589
FXUS63 KGRR 021128
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
728 AM EDT Tue Sep 2 2025

.KEY MESSAGES...

- Next Chance for Rain on Wednesday

- Upper troughing brings cool, showery weather into the weekend

&&

.DISCUSSION...
Issued at 141 AM EDT Tue Sep 2 2025

- Next Chance for Rain on Wednesday

Despite a highly amplified and somewhat blocky flow regime more
typical of autumn than late summer, the models are in a fairly
good agreement on the details of the timing of the pattern
evolution over the next several days.

We start off with a surface high moving east and a quick breakdown
of a rex block across the Great Lakes as a vigorous upper low
dives southeast from Canada and carves out a longwave trough
across the central and eastern CONUS by late in the week. Moisture
streaming up from the south will converge with the trough axis
and a surface low trailing a cold front by Wednesday afternoon and
evening with showers and thunderstorms possible. Precipitable
water values spike up to over 1.25 inches late Wednesday, so some
decent rain rates are possible, although storm motion appears to
be around 40 knots, limiting the potential for excessive rainfall.

- Upper troughing brings cool, showery weather into the weekend

Diurnally driven showers with some lake enhancement are possible
on Thursday through next weekend, especially early Friday, when
model guidance shows a strong shortwave trough and vorticity
maxima rotating around the upper low in broad cyclonic flow
regime along with steep mid level lapse rates.

An unusually cold airmass for early September builds in by the
weekend with temperatures well below normal. Some scattered frost
is possible in the northern interior zones if skies clear and
winds decouple on Saturday or Sunday nights. At this point it
appears Sunday night will see some clearing as high pressure
builds into the central Great Lakes.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 728 AM EDT Tue Sep 2 2025

VFR conditions will continue through tonight. Rain arrives
Wednesday but after 12Z. Winds will continue relatively light
today and tonight, around 5 knots.

&&

.MARINE...
Issued at 141 AM EDT Tue Sep 2 2025

High pressure will bring light winds and waves a foot or less on
Tuesday. A Small Craft Advisory will be needed by Wednesday and
continuing through the weekend as persistent strong onshore flow
develops along with the chance for waterspouts.

&&

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

&&

$$

DISCUSSION...Ostuno
AVIATION...Ostuno
MARINE...Ostuno