668
FXUS63 KGRR 192258
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
658 PM EDT Tue Aug 19 2025

.KEY MESSAGES...

- Seasonable temps, less humidity, and mainly dry through Fri

- Next widespread chance of rain Friday night-Saturday

- Pattern change with much cooler conditions Sunday and beyond

&&

.DISCUSSION...
Issued at 310 PM EDT Tue Aug 19 2025

- Seasonable temps, less humidity, and mainly dry through Fri

The last of the organized rain chances with this current system are
winding down quickly outside of a lingering sprinkle through the
rest of this afternoon. The only real showers left area SE of the
cold front which is east of I-69 as of 19z/3 pm EDT. Extensive cloud
cover and a worked over atmosphere from the showers/storms that
moved through early this morning has really limited instability to
work with.

Cloud cover upstream over Wisconsin is optimistic at first look for
the area to clear out tonight. Some of that may happen, but a flow
from the NE will likely bring moisture inland from Lake Huron. This,
combined with a residual moist boundary layer will lead to a
heightened chance of low clouds and/or some fog. We will finally see
some good sold clearing then after Wednesday morning, with moisture
mixing out in the form of cumulus clouds.

High pressure will then take control of the weather over the area
through Friday. Subsidence and drier air will even limit the cumulus
development Thursday and Friday. Temperatures look like they will
mostly range in the upper 70s to lower 80s through Friday as 850 mb
temps stay in the mid teens C during this time.

- Next widespread chance of rain Fri night-Sat

The upper ridge bringing the quiet weather to the area through
Friday will be flattened a bit by an upper low that is currently
over British Columbia. The leading edge of this system will arrive
in the form of a cold front Friday night from the NW.

Rain chances are not too exciting around here with the front Friday
night and Saturday. This is evident by Ensemble Mean amounts of
rainfall generally less than 0.2 inches for most of our area with
this front. A significant factor in the limited rain potential with
this is that there is really no moisture for it to work with. The
return flow ahead of the front is sourced from the Central Plains.
The best chance of pcpn will be from limited instability with the
front. Even that is quite poor as the front will be coming through
during the coolest part of the day.

- Pattern change with much cooler conditions Sun and beyond

Rain chances with the front look to end by late Saturday afternoon
with the passage of the front by that time. That does not mean the
end of the rain chances however.

This upper low ends up getting almost stuck over the Upper Midwest
and Upper Great Lakes, and ends up developing a bit stronger than
previously expected. This happens as it will be held up by Hurricane
Erin moving over the Western Atlantic and the ridge that is just
upstream of the Hurricane. Also, an upper ridge will be
strengthening over the Western U.S., helping to trap the upper low
over our area.

The first and most noticeable change with this will be much cooler
air than the area has been used to for much of this warm summer.
Highs will be close to not making it out of the 60s early next week.
The other noticeable change will be weak short waves riding through
around the southern periphery of the low. The NBM does not print off
much in the way of precipitation. We feel this could be
underforecast. Especially that 850 mb temps will be dropping down to
the mid single digits C, and we could be looking at some lake effect
rain showers if it indeed end up that cool. Cyclonic flow aloft and
the deeper colder air will definitely help that if the colder air
aloft ends up this far south.

&&

.AVIATION /00Z TAFS THROUGH 00Z THURSDAY/...
Issued at 657 PM EDT Tue Aug 19 2025

Northeast flow behind a departing low pressure system will bring
enhanced low-level moisture overnight. For AZO, BTL, LAN, and JXN
expect cigs to fall from the present MVFR (mostly fuel-alternate
MVFR) to IFR overnight. Conditions will be mainly MVFR at GRR
where the connection to Huron`s moisture is more tenuous and may
be mostly VFR overnight with intermittent periods of MVFR at MKG
(though it wont take much to put MKG in more solid MVFR). Patchy
MVFR fog is also probable, mainly near I94 where winds are a few
knots lower. Conditions will improve from northwest to southeast
late Wednesday morning into the afternoon. How fast remains in
question, but favored more optimistic ceiling forecasts based on
observations showing drier upstream air and the fact that the
solar angle is still relatively strong. All sites should be VFR by
late evening. Expect north to northeast winds through the TAF
period, with some component of lake breeze likely at MKG in the
afternoon.

&&

.MARINE...
Issued at 310 PM EDT Tue Aug 19 2025

Have pushed up the Beach Hazards Statement and Small Craft Advisory
to begin now instead of waiting until late afternoon based on buoy
and webcam trends, particularly at Grand Haven. Sustained northwest
winds of 15-20 knots will cause waves to build into the 3 to 5 foot
range south of Muskegon through late tonight creating hazardous
conditions for beachgoers and boaters.

After a lull Wednesday morning, another increase in winds is
expected Wednesday afternoon/evening as gradient winds increase.
Northerly winds of 15-20 knots will lead to at least 2-4 foot
waves/a moderate swim risk across parts of the lake. A Beach Hazards
Statement/Small Craft Advisory may be needed for 3-5 foot waves/a
high swim risk south of Holland and up towards Big and Little Sable
Points. Given the existing headlines already in play and notable
lull between rounds will let the midnight shift make the final
determination as this event winds down.

A slacker gradient Thursday and Friday will then keep waves and
winds lower to finish the work week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 2 AM EDT Wednesday for MIZ056-064-
     071.
MARINE...Small Craft Advisory until 2 AM EDT Wednesday for LMZ844>846.

&&

$$

DISCUSSION...NJJ
AVIATION...Thomas
MARINE...Thomas