550
FXUS63 KGRR 211909
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
309 PM EDT Tue Jul 21 2026

.KEY MESSAGES...

- Cooler Midweek Then Warming Up Into The Weekend

- Chance of Thunderstorms Sunday-Monday

&&

.DISCUSSION...
Issued at 309 PM EDT Tue Jul 21 2026

- Cooler Midweek Then Warming Up Into The Weekend

Scattered showers and isolated thunderstorm cells will persist
into the evening amid breezy northwest winds and cold air
advection. On Wednesday, 850 mb temperatures around 8 C will keep
highs no warmer than the mid 70s even under mostly sunny skies,
our coolest day since June 26.

The large-scale wave pattern remains rather steady-state for the
rest of the month, with an upper-level high over Colorado and the
Southwest, and troughing over the eastern Great Lakes. Shortwaves
will occasionally traverse this flow regime. Heat is expected to
build out west and then wash over Michigan this weekend. Ensembles
are nearly unanimous on the warming trend Thursday into Sunday,
then diverge from Monday onward. Temperatures are favored to climb
to around 90 on Sunday with the higher and more uncomfortable dew
points also arriving on that day.

- Chance of Thunderstorms Sunday-Monday

Along with the arrival of warmer and more humid air on Sunday,
steeper midlevel lapse rates advecting over the region will also
serve to increase instability. Another fairly robust shortwave
trough and associated surface low moving across the northern Great
Lakes will provide the next chance of thunderstorms between
Sunday and Monday. Meaningful differences do exist on the exact
track and arrival time of the low, and that means confidence in
the threat heavy rain or severe weather is relatively low for our
area at this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 132 PM EDT Tue Jul 21 2026

Scattered showers and thunderstorms this afternoon will be mostly
limited to the eastern half of Lower Michigan and the chances of
affecting LAN and JXN with MVFR or IFR ceilings or visbys will be
lower than 30 percent. Northwest winds will gust over 20 knots
this afternoon and evening before diminishing to around 10 knots
tonight.

&&

.MARINE...
Issued at 309 PM EDT Tue Jul 21 2026

Moderate to high swim risk is ongoing with 2-4 or 3-5 ft waves at
West Michigan beaches. Waves are expected to increase later this
afternoon through evening as 20-30 knot winds from the north are
channeled down the length of Lake Michigan. There could be some
gale force gusts to 35 knots near the Sable Points this evening.
Waves peak tonight at 5-10 feet then slowly subside on Wednesday,
but will remain hazardous to small craft and swimmers all day.
Upwelling of colder water along portions of the West Michigan the
shoreline is likely.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Wednesday evening for MIZ037-043-
     050-056-064-071.
MARINE...Small Craft Advisory until 11 PM EDT Wednesday for LMZ844>849.

&&

$$

DISCUSSION...CAS
AVIATION...Ostuno
MARINE...CAS