641
FXUS63 KGRR 270549
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
149 AM EDT Fri Jun 27 2025

.KEY MESSAGES...

- Highest Chances for Rain will be Friday and Monday

&&

.DISCUSSION...
Issued at 217 PM EDT Thu Jun 26 2025

Diurnally-enhanced convection along a warm front will persist
into this evening then should diminish overnight. More storms will
fire up on Friday in the warm sector and ahead/along a cold front
as a sfc low tracks across northern Lower Michigan. The front
clears southeast zones late Friday night with a brief period of
fair weather and lower dew points into Sunday morning.

By Sunday afternoon, return flow is already setting up as a
shortwave trough embedded in zonal flow moves from the Plains
into the Great Lakes. Dew points surge back into the 70s by Monday
with a cold front arriving by afternoon. Instability is
sufficient for enhanced thunderstorm coverage but deep layer
shear is only around 20 to 25 knots, so storms may be more of the
pulse variety.

Dew points behind the front fall into the 50s to lower 60s for
Tuesday through Thursday offering a break from the recent
oppressive humidity. Long range indications are for the
possibility of some storminess on the 4th, but confidence is low
in the details.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 149 AM EDT Fri Jun 27 2025

Scattered thunderstorms are currently moving through the area and
will likely push east of LAN and JXN around 8-10Z. Meanwhile
additional showers and storms are developing over Lake Michigan
and Wisconsin which are expected to move east into the area around
the same time. Highlighted the timeframes where showers and
thunderstorms were more likely in the TAFs for any one location.
MKG, GRR during the morning and early afternoon, and AZO to LAN
and south during the afternoon to early evening hours. There is
still some uncertainty as thunderstorms are not expected to be
widespread, so used Prob30s for the storm potential.

As with the previous rounds of thunderstorms, heavy rainfall with
rates around an inch per hour are likely with any thunderstorm.
Gusty winds are also possible, but the better wind threat will be
toward JXN and LAN this afternoon. If thunderstorms impact any one
location IFR visibilities and MVFR ceilings are possible.

Dry conditions return by 00Z Saturday with winds from the west to
northwest.

&&

.MARINE...
Issued at 139 PM EDT Thu Jun 26 2025

Waves will build to around 2 feet north of Holland Friday
afternoon. Otherwise waves will generally be less than 2 feet for
the next couple of days.

Thunderstorms remain a possibility this afternoon and again Friday
afternoon.

&&

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

&&

$$

DISCUSSION...Ostuno/RAH/Thomas
AVIATION...RAH
MARINE...RAH