Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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438
FXUS63 KGRR 110554
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
154 AM EDT Fri Jul 11 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 /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 154 AM EDT Fri Jul 11 2025

Convective trends are our main focus with the 06z set of
forecasts.

We are watching an area of rain with embedded thunder down toward
Chicago and Milwaukee as of 0530z. This is moving toward the area,
but is trending down for the time being. We do expect additional
development to take place, and affect all of the terminals this
morning into early afternoon. Showers are expected to move over
KMKG by 10-11z, and then spread eastward from there through the
morning. Thunder chances look to lag the showers by a couple of
hours. We do expect conditions to drop down into the IFR category
with the storms and heavier rain rates. These showers and storms
are then forecast to move east of the terminals by 18z or so.

There will be a relative break in the more widespread
showers/storms after the morning batch moves out. The chance will
not be zero of an isolated shower/storm popping up, but the
coverage will be 10-20%, so have not included it in the forecast.

We will be watching another potential wave of showers and storms
moving into the area late evening to early overnight. This is a
bit uncertain yet, but looks to favor the KMKG and KGRR terminals.
Have mentioned thunder there, and left the rest of the terminals
dry for now. We will fine tune this as trends unfold through the
day with features.

&&

.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...NJJ
MARINE...Thomas