846
FXUS63 KGRR 301920
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
320 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 /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 136 PM EDT Tue Jun 30 2026
Areas of MVFR ceilings affecting some of the terminals are expected
to change into a scattered layer above 3000 ft this afternoon. It
is interesting to note that multiple cloud layers in the 2000-3000
ft range have been reported at some of the terminals having
automated ASOS observations. This suggests that stratocumulus is
indeed breaking up because this process can often trick the small
diameter, upward pointing cloud sensors as well as the averaging
algorithms associated with the ASOS platforms.
Other than that, have tried to capture the gusty nature of winds
with gusts expected to subside around or shortly after 00Z.
&&
.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
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