward through morning (generally 09- 15Z) as the ridge axis passes and warm front gets forced north.
Models have shifted northward with the MCS track, thus we should be dealing with more of the frontal forcing and less of the MCS potential. We reside on the far eastern periphery of the low level jet, but should get a brief increase locally to around to around 30- 35 knots as the ridge nudges east. No shortage of elevated instability to work with as models have been pretty consistent with MUCAPE around 1500-2000 J/kg (RAP wants to bring in 3000 J/kg) over the region with 30-40 knots of shear. We remain largely in a Marginal Risk of severe weather per SPC which seems warranted given the parameter space. Also ample moisture to work with as PWATs peak around 1.8 inches with dewpoints in the 70s so heavy rain will be a potential with any storm that develops. With most of the convection being elevated above a stable layer around 7kft deep, looking at a wind/hail threat with any stronger storms.

Strong warm air advection takes place in the wake of the front gusty southwest winds helping to advect warm airmass into the region while the ridge folds over helping to warm the entire airmass. 850mb temps will reaching 20C by 00Z this evening and with temps starting off around 70 this morning, shouldn't have a hard time making a run at 90 this afternoon. Dewpoints in the 70s will result in heat indices around 100F thus we have a Heat Advisory in effect starting this afternoon. As mentioned for several days now, this heat wave will continue through the early part of the week as the ridge of high pressure strengthens over the east coast with 500mb heights up to 598 DAM. Near record high temps will be possible Sunday and Monday with highs in the mid to upper 90s. Little relief with overnight temps holding in the 70s will lead to compounding effect through the stretch with little opportunity for relief from the heat. Extreme Heat Watch remains in effect Sunday through Tuesday at this time.

Mid to late week the ridge weakens slightly and retrogrades west while the easterly flow gets more energetic across Canada which will flatten the ridge. The ridge will still be strong enough to slow the advancement of a southward drifting frontal boundary somewhat, but question will be where does this set up which will dictate how far south the precipitation will make it and how much of the CWA can keep the heat around. Pretty good chance of a portion of the area making another run at 90F but storm chances also return during this time which leads to lower confidence.

MARINE...

A warm and unstable airmass has started building into the Great Lakes region this morning, triggering a linear complex of elevated thunderstorms that will linger through mid-morning. The primary hazards with this complex are frequent lightning and torrential downpours, although isolated gusts of 34+ knots and large hail cannot be ruled out. Rain chances diminish by this afternoon as winds shift to the southwest, strengthening toward 15 to 20 knots with gusts of 25-30 knots. These conditions have prompted Small Craft Advisories for the Lake Huron nearshore zones, with highest winds/waves expected close to the shoreline and over Saginaw Bay.
The cooler open waters will be more stable meaning momentum transfer will not be as efficient, while shorter duration and lower magnitude preclude Lake Saint Clair and Lake Erie from the advisory. Southwest flow holds firmly in place through the weekend into early next week, with sustained winds of 15-20 knots keeping waves just below advisory thresholds (2 to 4 feet) and gusts around 20-25 knots.

HYDROLOGY...

A warm front lifting through Lower Michigan early this morning will bring the potential to support showers and thunderstorms.
Instability and moisture will be on the increase, with PW values topping out around 2 inches. Thus, any strong thunderstorms that develop will produce torrential downpours. Uncertainty exists with the areal coverage of the activity, with main window looking to be 5 - 11 AM this morning. There is the potential for local rainfall totals to exceed 2 inches in a short period of time, which would lead to urban and low lying flooding. Recent rainfall over the past couple of days has made many areas more susceptible to flooding.

CLIMATE...

The record highs for Sunday, June 22nd.

Detroit: 98 Degrees (Set in 1988)
Flint: 96 Degrees (Set in 1923)
Saginaw: 94 Degrees (Set in 1966)

The record high minimums for June 22nd.

Detroit: 73 Degrees (Set in 1988)
Flint: 71 Degrees (Set in 1988)
Saginaw: 69 Degrees (Set in 2024)

The record highs for Monday, June 23rd.

Detroit: 95 Degrees (Set in 1923)
Flint: 98 Degrees (Set in 1923)
Saginaw: 96 Degrees (Set in 1923)

The record high minimums for June 23rd.

Detroit: 74 Degrees (Set in 1923)
Flint: 71 Degrees (Set in 2013)
Saginaw: 72 Degrees (Set in 1975)

The record highs for Tuesday, June 24th.

Detroit: 97 Degrees (Set in 1952)
Flint: 95 Degrees (Set in 1934)
Saginaw: 96 Degrees (Set in 1938)

The record high minimums for June 24th.

Detroit: 74 Degrees (Set in 1923)
Flint: 73 Degrees (Set in 1997)
Saginaw: 73 Degrees (Set in 1997)

DTX WATCHES/WARNINGS/ADVISORIES
MI...Heat Advisory until 8 AM EDT Sunday for MIZ047>049-053>055-060>063- 068>070-075-076-082-083.

Lake Huron...Small Craft Advisory until 4 AM EDT Sunday for LHZ421-422.

Small Craft Advisory until 10 PM EDT this evening for LHZ441>443.

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