textproduct: Grand Rapids

KEY MESSAGES

- Isolated Showers and Storms Today South of I-96

- Heat Wave Possible Mon-Wed

DISCUSSION

Issued at 343 AM EDT Fri Jul 10 2026

- Isolated Showers and Storms Today South of I-96

Relatively moist air lingering in southern Michigan along with MLCAPE projected around 1000 J/kg south of Holland-Lansing, limited convective inhibition, and weak surface convergence, means that isolated to scattered showers or thunderstorms are possible today. Low level wind shear will likely be minimal and 0-6 km shear no more than 20 knots. Any storms will primarily be an isolated microburst/wind threat, though unlikely to be severe. With 0-3 km CAPE over 100 J/kg, LCLs around 1 km, and perhaps zones of weak surface vorticity along converging wind fields, any storm cells that do track along surface vorticity zones could make an attempt at landspouts like yesterday.

- Heat Wave Possible Mon-Wed

Significant heat wave developing this weekend from the Intermountain West to Northern High Plains, with the forecast offices in Salt Lake, Riverton, and Billings mentioning all-time record highs being challenged. The associated 500 mb high will migrate toward the Dakotas with 600 dekameter heights on Monday. A plume of very warm 850 mb air will advect toward Michigan from the northwest, with the ECMWF favoring 21-23 C temperatures at that level over us Mon-Tue, possibly into Wed.

The EC-ENS and GEPS have been on board for a few days now with high temperatures in the 90s (away from Lake Michigan) Monday through Wednesday. A growing number of GEFS members are also pushing highs above 90 on Tue. Dew points in the lower to mid 60s (instead of the 70s like the heat wave last week) should keep the heat index relatively in check, though a heat index in the 90s to near 100 for a few days still carries risk of heat illness. On but especially after Wed, the spread in solutions grows depending on the magnitude of the eastern Canadian trough, which makes a big difference in how much and how quickly we cool back down later in the week.

AVIATION /18Z TAFS THROUGH 18Z SATURDAY/

Issued at 124 PM EDT Fri Jul 10 2026

MVFR cigs are scattering out, with the last terminal (BTL) reaching VFR around 18z. VFR conditions then continue through the rest of the TAF period with one caveat. There is a 30% chance of thunderstorms around the I-94 terminals through early evening, and if one impacts a terminal a brief period of MVFR and lower conditions is likely. Northerly winds to 3-8 knots today become northeasterly for Saturday.

MARINE

Issued at 343 AM EDT Fri Jul 10 2026

Winds from the northeast this morning become northwest and strengthen to 15 to 20 knots this afternoon with the additive effects of a ridge of higher pressure over Wisconsin and the daytime lake breeze. A moderate swim risk is likely to develop by mid-late afternoon between Whitehall and South Haven, especially affecting beaches north of north piers. Waves may build 2 to 4 feet, and some gusts may approach 22 knots per the HRRR. This setup appears similar to Monday, which was another close call moderate-to-high swim risk day.

GRR WATCHES/WARNINGS/ADVISORIES

MI...None. MARINE...None.