677
FXUS63 KGRR 132337
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
737 PM EDT Fri Jun 13 2025

.KEY MESSAGES...

- Showers south of I-96 into Saturday Morning

- Mostly Dry Saturday into Monday

- Humid with Thunderstorms Midweek

&&

.DISCUSSION...
Issued at 319 PM EDT Fri Jun 13 2025

- Showers south of I-96 into Saturday Morning

Positive vorticity advection associated with the low centered
over Missouri will continue to provide lift for the showers that
have filled in over southern Michigan. These showers will continue
through tonight before shifting east of the area Saturday
morning. We are not expecting any thunder with this activity due
to the lack of instability. There is plenty of moisture in place
however with precipitable water values around an inch and a half
moving into southern Michigan. Within the moist environment there
is the potential to see a quarter of an inch of rain with the best
chances (40 to 50 percent) south of I-94.

- Mostly Dry Saturday into Monday

High pressure builds into the area over the weekend with light
easterly winds continuing. Temperatures are expected to be in the
70s tomorrow and warming into the mid 80s by Monday. The lake
breeze Sunday may keep temperatures in the 60s and 70s along the
lakeshore.

There is a slight chance (20 to 30 percent) for showers and
storms Monday as a disturbance moves out of Wisconsin and across
the lake into Michigan. Within our moist environment, any source
of lift could spark off showers and thunderstorms (if instability
is present).

- Humid with Thunderstorms Midweek

Tuesday we become more embedded in the southwesterly flow with
warming temperatures and increasing moisture. Highs in the 80s are
expected with heat index values around 90 Tuesday across much of
the area and again on Wednesday toward Calhoun, Jackson, and
Ingham counties.

With the increase heat and moisture also means an increase in
instability. Chances for showers and storms increase from 30 to 40
percent Tuesday to 60 to 70 percent Wednesday/Wednesday night.
These higher chances are tied to better lift provided by a
shortwave trough expected to move through the region. There are
still some differences in timing but overall with instability,
moisture, and lift in place, expect scattered showers and
thunderstorms for much of the area midweek. Currently the best
window for a quarter of an inch or more of rain is Wednesday night
with much of the area having a 60 to 70 percent chance based on
the NBM probabilities. We will need to monitor the potential for
severe storms as well with the low level jet in play over the
area. As mentioned before the potential for severe storms is
highlighted in NSSL`s machine learning probabilities and NCAR`s AI
NWP-based forecasts. With these factors, the convective outlook
from the SPC may be expanded over Michigan as we get closer.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 737 PM EDT Fri Jun 13 2025

Light rain in southern Michigan to persist through much of the
early part of the TAF period with AZO, BTL and JXN seeing some
potential for MVFR conditions at times. Best chance for MVFR
conditions should be before 12z with improvement after that.
Otherwise...VFR conditions expected.

&&

.MARINE...
Issued at 319 PM EDT Fri Jun 13 2025

Easterly winds will keep wave heights around a foot or less
through the weekend and into Monday. Winds become more southerly
Monday afternoon into Tuesday with the potential for showers and
thunderstorms.

Water temperatures remain cool in the mid 50s to 60s, but with the
hot temperatures expected into next week these should slowly rise.

&&

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

&&

$$

DISCUSSION...RAH
AVIATION...Maczko
MARINE...RAH