575
FXUS63 KGRR 102344
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
744 PM EDT Thu Jul 10 2025

.KEY MESSAGES...

- Thunderstorms Friday and Saturday, Severe Possible

- Lingering Showers and Thunderstorms Sunday, Mainly East

- Dry Monday and Tuesday, Rain and Storms Wednesday

&&

.DISCUSSION...
Issued at 327 PM EDT Thu Jul 10 2025

- Thunderstorms Friday and Saturday, Severe Possible

Overall there is uncertainty in the exact timing of rain and
thunderstorms due to differences in the overall pattern features.
However confidence is higher for showers and storms to move into
western Michigan early Friday morning from the remnant MCV over
western Wisconsin. This feature will cause thunderstorms to
redevelop overnight and move through the area Friday morning. Some
stronger storms are possible, but overall not expecting anything
severe with the morning round.

The morning convection looks to clear by the late morning/early
afternoon. Depending on how quickly storms clear will impact our
chance for afternoon thunderstorms which could be severe. At time
time the main window would be during the late afternoon and
evening hours. Mean HREF SBCAPE values are in the 1000-2000 J/kg
range during the afternoon mainly sough of I-96. 0-3 km storm
relative helicity values during that time are in the 100-200 m2/s2
range. Therefore there is enough spin in the atmosphere for
stronger storms producing hail, gusty winds, and perhaps a
tornado. This will be a higher concern with any remnant boundaries
in the area from the morning round of thunderstorms. This matches
up with the updated SPC outlook for Friday. Thunderstorms will
also produce heavy rainfall with precipitable water values
approaching 2 inches. Rainfall rates around an inch per hour are
possible. Areas that see thunderstorms track repeatedly overhead
could see higher rainfall amounts of 2 or more inches. This could
lead to minor flooding especially in urban areas. Friday night
thunderstorms will gradually diminish as we lose our daytime
instability.

Saturday a shortwave trough moves through the area bringing with
it another round of rain and thunderstorms for the afternoon and
evening. NBM 25th-75th percentile SBCAPE values range from
2000-3500 J/kg across much of the area, shear isn`t that great but
with that amount of instability it won`t take much for a storm to
become severe.

- Lingering Showers and Thunderstorms Sunday, Mainly East

Another shortwave through moves through Sunday which could spark
additional showers and thunderstorms during the day. Highest
chances are south and east of Grand Rapids but we`ll need to
monitor for a westward trend. Overall not expecting the day to be
a complete washout, but something to keep an eye on for those
with any outdoor plans.

- Dry Monday and Tuesday, Potential for Rain and Storms Wednesday

High pressure builds in for the beginning of next week with highs
in the 80s to low 90s and lows in the 60s to around 70. Wednesday
into Thursday a deeper, more organized trough looks to move
through the region. With the hot, moist environment it looks like
another good set up for thunderstorms.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 744 PM EDT Thu Jul 10 2025

Weakening showers and thunderstorms from upstream will arrive
after 08-09z tonight and cross the terminals through the morning
hours. Occasional reductions to MVFR conditions are likely in
heavier showers, particularly for MKG and GRR. Limited
instability will preclude thunder chances with this package.
Forecast soundings suggest a few hours of MVFR conditions behind
the showers at MKG. Afternoon conditions are somewhat uncertain at
this point as it will be highly dependent on how conditions
settle after the morning period. It is likely that in the
afternoon and/or evening a period of showers and thunderstorms
will develop across lower Michigan. Short range model guidance
varies highly as to how this evolves with storm arrival times
ranging from mid afternoon to after the TAF window. Given that
evening guidance will have a better handle on ongoing storms than
the previous guidance, will leave thunder out for now for the
afternoon. Whenever storms develop, the strongest will be capable
of IFR and lower conditions and gusty winds.

&&

.MARINE...
Issued at 327 PM EDT Thu Jul 10 2025

Short range models presently favor winds and waves remaining below
levels hazardous to small craft and beachgoers through the weekend.
However a low (around 20 percent) chance of hazardous winds and
waves exists later Friday into Saturday associated with a frontal
boundary crossing the area. The other marine concern is that several
rounds of showers and thunderstorms are likely through the weekend
beginning early Friday. Locally higher winds and waves are possible
in any storms, particularly later Friday and again on Saturday.
Mariners and beachgoers should monitor the forecast this weekend.

&&

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

&&

$$

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