023
FXUS63 KGRR 311900
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
300 PM EDT Sun Aug 31 2025

.KEY MESSAGES...

- Rain Likely, Chance of Thunderstorm Wed or Wed Night

- Significant Late Week Cooldown with Showers

&&

.DISCUSSION...
Issued at 300 PM EDT Sun Aug 31 2025

- Rain Likely, Chance of Thunderstorm Wed or Wed Night

Underneath weak and somewhat blocked upper-level flow, a sunny
stretch with highs recovering to near normal can be expected
through Tuesday. That changes Wednesday as a sharp upper-level
trough from northern Canada digs into the Upper Midwest.

A southwest breeze will develop and maintain seasonable
temperatures for at least part of the day, then a batch of rain
with slight chance of a thunder will arrive in the vicinity of a
cold front sweeping through. Among the model ensembles, there
remain differences in the arrival time of the cold front and rain,
making the difference whether most of the rain will fall during
the afternoon or at night. Low-level moisture return ahead of the
front and instability will be meager. A quarter inch of rain is
about the ensemble median amount, and NBM 75th percentile amounts
are closer to a half inch.

- Significant Late Week Cooldown with Showers

Thursday looks mostly dry with mid-level lid of warm and dry air.
Chances for showers increase Friday as a reinforcing shortwave
trough pinwheels around the deep upper-level low, followed by some
lake-effect rain showers lingering Saturday.

The amplitude of this low over the Great Lakes is remarkable for
the time of year. 500 mb height normalized anomaly Thu and Fri
over Michigan is projected to be around 3 standard deviations
below CFSR 1981-2010 climatology, per the EPS. Mean 850 mb
temperatures in the EPS are around 4 to 6 C, just a couple degrees
above the daily minimums recorded in the DTX sounding history.
What this translates to is daytime high temperatures in the upper
50s to lower 60s, within striking distance of record cold highs.
It should be fairly breezy and cloudy until the tail end of this
cold snap Saturday night, which keeps the frost potential for
central Lower Michigan on the lower side until then.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 240 PM EDT Sun Aug 31 2025

VFR conditions will continue overall. The sole exception once
again will potentially be JXN. Models are showing that another
round of MVFR to IFR vsbys will be possible between 06Z to 11Z.
Worst vsbys will be between 08Z to 11Z. Have adjusted TAF at JXN
accordingly. Otherwise light and variable winds with VFR will
dominate.

&&

.MARINE...
Issued at 240 PM EDT Sun Aug 31 2025

High pressure will continue to bring light winds and waves a foot
or less through mid-week. A Small Craft Advisory may be needed by
Wednesday and Thursday as low pressure moves through.

&&

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

&&

$$

DISCUSSION...CAS
AVIATION...Ceru
MARINE...Ostuno/Ceru