692
FXUS63 KGRR 222357
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
757 PM EDT Fri Aug 22 2025

.KEY MESSAGES...

- Limited rain chances still expected tonight and Sat

- High confidence in much cooler temps and lake effect rain Sun-Tue

- Moderating temps late week with rain chances

&&

.DISCUSSION...
Issued at 327 PM EDT Fri Aug 22 2025

- Limited rain chances still expected tonight and Sat

Setup remains quite unfavorable for a widespread rain (much less
soaking) for tonight and Saturday with the cold front moving through
the area. The timing remains the same as such that we will have
almost no diurnal instability for the front to work with, and MU
CAPEs stay generally below 1000 J/kg. This is as it passes through
most of the area between 06z tonight and 18z Saturday. Combine this
with the sfc front out ahead of the upper level wave, very limited
moisture advection/pooling along and ahead of the front really
limits the coverage. Some flare up of showers and a few storms could
occur over the far eastern portions of our forecast area as the
front exits mid-afternoon, but it will be brief and is not expected
to become strong.

- High confidence in much cooler temps and lake effect rain Sun-Tue

After the leading upper short wave moves through late Saturday
afternoon, we will see the upper cold pool and cyclonic flow aloft
start to take control over the area. This will be characterized with
rain shower coverage over the western half of the forecast
increasing through Saturday night and into Sunday and then lasting
into Tuesday.

During the heart of this lake effect potential centered around
Sunday night into Monday, lake effect rain showers will be scattered
to numerous west of U.S.-131 with a flow from the NW. There will
likely be a few diurnal showers inland, especially on Monday.

Believe it or not, thunderstorm potential looks to be high enough
Sunday night through Monday night to justify a mention of it in the
forecast. Forecast model soundings from multiple models at South
Haven show lake modified parcels having over 1,000 J/kg of CAPE, and
the updrafts extending well above the ice generation layer to
produce lightning. This is with little to no inversion resulting
from temps in the lower 70s over the water, and dew points just a
few degrees lower. We have limited the mention to the lakeshore
counties at this time.

Tuesday will see a diminishing trend as the upper trough is in the
process of moving out. Enough cold air aloft with short waves coming
in from the NW yet will keep that chance in.

- Moderating temps late week with rain chances

The latest trend in model guidance is for a break in precipitation
chances for Wednesday and now most of Thursday. The upper trough
that was forecast to drop in Thursday is now not shown to be as
strong, and a stronger trough comes in late Thursday and early
Friday.

This delay in the upper trough and rain chances will allow
temperatures to rebound a bit better with the cold air aloft east of
the area. Then rain chances will drop into the area Thursday night
and linger into Friday before the upper trough sinks south of the
area. This will reinforce the cooler air for next weekend.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 750 PM EDT Fri Aug 22 2025

VFR conditions will continue through most of the period. Cold
front will move through tomorrow and while there is a chance for
cigs and vsbys to drop to MVFR in showers it is not expected.
However, there is a slight chance for showers and storms tomorrow
afternoon. Have left Prob30 groups from 15 to 18Z considering
some questions on where the line of showers will be and adjusted
cigs. Winds will mix out with gusty winds through the day. Best
chance of showers and storms will be at MKG.


&&

.MARINE...
Issued at 327 PM EDT Fri Aug 22 2025

Wind and waves will remain below advisory levels through Saturday
morning. There is an increase chance for SCY conditions Saturday
afternoon into evening. Will wait on advisory for now for some
clarification on timing and winds are marginal Saturday at this
time. Once the winds increase behind the front expect the winds and
waves to persist Saturday evening into Monday. Waves will slowly
increase late Saturday and will become hazardous to swimmers
Saturday night through Sunday and Monday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

DISCUSSION...NJJ
AVIATION...Ceru
MARINE...Ceru