327 FXUS63 KGRR 302345 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 745 PM EDT Tue Jun 30 2026 .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 /00Z TAFS THROUGH 00Z THURSDAY/... Issued at 745 PM EDT Tue Jun 30 2026 We estimate a 90 percent chance of all terminals remaining VFR through at least 06Z tonight. A possible exception would be MKG, which has a low (20 percent) chance of experiencing thunderstorms, per AWC CCFP guidance, which may be influenced by some CAM solutions (such as the NAMNest and the WRF-ARW) that bring thunderstorms into the northwest forecast area. For now we are sticking more with the HiRes-FV3, which has been performing a bit better with the "ring of fire" convection lately, and for tonight keeps convection well to the north. Wind gusts have mostly diminished, but MKG may see renewed gusts later tonight off Lake MI. Went with a scattered layer of stratocumulus at 3000 ft tonight at most of the terminals and it`s possible that this layer becomes broken in spots going into early Wednesday morning. && .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...Beach Hazards Statement until 8 PM EDT this evening for MIZ037- 043-050-056. Extreme Heat Warning until 8 PM EDT Thursday for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. Air Quality Alert until midnight EDT tonight for MIZ050-056-057- 064-071. MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ846>849. && $$ DISCUSSION...CAS AVIATION...TJT MARINE...CAS

NWS GRR Office Area Forecast Discussion