799
FXUS63 KGRR 130710
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
309 AM EDT Thu Aug 13 2026

.KEY MESSAGES...

- Small chances of showers/storms through Friday; Mainly South

- Periods of showers/storms likely Friday night into Sunday

- Cooling off and drying out Monday through most of Wednesday

&&

.DISCUSSION...
Issued at 309 AM EDT Thu Aug 13 2026

- Small chances of showers/storms through Friday; Mainly South

As has been the case the past couple of days, the main ring of fire
convection axis has remained south of our forecast area. This is the
result of the stalled out boundary keeping the very hot and humid
conditions well south of the state, and the sfc waves riding along
it.

The models continue to show at least a couple of additional clusters
of storms just missing us to the south again. Based on the pattern
the last couple of days without any big push northward, this seems
very likely. Especially with another weak front dropping south
through the area early this morning. Can not rule out some rain
along the far southern edge of the forecast area on the northern
edge of any cluster.

- Periods of showers/storms likely Friday night into Sunday

We do see some changes in the pattern showing up beginning Friday
night, and lasting into Sunday. This change in the pattern is
facilitated by a long wave trough taking hold over the Western third
of the country. This wave then ejects a couple of short waves and
sends them via a more SW flow aloft toward the area.

This pattern shift then also pushes the boundary further north,
bringing the higher heat and humidity closer to the area. With short
waves riding along this front, we will see MCS activity ramp up once
again with the associated low level jets traversing over our
southern area, or staying just south and the nose of them aiming
toward the area. We will need to keep an eye on this as we could see
strong to severe storms be possible while we are under the theta e
axis and short wave train.

This really looks possible from Friday evening all the way into
Sunday. On Sunday, we see a general trend in the pattern showing
that everything sinks south as the SW flow aloft and upper ridge
gets flattened a bit. This includes the baroclinic zone and active
zone for MCS activity, along with cooler weather filtering in.

- Cooling off and drying out Monday through most of Wednesday

The front will sink south through the area no later than Sunday,
taking with it the moisture and instability, and shunting it to our
south by Monday. Upper and sfc ridging will build in for Monday
through at least early Wednesday, keeping us dry. There are some
indications the next wave could come in late next Wednesday. We have
time to fine tune the timing of this.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 120 AM EDT Thu Aug 13 2026

Our main focus with this set of forecasts is on the fog and low
cloud potential for all of the terminals. A weak front dropping
down across the area is interacting with a moist air mass with
lighter winds. This is a very good set up fog fog. We are starting
to see some MVFR conditions develop, and conditions are expected
to drop further into the IFR to LIFR category over the next couple
of hours.

The lower conditions will remain until about 13-15z, before the
fog mixes out, and clouds break up. This will allow for VFR
conditions to develop and remain for the rest of the period.

&&

.MARINE...
Issued at 309 AM EDT Thu Aug 13 2026

No wind or wave headlines are expected through at least Friday. The
pattern we are in through Friday is that of a weak pressure pattern,
resulting in lighter winds and waves. We can not rule out needing
some fog headlines given the weak winds and moist air mass.

There is some uncertainty as to when the winds and waves may be
strong enough to necessitate Small Craft Advisories and Beach
Hazard Statements. The latest trend is for better winds aloft moving
overhead Friday night, However being warmer winds, those may very
well stay aloft. The potential for winds and waves will last through
much of the weekend until the system moves far enough away.

&&

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

&&

$$

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