651
FXUS63 KGRR 081833
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
233 PM EDT Sat Aug 8 2026

.KEY MESSAGES...

- Periods of showers and storms Sunday afternoon into Monday

- Mainly small daytime shower/storm chances Tuesday and Wednesday

- Cooler late week with returning chances of rain

&&

.DISCUSSION...
Issued at 233 PM EDT Sat Aug 8 2026

- Periods of showers and storms Sunday afternoon into Monday

We are seeing some slightly cooler and drier air filter over the
area this afternoon in the wake of a cold frontal passage earlier
today. This will remain the case through Sunday morning.

We will see shower/storm chances increase from West to East across
the area Sunday afternoon. A majority of model data shows a complex
of showers and storms coming in after 18z for most of the
southern two thirds of the forecast area.

These will be supported by a low level jet that will be weakening as
the nose of it moves toward the area. In addition, these
showers/storms will be moving toward an area that is much less
unstable due to the air mass replacement that took place today. MU
CAPEs are forecast to be less than 1000 J/kg by late afternoon, with
a stronger gradient of instability to our south. These factors will
significantly limit strong to severe storms Sunday afternoon.

We expect additional showers/storms to develop to our SW Sunday
evening as another low level jet ramps up with another MCV/short
wave that will be riding along the instability gradient. The window
between the afternoon and evening storms may be so short, that
outflow boundaries, or just the tail of the storms might be acted
upon by the new low level jet.

The significance of this could be that we see backbuilding off of
the first line of storms, that could lead to some training of storms
and a potential flooding threat. A flooding threat looks more
possible up in our area over the southern counties, than a severe
threat, as the instability is more elevated, and the forcing from
the low level jet will be focused over our extreme southern area,
and further south. Precipitable water values look to max out just
south of our area too just short of 2.0". It is still very healthy
over much of our area being around 1.8" or so.

This is all likely to push south of the area by Monday afternoon the
low level jet moves by, and likely pushes the best moisture axis
just south of the area. The models seem to be trying to pop some
diurnal showers/storms Monday afternoon with much of the area seeing
1000-1500 J/kg of CAPE present.

- Mainly small daytime shower/storm chances Tuesday and Wednesday

The edge of the heat dome (and best instability) will sink a bit
further south by Tuesday and Wednesday, but we do not see a major
change in air masses for our area. Temperatures will still max out
in the 80s mid week, and dew points will remain in the 60s. We will
be a bit closer to the jet stream, with weak short waves potentially
sparking a few showers/storms off mainly during the afternoon and
evening hours.

- Cooler late week with returning chances of rain

The threat of rain looks to almost disappear for a couple of days
for Thursday and Friday. It is at that time that we see high
pressure over Ontario bring in a flow from the NE that dries us out
a bit more. This will take away lingering instability from Tue/Wed,
with a short wave ridge also helping to keep us dry.

The dry weather potential looks to remain short lived as we will see
the upper flow become from the SW. This will try to push the edge of
the heat dome toward the area again, with short waves riding along
the flow that could tough off showers and storms beginning as early
as Friday night into Saturday.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 128 PM EDT Sat Aug 8 2026

High confidence for VFR conditions at all terminals through 06Z
with winds becoming light towards midnight. Current cloudiness is
diurnally driven and we expect clear skies below 18000 ft
beginning around or after sunset. Did include a tempo group for MVFR
visibility restrictions prior to and around sunrise Sunday at
KAZO but this outcome is far from certain.

&&

.MARINE...
Issued at 233 PM EDT Sat Aug 8 2026

As expected, we had some elevated waves heights earlier with the
peak of the wind just ahead and just behind the cool front that
moved through. Waves got up to around 3+ feet, but are now on the
downturn. We should see a lull in the winds and waves through
tomorrow morning.

Winds and waves will once again increase Sunday afternoon ahead of
the next wave of low pressure expected to approach the area. We
believe these winds and waves will end up just below criteria, so no
headlines for now. Showers and storms will increase Sunday
afternoon, and some of these could create some short term issues.

&&

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

&&

$$

DISCUSSION...NJJ
AVIATION...TJT
MARINE...NJJ