570
FXUS63 KGRR 261155
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
755 AM EDT Sat Jul 26 2025

.KEY MESSAGES...

- Potentially a couple rounds of showers and storms today

- Another chance for showers and storms on Monday

- Turning drier and cooler mid to late week

&&

.DISCUSSION...
Issued at 355 AM EDT Sat Jul 26 2025

- Potentially a couple rounds of showers and storms today

A series of weak convectively induced vort maxima are located
within southwest flow aloft stretching from Northern Indiana
southwest to Northeast Kansas. These vort maxima will traverse the
Southern Great Lakes region from early this morning through this
evening, likely resulting in rounds or periods of showers and
thunderstorms. The first period we expect storms is towards
daybreak and through the morning hours. Both high resolution and
global models indicate a surge in the nocturnal low level jet
aimed right into Southwest Lower Michigan around 800am. We are not
too concerned about severe weather with this wave of activity, but
locally heavy rain is quite possible given PWAT values approaching
2.25 inches. Local swaths of 1-2 inches of rain look like a good
bet this morning per the HREF.

We may see a lull in the activity in the early to mid afternoon in
the wake of the morning convection followed by another potential
round in the late afternoon and especially the evening hours as
the last in the train of shortwaves work through the Southern
Great Lakes. There is a surge in wind speeds this afternoon and
evening with the 850mb LLJ increasing to around 30 knots and the
mid level jet at 500mb increasing to 40+ knots. Deep layer shear
increases to 30-35 knots so storm organization can be expected. If
we can realize enough instability this afternoon in the wake of
the morning precipitation a marginal severe weather threat exists
(we are in a SPC marginal threat today). Main threat looks to be
wind with this activity. Threat area looks to be from the I-96
corridor to the south. Multiple rounds of rain today into early
tonight may put down 2.00 to 3.00+ inches of rain in spots per the
HREF. We should be able to absorb this rainfall into the rivers
without much of an issue, but short term ponding of water may
occur in the torrential downpours.

- Another chance for showers and storms on Monday

Another round of showers and storms looks possible on Monday with
a weak cold front moving through the region. The main shortwave is
well off to our north however and the chances for widespread
precipitation look smaller than they did a day or two ago for
Monday. Still, some scattered showers and storms look like a good
forecast, especially across Central Lower Michigan closer to the
upper support.

- Turning drier and cooler mid to late week

We look to turn cooler and drier as we head into the Wednesday
through Friday period. A large upper low over eastern Canada
nudges southward into the Great Lakes region during this time
frame resulting in cooler air infiltrating the area at 850mb. By
Friday 850mb temperatures actually dip to +8C to +9C which should
result in very pleasant temperatures for those looking for a
respite from the heat and humidity. Our forecast highs by the end
of the week are in the 70s with dew points even dipping into the
40s. The latter half of the work week looks dry with surface high
pressure firmly in control.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 754 AM EDT Sat Jul 26 2025

Lower ceilings are trying to fill in this morning across the TAF
sites. A mix of conditions are occurring at 12z, with VFR
conditions at MKG to IFR at GRR and BTL. We expect lower ceilings
to fill in at most TAF sites this morning to at least MVFR. The
lower ceilings will lift north with time and we expect all sites
to trend to VFR this afternoon.

Rounds of showers and storms can be expected today. Scattered
showers are anticipated this morning, which should then be
followed by a more steady period of rain from about 15z to 18z or
so. This is the activity moving our direction from IL.

This evening is more of a low confidence forecast with potentially
another round of showers and storms. For now have some VCTS
wording in the TAFs between roughly 22z and 02z.

Winds will be southwest today at 5 to 15 knots.

&&

.MARINE...
Issued at 355 AM EDT Sat Jul 26 2025

The quiet conditions out on the big lake look to continue through
the weekend and into Monday and Monday night. The light winds
initially this weekend are provided by surface ridging meaning a
fairly slack gradient in place. Into early next week a weak front
moves through which keeps the gradient on the slack side. So, we
are expecting winds generally in the 5 to 15 knot range the next 3
days or so with waves of 2 feet or less. Winds and waves will be
briefly higher in and near thunderstorms both today and again on
Monday.

&&

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

&&

$$

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