399
FXUS63 KGRR 251129
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
729 AM EDT Wed Jun 25 2025

.KEY MESSAGES...

- Multiple Rounds of Rain and Thunderstorm Chances

- Hot and Humid Conditions Continue

&&

.DISCUSSION...
Issued at 323 AM EDT Wed Jun 25 2025

- Multiple Rounds of Rain and Thunderstorm Chances

Our next round of rain is thanks to a 700mb shortwave within the
moisture axis that moves in this morning. Current tracking of the
rain moving out of NE IL has it arriving in western
Muskegon/Ottawa counties around 4am. These showers will expand
eastward and likely flair up along the stationary boundary
currently south of I-96. Can`t rule out a rumble of thunder this
morning with MUCAPE values around 500 J/kg.

This afternoon most could remain dry with only isolated showers
and storms expected. The best potential will be along and south of
I-94 (30 to 40 percent). A few stronger storms are possible with
gusty winds, but the better potential looks to be south of the
area into northern Indiana which is highlighted by the current SPC
outlook.

Late this afternoon into tonight a warm front moves through from
south to north. A weak low level jet will also shift into the area
providing a source of lift along with warm air advection. This
lift could set up more north of M-20, hence the higher PoPs
overnight (50 to 70 percent). Scattered showers and thunderstorms
will remain possible until the front moves through Friday.
Thursday some strong to severe thunderstorms remain possible with
the potential for strong winds. The timing of the front will
determine our potential for strong to severe storms on Friday.

With precipitable water values around 2 inches now until the front
moves through, any shower or thunderstorm will be capable of heavy
rain. As seen yesterday as storms moved through Battle Creek,
rainfall rates over an inch per hour were observed. Those that see
storms track over the same area over a short amount of time could
see some flooding impacts, especially in known trouble spots.

Saturday looks to be a break in the rain, but additional
shortwave troughs bring back chances for rain and thunderstorms
Sunday into Tuesday.

- Hot and Humid Conditions Continue

Dew points remain largely in the 60s and 70s into next week keeping
the humid conditions in place. Today will be not as hot with highs
in the 70s and 80s, but after today 80s to low 90s are expected each
day into next week. This will result in heat index values
approaching 100 Thursday through the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 729 AM EDT Wed Jun 25 2025

Scattered rain is moving through the TAF sites this morning. Rain
is dropping visibilities down to a mile in spots along with
ceilings around 2500 feet. There are some areas of IFR to LIFR
ceilings near the low over south central Michigan. Can`t rule out
a few rumbles of thunder, but probabilities were not high enough
to add into the TAFs this morning. If storms occur, thunder will
be added in an amendment.

This afternoon isolated thunderstorms will be possible mainly
along and south of an AZO to JXN line. Strongest storms could
produce gusty winds. Another round of rain and thunderstorms moves
in mainly northwest of GRR late tonight into Thursday morning. Low
visibilities and MVFR ceilings will be possible with any
thunderstorm.

&&

.MARINE...
Issued at 323 AM EDT Wed Jun 25 2025

Winds and waves remain below Small Craft Advisory and Beach Hazard
Statement criteria into next week. The primary concern will be
the daily chances for thunderstorms. The best chances are overall
during the day, but the potential exists especially tonight and
Thursday night. Locally higher winds and waves are possible in any
thunderstorm.

Light north to northeast winds become more southerly tonight into
Thursday. Winds then shift behind the front Friday to the west to
northwest.

&&

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

&&

$$

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