114
FXUS63 KGRR 101856
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
256 PM EDT Sun Aug 10 2025

.KEY MESSAGES...

- Periodic chances for showers and storms through Tuesday night

- Slightly cooler and drier mid week

- Heat returns next weekend

&&

.DISCUSSION...
Issued at 255 PM EDT Sun Aug 10 2025

- Periodic chances for showers and storms through Tuesday night

Periodic chances for showers and storms will occur through Tuesday
night as we will remain in a warm, humid and unstable airmass. A
washing out/weak cold front upstream in Wisconsin has driven bouts
of precipitation there, some of which that has been heavy
including flooding in the last 24 hours. A mesoscale convective
vorticity max can be seen spinning northeast out of Iowa this
afternoon which may provide a boost to the storms moving across
Lake Michigan as well as the activity increasing across Southwest
Lower Michigan. We have plenty of instability with MUCAPE values
at or above 2,000 j/kg and LI`s of -4. Bulk shear is still weak,
so not expecting severe. Anything close to severe would come in
the pulse variety or if storms can acquire enough of a cold pool
for a short time to provide some wind gusts in excess of 45 mph.
Overall severe chances are low/isolated this afternoon and
evening.

An increase in the low level jet overnight may bring another round
of showers and storms, especially up in our northwest forecast
area towards Ludington, Baldwin and Muskegon. On Monday models
indicate another round of showers/storms in our area, which may
involve much of the CWA. We really cannot rule out precipitation
until we get into Wednesday as a second stronger cold front moves
through Tuesday into Tuesday night.

We are not expecting widespread heavy rain, but most areas will
see some rain over the next 48-60 hours. The HREF is suggesting
some localized rainfall totals of around 2 inches possible. PWATs
are near that same value much of the time through Tuesday which is
indicative of a moisture laden profile.

- Slightly cooler and drier mid week

High pressure settles into the area on Wednesday and remains in
the region through Friday. We should be mainly dry during this
time with a drier airmass in place. Highs will be in the lower to
middle 80s Wednesday and Thursday which is closer to normals for
this time of year.

- Heat returns next weekend

The heat comes back next weekend when 850mb temperatures rise into
the upper teens C to around +20C. High temperatures increase once
again to around 90F. At this point we have a dry Saturday forecast
with small pops returning on Sunday. Model disparity (GFS has a
high on Sunday in the Great Lakes, while the ECWMF has a low)
leads to low confidence out on day 7.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 151 PM EDT Sun Aug 10 2025

We`re sitting on quite a bit of instability across western Lower
this afternoon. Radar shows some scattered showers have developed
northeast of GRR and much more showers/storms west of the lake.
The storms over Wisconsin may make it across the lake by late
afternoon and mainly affect MKG and we`ve included a prob30 for
that possibility. It`s also possible that a shower/storm could
develop near the other terminals too, but confidences on
when/where that would occur is low and was not included in the
TAFs.

Precipitation will diminish later tonight as instability decreases
leaving a mid and high cloud deck.

&&

.MARINE...
Issued at 255 PM EDT Sun Aug 10 2025

Have opted to drop the marine headlines (Small Craft Advisory and
Beach Hazard Statement) as conditions are just too marginal. Winds
and waves have not appreciably come up this afternoon and wave
model data supports conditions remaining below criteria.
Therefore, will be dropping both headlines shortly. 2-3 footers
looks as if that will be the peak this afternoon and that is more
of a moderate swim risk. Heading into tonight and Monday waves
will subside further.

A period of stronger south to southwest winds Tuesday into Tuesday
night looks to be our next chance for higher winds and waves.
Until then, mostly a low swim risk is expected.

&&

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

&&

$$

DISCUSSION...Duke
AVIATION...04
MARINE...Duke