632
FXUS63 KGRR 172248
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
648 PM EDT Sun Aug 17 2025

.KEY MESSAGES...

- Next Chance for Storms Monday Night into Tuesday

- Dry and Comfortable Through the Remainder of the Week

&&

.DISCUSSION...
Issued at 258 PM EDT Sun Aug 17 2025

- Next Chance for Storms Monday Night into Tuesday

Overall the next 24 hours will be dry and comfortable. Lows
tonight drop into the 50s to low 60s with easterly winds. Our
winds gradually shift to the southeast through the day Monday with
highs in the low to mid 80s. An area of rain and storms over
Wisconsin may try to make it into areas along the lakeshore north
of Grand Haven during the afternoon. However, these showers and
storms will be moving into a more stable environment and lift will
be weakening. Therefore if the lakeshore were to see anything in
the afternoon, it would be limited to a few showers.

Our source of lift and instability will improve overnight Monday
night as the shortwave trough advects east with warm air
advection, the low level jet, and positive vorticity advection.
Precipitable water values peak at around 2 inches, therefore heavy
rainfall rates are likely with any thunderstorm. Any flooding
potential will be limited as thunderstorms shouldn`t linger over
any one area for long. Looking at the HREF 24 hour precipitation
probabilities through Tuesday morning. Isolated spots along the
lakeshore from Holland to Manistee have a 30 to 40 percent chance
of an inch or more. With thunderstorms occuring overnight limiting
MUCAPE to 500-1000 J/kg and weak shear profiles, the severe
thunderstorm risk is low.

- Dry and Comfortable Through the Remainder of the Week

Drier air moves in behind the front Tuesday with fair weather
expected through the remainder of the week as high pressure builds
in. Highs in the mid 70s to mid 80s are expected with lows in the
50s and 60s. There is a signal for a deep trough to move through
the northern Great Lakes next weekend. Cluster analysis shows
probabilities for precipitation are not high due to the dry air
mass it is associated with. It could however bring cooler air
with highs shown in the clusters on Sunday and even into next week
in the 70s.

&&

.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 645 PM EDT Sun Aug 17 2025

VFR cumulus will diminish over the next few hours with the loss
of daytime heating. Mainly cirrus as debris off of upstream
convection is expected overnight. Daytime Cu in the 4-6kft range
is then expected to develop late Monday morning and persist
through the end of the TAF period. Winds are generally northerly
to northeasterly but will become easterly to southeasterly by
Monday morning. Gusts to 20 knots are possible at MKG overnight.
There is a low, around 10 percent, chance of showers at or near
MKG after 18z Monday.

&&

.MARINE...
Issued at 645 PM EDT Sun Aug 17 2025

Have cancelled the Beach Hazards Statement and Small Craft
Advisory for Mason County/Manistee to Pentwater. Observations
suggest that while a moderate swim risk will exist through the
evening conditions will largely remain below criteria.

Have issued a Small Craft Advisory from South Haven to Pentwater
overnight. Trends in short term model guidance increase the
confidence in a few hours of 22-25 knot gusts, strongest offshore
towards the 5 mile edge of the nearshore waters. Offshore flow
will keep waves in the nearshore below hazardous levels; with
better waves in the open waters beyond 5 miles offshore.

*** Previous Discussion***

No changes to the current Small Craft Advisory/Beach Hazards
Statement. Current thinking that the north-northeast flow on the
north side of Big Sable Point/Mason County will allow for a period
of 3-5 foot waves this afternoon.

Tonight increased southeast flow is expected. Given the short fetch
and offshore direction, current thinking is that advisory level
winds and waves stay limited to the open waters beyond 5 miles from
shore. Cannot rule out isolated gusts around 22 knots between
Pentwater and South Haven within 5 miles of shore, however
confidence in meeting the duration criteria is too low to warrant
headlines. We will continue to monitor.

After this, the next day to monitor is Wednesday. Signals in several
medium range models suggest that the advancing high increase in
winds may occur along the lakeshore Wednesday afternoon.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from midnight tonight to 8 AM EDT Monday
     for LMZ845>848.

&&

$$

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