843
FXUS63 KGRR 241700
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
100 PM EDT Sun Aug 24 2025

.KEY MESSAGES...

- Lake Effect Showers and Cooler

&&

.DISCUSSION...
Issued at 335 AM EDT Sun Aug 24 2025

- Lake Effect Showers and Cooler

An upper level low will circulate over James Bay bringing a series
of shortwave troughs along with colder air aloft. Timing of the
initial shortwave moves through this afternoon bringing shower
chances across the area and triggering lake effect showers to
begin along the lakeshore as 850 mb temperatures drop. Another
shortwave Monday morning will help drive showers farther inland
again. PoPs may need to be increased for Tuesday as well with
another shortwave rotating through before the upper level low
lifts northeast.

With the lake effect showers there could be some rumbles of
thunder as there will be enough instability over the lake with
warm water temperatures around 20 to 25 degrees Celsius. 850mb
temperatures around 5 degrees Celsius will also put us within
thresholds for waterspouts to develop over Lake Michigan. If
waterspouts occur and they happen to move onshore, make sure to
keep your distance as they contain winds greater than 40 mph and
can loft loose objects.

Another front moves through Thursday which may spark off a few
showers and thunderstorms although chances are low (20 to 30
percent) at this time. Otherwise dry conditions are expected
through the remainder of the week with highs in the 60s and 70s
warming up to near 80 for next weekend. Tuesday night currently
looks to be the coldest with lows in the 40s across much of the
area with some isolated spots potentially dropping into the upper
30s.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 100 PM EDT Sun Aug 24 2025

Primary forecast concern through the period is lake effect rain
showers. Currently the best coverage is along I96 given the more
west-northwesterly flow, with lower chances towards I94. Tonight
as we go into northwesterly flow showers persist at MKG and expand
towards AZO/BTL. Predominant cigs will be VFR in the 4-6kft range
with scattered clouds in the 2-3kft range. Brief periods of MVFR
cigs/visbys are possible in any showers. At MKG, the large
air/lake temperature difference may be enough to support isolated
thunder this afternoon so have kept the PROB30 in place. Showers
move east Monday morning as a mid- level disturbance crosses the
area, though chances are too low of terminal impacts east of
AZO/BTL to warrant a TAF mention. Expect gusts to around 20 knots
both today and tomorrow in the late morning through evening hours.


&&

.MARINE...
Issued at 335 AM EDT Sun Aug 24 2025

Winds and waves will continue to be hazardous to beachgoers and
small craft within the persistent northwest winds. Gusts to 25
knots are possible mainly during the afternoon and evening with
waves building to 3 to 5 feet. In addition to winds and waves,
lake effect rain showers, thunderstorms, and waterspouts will
also be possible. Make sure to keep your distance from any
waterspout as they contain winds greater than 40 mph and can loft
loose objects. These hazards are expected to continue into Monday
before subsiding late Monday afternoon into Monday night.

The remainder of the week winds largely remain on the lighter
side with mostly dry conditions.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Monday evening for MIZ037-043-
     050-056-064-071.
MARINE...Small Craft Advisory until 8 PM EDT Monday for LMZ844>849.

&&

$$

DISCUSSION...RAH
AVIATION...Thomas
MARINE...RAH