523
FXUS63 KGRR 021826
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
226 PM EDT Tue Sep 2 2025

.KEY MESSAGES...

- Wednesday cold front and associated thunderstorm chances

- Friday cold front and wind

- Cooler weather and frost potential

&&

.DISCUSSION...
Issued at 226 PM EDT Tue Sep 2 2025

- Wednesday cold front and associated thunderstorm chances

Rain chances with our next system begin as early as tonight, but are
centered on Wednesday afternoon and night. A strong cold front is
poised upstream over Northern Minnesota, which is set to move
through Southwest Lower Michigan Wednesday afternoon and evening.
The cold front is supported by a strong upper low that is plowing
south across Manitoba and Saskatchewan this afternoon. Surface dew
point surge to 60-65F between 10am and 10pm across our forecast area
and that is when we expect the highest chances for rain and
thunderstorms. We feel MUCAPE values will surge to 1,000 to 1,500
j/kg during the heat of the day. The stronger shear lags the front
so not expecting significantly organized storms which is why we
are only in a General Thunder outlook from the SPC. That said,
with lower freezing levels, 10,500 feet, plenty of instability and
30 knots of wind at 850mb there is potential for some hail
(0.50" to 0.75") and some wind gusts of 40-50 mph. The strength
of the cold front should drive some embedded fairly vigorous
convection, just likely sub severe. Rain moves into the Ludington
area towards daybreak with the best chance at some stronger cells
occurring mid afternoon from South Haven northeast through Grand
Rapids to Mt. Pleasant. Chances for rain tomorrow will be north of
70 pct in all areas. The rain will linger into Wednesday night
before drying out a bit into Thursday

- Friday cold front and wind

Thursday night another cold front approaches with rain chances
increasing late and especially into Friday. There will likely be a
lake boost to the rain showers with the second front given lake
water temps per overnight satellite passes of 68F to 72F degrees
over much of the south half of the lake. Using a 21C average
temp, we will be pushing delta T`s on Friday into the upper teens
C. Plenty of instability (500-800 j/kg), although moisture depth
is on the lower side. A solid area of rain showers, possibly
embedded with a rumble of thunder (much lower chance than Wed)
will move through the area.

Another element to the very fallish weather that we will need to
keep an eye on is the wind on Friday. A sub 1000mb low will push
northeast through the Great Lakes on Friday with when combined with
a 1018mb high in the plains we will see a windy day on Friday. Some
models have us tapping into wind that is 40+ mph. We will be
monitoring for potential wind headlines. At this point a wind
advisory looks marginal, but its close. The surge in wind really
looks to come in early maybe even before daybreak lasting into the
day.

- Cooler weather and frost potential

Overall, this is a fairly significant change in the weather. High
temperatures today will be around 80F with temps tumbling through
the week. Highs Thursday through Sunday will be in the 60s in many
areas with 50s even across interior Central Lower Michigan. We have
lows in our forecast Saturday night and Sunday night dipping into
the 30s in spots up along U.S. 10 in Central Lower. So, there will
likely be some frost up there on those nights, especially for
traditionally cold places like Leota in Clare County. Talking delta
T`s, potential wind advisories and plenty of lake effect
clouds and rain showers...fall is here!

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 125 PM EDT Tue Sep 2 2025

A cold front will move across the terminals Wednesday afternoon.
Ahead of it, showers will develop. MKG will most likely see some
rain prior to 18z, but the rest of the terminals will see
precipitation after 18z. Cigs will lower Wednesday morning, but
remain VFR.

&&

.MARINE...
Issued at 125 PM EDT Tue Sep 2 2025

Winds will increase ahead of a strong cold front Wednesday. Waves
will increase to at least 3 feet around sunrise; we`ve issued a
small craft advisory and beach hazards statement from 6am
Wednesday through 8 am Saturday. Wind and waves will be hazardous
to small craft and beach goers. Additionally, scattered thunderstorms
Wednesday will also pose a threat.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from Wednesday morning through Saturday
     morning for MIZ037-043-050-056-064-071.
MARINE...Small Craft Advisory from 6 AM Wednesday to 8 AM EDT Saturday
     for LMZ844>849.

&&

$$

DISCUSSION...Duke
AVIATION...04
MARINE...04