275
FXUS63 KGRR 220658
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
258 AM EDT Sat Aug 22 2026

.KEY MESSAGES...

- Scattered Showers/Storms Press East Today

- Cooler and Breezy Sunday into Monday

- Midweek Rain Chances

&&

.DISCUSSION...
Issued at 258 AM EDT Sat Aug 22 2026

- Scattered Showers/Storms Press East Today

Prefrontal scattered showers and thunderstorms have developed in a
weakly sheared environment with MUCAPE values around 1000-1500
J/kg. This activity was best depicted by the 00z HRRR, though
several of the CAMs have had at least somewhat of a clue. While
many areas will completely avoid rain into the morning hours,
small pockets of 0.25" or more are possible mainly near and west
of US 131 where elevated instability is present. As the cold front
moves into the region in the 12z-15z time frame, rain chances will
press east with the front, and by 18z much if not all of the
showers/storms will push east of US 127. One exception may be a
few showers and storms that develop along the lakeshore after 21z
underneath a post-frontal vort lobe that swings through the U.P.
and WI, helping generate some precip over Lake Michigan given a
somewhat more unstable boundary layer. NBM is not really picking
up on this, but we may need to introduce POPs along the lakeshore
for the evening hours depending on upstream convective trends this
afternoon.

- Cooler and Breezy Sunday into Monday

Anomalous upper troughing, as indicated by the 00z ECWMF`s 500mb
height anomalies of ~3 standard deviations below normal across
the Great Lakes on Sunday, will assuredly cause cold air advection
in the lower levels and also enhance surface wind speeds Sunday
into Monday. Normal highs are in the low 80s, but we should max
out around 70 to the low 70s on Sunday and maybe a touch warmer
Monday. Wind gusts of 25 mph or greater are likely on Sunday, with
gusts of 20 mph or greater likely on Monday.

- Midweek Rain Chances

Upper troughing returns in the Wednesday to Thursday time frame,
with some weak upper jet divergence moving in. At the surface, a
cold front is shown by model guidance to move through the Great
Lakes. This system will not be tapping Gulf moisture, and the low
and mid level winds don`t look strong at this time. Still, there
will be an opportunity for some scattered showers and storms with
timing better pinned down as we get closer to this event.


&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 140 AM EDT Sat Aug 22 2026

As well depicted by the 00z HRRR, a batch of showers and a few
thunderstorms developed over Lake Michigan between 04z-05z and
were moving east. With weak shear, this activity will tend to wax
and wane through 10z or so, with some periods of IFR most probable
at GRR. Given cell movement, felt most confident to put TEMPO in
for -TSRA at GRR through 10z. With a cold front passing through
around 12z, expect a wind shift to occur with SW winds turning NW
through mid morning. Rain chances decrease from west to east, with
LAN/JXN the last to clear out potentially as late as 18z or so.

&&

.MARINE...
Issued at 258 AM EDT Sat Aug 22 2026

As a cold front moves through the region today, winds will turn NW
after 12z with a good fetch over the lake. With cold air advection
taking place today into Sunday, this will be a setup for hazardous
winds and waves to small craft and also hazardous swim conditions
especially south of Pentwater today and then all areas on Sunday.
Small Craft Advisories and Beach Hazards Statements are in effect
for all marine areas starting 8am today and lasting through Sunday
evening. The north sides of piers will be especially dangerous,
and piers may be swamped by waves. Sunday will likely feature the
highest wave activity with 4 to 6 feet expected.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from 8 AM EDT this morning through
     Sunday evening for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from 8 AM this morning to 11 PM EDT Sunday
     for LMZ844>849.

&&

$$

DISCUSSION...Hoving
AVIATION...Hoving
MARINE...Hoving