738
FXUS63 KGRR 030800
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
400 AM EDT Wed Sep 3 2025

.KEY MESSAGES...

- Wednesday showers and chance thunderstorm ahead of a cold front

- Friday wind and showers from a fast-moving low

- Cooler weather and frost potential into early next week

&&

.DISCUSSION...
Issued at 400 AM EDT Wed Sep 3 2025

- Wednesday showers and chance thunderstorm ahead of a cold front

Deep upper-level trough settling over Hudson Bay and the Great Lakes
through the rest of the week will be felt in Michigan starting
today, with the arrival of a cold front this afternoon and evening.
Prior to that, it will still be a seasonably warm day in southern
and south-central areas with a breeze from the southwest.

A few showers from midlevel clouds this morning will transition to
more numerous showers and embedded thunderstorms during afternoon,
as low-level moisture increases and mid-level lapse rates steepen
slightly, contributing to about 500 J/kg of CAPE (HREF mean). Deep-
layer shear around 20 knots and 20-30 knot flow above the surface
could allow for some gustier winds around 40 mph to accompany
thunderstorms, especially if a more robust updraft were to produce a
collapsing core of sub-severe hail.

Total rain amounts generally between 0.25 and 0.5 inches remain
favored, though HREF LPMM indicates the possibility for a few spots
pushing 1 to 2 inches where heavier downpours persist.

- Friday wind and showers from a fast-moving low

A vigorous shortwave trough reinforcing and rounding the base of the
larger-scale trough is likely to induce a compact and fast-moving
low pressure system over the western Great Lakes early Friday. The
wind field strength in the vicinity of the low will, at least for
several hours, be that of a true autumn gale. Depending on the exact
track of the low and associated frontal wave, a period of quickly
rising then falling temperatures is possible Friday morning along
with wind gusts that could warrant a short-duration advisory.

- Cooler weather and frost potential into early next week

The magnitude of the trough settling over the Great Lakes through
the rest of the week is quite anomalous, with 500 mb heights
reaching 3 standard deviations below normal over Michigan per the
EPS vs CFSR climatology. Daytime highs in the lower to mid 60s is
not too far from many cities` daily records for coldest highs. Once
the trough moves out and high pressure moves in early next week,
there will be a chance for frost in the typical cold spots of
Michigan`s interior, particularly Sunday night to Monday morning.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 206 AM EDT Wed Sep 3 2025

Multiple rain showers and chance of thunderstorms will move
through late morning into evening. The likelihood for MVFR
ceilings should reach MKG after 17 Z, then move east and
southeast, reaching JXN after 00 Z. Visibility may temporarily go
IFR under heavier rain showers or thunderstorms.

&&

.MARINE...
Issued at 400 AM EDT Wed Sep 3 2025

Increasing southwest winds today with showers and a few
thunderstorms over Lake Michigan. This will occur ahead of a cold
front which will shift winds northwest later in the day. High waves
and strong currents will build today, a hazard for small craft and
swimmers. Hazardous conditions are likely to continue into Saturday.
A Gale Warning may be needed eventually for Friday morning.

&&

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

&&

$$

DISCUSSION...CAS
AVIATION...CAS
MARINE...CAS