845
FXUS63 KGRR 212337
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
737 PM EDT Mon Jul 21 2025

.KEY MESSAGES...

- Building heat and humidity

- Showers/storm late week

&&

.DISCUSSION...
Issued at 300 PM EDT Mon Jul 21 2025

- Building heat and humidity

Another comfortable night is in store with clear skies and lows in
the 50s tonight. Then, the heat begins to build.

High pressure near James Bay is producing a light northeast wind
flow today, However, as the high drifts east tomorrow, a southerly
flow will develop at the surface. Aloft, a ridge will build as
Wednesday approaches and the heat pump will be in full gear.
Dewpoints will climb from today`s 50s to lower 70s Wednesday and
lower to mid 70s Thursday. Dewpoints will hover around 70 through
the weekend.

Highs tomorrow will climb into the lower to mid 80s. H8 temps will
climb to 22c by Wednesday afternoon resulting in surface highs in
the lower 90s Wednesday and lower to mid 90s Thursday. Apparent
temperatures will be around 100 Wednesday and 100-105 Thursday.
We`ll likely need a heat advisory for those days.

Temperatures won`t be much cooler over the weekend. Highs will
remain around 90, but dewpoints will back off to the mid to upper
60s; still humid, but not quite as oppressive.

- Showers/storm late week

The next chance of rain arrives Thursday night. A series of short
waves will flatten the ridge and push a weak cold front south
across the cwa. This frontal boundary is progd to stall over
northern IN. There`s a 60-70 percent chance of showers/storms
Thursday night/Friday over the cwa as the boundary moves south,
then a 30 percent chance of showers/storms Friday night/Saturday
over the southern cwa as the boundary stalls.

Precipitable water values aoa 2 inches will increase the chances
for heavy rainfall where thunderstorms develop Thursday and Friday.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 737 PM EDT Mon Jul 21 2025

VFR is expected with winds generally less than 10 knots from the
east, becoming southeast Tuesday morning. A few daytime cumulus
with bases around 5,000 ft are dissipating. Scattered clouds with
12,000 ft and 25,000 ft bases tonight. A few clouds around 4,000
ft possible during the day Tue.

&&

.MARINE...
Issued at 140 PM EDT Mon Jul 21 2025

North-northwest winds around 10 knots today will become east
tonight with waves around 1 foot. South winds on Tuesday 10-15
knots may build up some 2-3 ft waves north of Whitehall. 15-20
knot winds from the south on Wed may create at least moderate
swim risk and 2 to 4 ft waves north of Grand Haven. There is a
chance of small craft advisory conditions and high swim risk on
Wed, but a couple previous occasions this summer of hot and humid
days with breezy south winds did not result in the 3 to 5 ft
waves that were expected.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...04
AVIATION...CAS
MARINE...CAS