229
FXUS63 KGRR 271854
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
254 PM EDT Fri Jun 27 2025

.KEY MESSAGES...

- Strong to Severe Storms into this Evening

- Cooler and Drier Saturday then Warmer and Wetter Sunday and
  Monday

- Fair and Drier Tuesday through Thursday

&&

.DISCUSSION...
Issued at 253 PM EDT Fri Jun 27 2025

- Strong to Severe Storms into this Evening

A line of strong storms that initiated along a horizontal roll
circulation this afternoon is expected to continue propagating
east and expand northeast through early evening before departing
the eastern zones later this evening. Despite moving into and area
of higher instability with CAPE of 1500 to 1800 j/kg, only modest
strengthening is expected as deep layer shear is relatively weak
and has so far precluded organized, sustained updrafts.

Main threats will be isolated downburst winds over 60 mph and hail
near 1 inch in diameter.

- Cooler and Drier Saturday then Warmer and Wetter Sunday and
  Monday

Cold front moving through overnight will usher in a welcome
change of airmass with the oppressive 70 degree dew points
dropping into the comfortable range of upper 50s to lower 50s dew
points for Saturday and Saturday night. This will be a brief
respite as return flow is already setting up ahead of a shortwave
trough embedded in zonal flow moving from the Plains into the
Great Lakes. Dew points surge back into the 70s by late Sunday
into Monday with a cold front arriving by afternoon.

Instability is sufficient for enhanced thunderstorm coverage but
deep layer shear is once again limited, only around 20 to 25
knots, so storm mode may be of the pulse variety.

- Fair and Drier Tuesday through Thursday

Another cold front moves through Monday night and this will bring
a longer stretch of comfortable temperatures and dew points
lasting through Thursday. The long range indications are for
shower/thunder chances on the 4th, but confidence remains low at
this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 148 PM EDT Fri Jun 27 2025

Showers and storms are the concern for the early part of the
period. Radar shows developing storms ahead of a cold front. These
storms should miss MKG and probably GRR, but we`ve included a
TEMPO for the other terminals for a few hours later this
afternoon. The threat should pass from west to east by early
evening leading to a broken VFR cloud deck.

&&

.MARINE...
Issued at 157 PM EDT Fri Jun 27 2025

We`ll be watching showers and thunderstorms develop this afternoon
mainly south of MKG as a cold front moves east. Waves will
generally be around a foot through Sunday. However, north of MKG,
waves will build to 2-3 feet by Sunday afternoon.

&&

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

&&

$$

DISCUSSION...Ostuno
AVIATION...04
MARINE...04