719
FXUS63 KGRR 131858
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
258 PM EDT Sun Jul 13 2025

.KEY MESSAGES...

- Heat Builds into Tuesday

- Chances for Showers and Storms Midweek

- Another Chance for Rain Potentially Next Weekend

&&

.DISCUSSION...
Issued at 221 PM EDT Sun Jul 13 2025

- Heat Builds into Tuesday

Quiet weather will prevail from tonight into the day on Tuesday as
high pressure drifts through the Great Lakes region. BUFKIT
overviews show very little moisture in the profile. Some high
clouds moving through the region today will shift southeast
tonight and there will be some scattered cumulus development
tomorrow, but that is it. No prospects for rain in the next 48
hours.

Heat will build from today through Tuesday with high temperatures
creeping up from the middle 80s today to around 90 on Tuesday.
There is not a big increase in 850mb temperatures, but they are
already warm. We actually stay between +16C and +18C through
Thursday. So, upper 80s to around 90 the next couple of days. Mid
week temperatures will be affected by convective clouds and
precipitation.

- Chances for Showers and Storms Midweek

We could see some showers and storm leak into the area from the
west Tuesday night, but the better bet is we remain dry Tuesday
night as well. The focus is really on a weak boundary which will
sag through the area in the Wednesday through Thursday night time
frame.

The best chances for showers and storms look to be both Wednesday
afternoon and evening and again Thursday afternoon and evening.
Obvious reason there are higher chances during that time is due
to being at the diurnal peak, but also due to the fact that two
separate shortwaves are forecast to be moving through the area at
those times. We have likely chances for showers/storms (60 pct)
during the afternoon/evening both days. Each day has some
semblance of a low level jet with Wednesday having stronger
winds. Each day has MUCAPE values around 2,000 j/kg potentially.
In terms of deep layer shear it looks to be 20-30 knots so not
overly strong but bad either. Potential for some stronger storms
both days for sure, so we will be watching this time frame going
forward.

Precipitable water values eclipse 2.00 inches both days so locally
heavy rain is certainly possible.

- Another Chance for Rain Potentially Next Weekend

There is model disparity with regard to a system next weekend. The
ECMWF has a low moving through the Great Lakes Saturday night into
Sunday, while the GFS is now beginning to trend some precip in as
well. As we move forward the expectation is that both will likely
have a system next weekend. Plenty of time to watch how the
pattern evolves.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 137 PM EDT Sun Jul 13 2025

Diurnal cu will dissipate as sunset nears leaving broken high
clouds overnight and Monday. Wind will remain light from the west.

&&

.MARINE...
Issued at 137 PM EDT Sun Jul 13 2025

A weak pressure gradient will continue through Tuesday, after
which increasing southwest flow will begin to push waves higher
from north to south. Swim risk at the lakeshore will remain low
through Tuesday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Air Quality Alert until midnight EDT Monday night for MIZ037>040-
     043>046-050>052-056>059-064>067-071>074.
MARINE...None.

&&

$$

DISCUSSION...Duke
AVIATION...04
MARINE...04