textproduct: Grand Rapids

KEY MESSAGES

- Extreme Heat Through At Least Thursday

- Chances for Storms Next Several Days

DISCUSSION

Issued at 320 PM EDT Tue Jun 30 2026

- Extreme Heat Through At Least Thursday

Guidance continues to favor highs in the lower to mid 90s and heat indexes around 100 to 110 in most locations through Thursday. Overnight lows in the mid 70s will provide little relief to those without air conditioning, accumulating heat stress on the body. Overnight lows Wednesday morning and Thursday morning will challenge daily records for warmth. About 50 percent of ECE members have highs above 90 on Friday. High temperatures late in the week will depend on the extent and timing of thunderstorms, though generally highs in the 80s are favored through the holiday weekend.

- Chances for Storms Next Several Days

A substantial reservoir of CAPE will be present in the region through late in the week, offering potential energy for occasional thunderstorms as multiple shortwaves develop and propagate through the west-southwesterly upper-level flow pattern extending from the SW CONUS to the Great Lakes. With time, as the upper level ridge flattens a little, thunderstorms will favor southern Michigan during the latter half of the week.

For Wednesday, a threat of severe thunderstorms includes mainly US-10 and north. Thunderstorms developing today into tonight from Kansas to Nebraska may induce a wave that could continue touching off storms into Wisconsin and eventually Michigan by mid day Wednesday, especially if storms developing a cold pool and become forward-propagating. If that occurs, DCAPE well over 1000 J/kg would favor severe wind gusts. An additional threat of storms could occur late Wed night from a complex of storms that develops late in the day over southern Minnesota. Confidence is relatively low given weak lifting mechanisms and a wide variety of model solutions.

AVIATION /06Z TAFS THROUGH 06Z THURSDAY/

Issued at 208 AM EDT Wed Jul 1 2026

Broad southwest flow will continue across Southwest Lower Michigan the next 24 hours, which will likely keep the TAF sites VFR. A stationary front will remain upstream over MN, WI and the U.P. during the TAF period which should keep much of the thunderstorm activity north and west of the TAF sites. Small chances that some of this activity could work into the MKG, GRR and LAN this afternoon or evening, but feel probabilities are too low to include at this time.

We are looking for scattered to possibly broken cumulus development at times in the 5,000 to 6,000 foot range over the next 24 hours. Low ceilings and restrictions to visibility are not anticipated. Winds will be southwest at 5 to 10 knots early this morning, increasing to 10-20 knots with gusts of 20-25 knots from roughly 15z through 01z.

MARINE

Issued at 200 PM EDT Tue Jun 30 2026

Beach reports, webcams, and buoys indicate a moderate bordering on high swim risk ongoing today, with the wave spectrum generally 2 to 4 feet near and north of Holland. South-southwest winds over the lake at about 15 knots will induce some longshore currents and structural currents particularly affecting south piers.

The Port Sheldon and Ludington buoys significant wave height around 2.5 feet is less than what we have in the forecast, as the NBM winds have been a little high and the winds have been less W effective at imparting momentum onto the water in this highly stable marine air layer. Models indicate a slight uptick in winds possible this afternoon, so will hold on to this low-end Small Craft Advisory and Beach Hazards Statement until its planned expiration at 8 PM.

Another 2-4 foot wave and moderate swim risk day is expected on Wednesday. Thunderstorms on Wednesday, if they develop over Wisconsin as indicated by some models, may cross central Lake Michigan and could produce locally strong wind gusts.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Extreme Heat Warning until 8 PM EDT Thursday for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. MARINE...None.