734
FXUS63 KGRR 131142
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
742 AM EDT Fri Jun 13 2025

.KEY MESSAGES...

- A Few Showers Mainly South of I-96 Through Saturday

- Dry for Most Areas Sunday into Monday

- Midweek pattern: Humid with Thunderstorms at Times

&&

.DISCUSSION...
Issued at 308 AM EDT Fri Jun 13 2025

- A Few Showers Mainly South of I-96 Through Saturday

Elevated instability drops to almost nothing today, and as such we
are only expecting a few showers to pop during the day as dew
points recover to around 60F after falling this morning. With a
general lack of synoptic forcing present, nothing very organized
will develop with just hit and miss shower activity and many areas
staying completely dry. A similar situation is in place late
tonight into Saturday morning, with perhaps a better shot at
showers near and south of I-94 before exiting out of the region
Saturday afternoon

- Dry for Most Areas Sunday into Monday

The majority of medium range guidance keeps the region dry Sunday
and Monday. A light lake breeze develops Sunday and the inland-
moving lake modified air will interact with easterly surface flow
and low 60s dew points to help generate some cumulus, but likely
not any showers at this point. The ECMWF is indicating zero MUCAPE
so that should help keep things in check. For Monday, there is a
slight chance for some showers and perhaps a thunderstorm as a
subtle 500 mb shortwave trough moves through and weak 850 mb winds
may try to converge across WI / Lake Michigan and angle into the
region. The ECMWF is the main model showing this scenario and as
such POPs are not high at this time.

- Midweek pattern: Humid with Thunderstorms at Times

A noticeable uptick in humidity will occur Tuesday through
Wednesday as dew points start knocking on the door of 70F. This
occurs as a synoptic pattern change will be underway. Ensemble
guidance is favoring a 500 mb trough and an enhanced mid level jet
moving into the Midwest by Wednesday. A fairly strong upper level
jet for mid June is forecast to move through at that time (90 to
100 knots). Equally important will be a much more dynamic low
level jet moving in than we have seen recently, with 40-50 knots
shown by the GFS, GEM, and ECMWF. There are just some timing
differences at this point but good confidence on the existence of
a solid LLJ mid week. Organized and potentially strong
thunderstorms are possible during the midweek period, with early
thoughts suggesting Wednesday may have the best potential. This is
also supported by NSSL`s machine learning severe weather
probabilities and NCAR`s AI NWP-based forecasts favoring the Great
Lakes for some severe weather potential.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 738 AM EDT Fri Jun 13 2025

Scattered showers continue popping up this morning as both IR and
water vapor satellite imagery indicate thickening clouds and
increasing mid level moisture moving into the region. Cloud bases
are commonly around 5000 ft and they`ll likely be right around
there through the duration of the day. Not expecting thunderstorms
to impact the terminals with waning instability aloft. In the
00z-06z window, our southern terminals have a better risk for more
frequent showers or perhaps even a steady light rain (especially
JXN). Lowering cloud bases to just above IFR are forecasted for
AZO, BTL, and JXN during that time. Will have to keep an eye on
the northern extent of IFR as it could potentially reach those
terminals but for now the favored scenario is MVFR.

&&

.MARINE...
Issued at 308 AM EDT Fri Jun 13 2025

Waves generally 1 foot or less are expected through the weekend
with offshore flow today into part of Saturday before some weak NNW
flow takes over during the afternoon hours of Saturday and Sunday.
These winds are not expected to increase wave activity at this
time but trends will be monitored.

&&

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

&&

$$

DISCUSSION...Hoving
AVIATION...Hoving
MARINE...Hoving