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
