367
FXUS63 KGRR 111057
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
657 AM EDT Tue Aug 11 2026

.KEY MESSAGES...

- Storms possible today across Southern Lower Michigan

- Less confidence in storms on Wednesday

- Drier weather settles in for the latter half of work week

&&

.DISCUSSION...
Issued at 343 AM EDT Tue Aug 11 2026

- Storms possible today across Southern Lower Michigan

The focus today is on the warm front to our south which stretches
from portions of Iowa into Indiana. A low level jet max at 850mb
will work eastward down the warm front this morning which should
bring continued development to convection near and north of the
front off to our west. A marked increase is convective coverage
has been noted in the past 1-2 hours from the MI/IN border region
through Southern Wisconsin to far Southeast South Dakota. All of
this activity is working eastward with the mid level flow towards
Southern Lake Michigan. MUCAPE values are significant even at this
hour with the RAP indicating 2000-5000 j/kg. Given a low level jet
forcing the activity and a large reservoir of instability the
activity will no doubt continue/expand. Agree with both the SPC
day 1 outlook and machine learning guidance like NadoCast
indicating the far southwest corner of the state stand the best
chance at severe weather today. Areas to the south and west of
Grand Rapids will be the area of concern between 14Z and 21Z.
Winds looks to be the main threat.

- Less confidence in storms on Wednesday

Wednesday we will remain under zonal upper flow with what looks to
be convectively driven vorticity maxima working through the area,
at least in the GFS. The SPC day 2 outlook shows general thunder
to marginal risk levels across the forecast area. We seem to lack
a trigger on Wednesday with no major shortwave aloft, no low level
jet to speak of aimed at the region and a surface warm front that
will likely remain situated in Illinois and Indiana. Given MUCAPE
values in excess of 2,000 j/kg we have thunder in the forecast.

- Drier weather settles in for the latter half of work week

Surface high pressure gradually builds in and takes over our
weather for Thursday and Friday. BUFKIT overviews look dry for the
most part from Wednesday night through Friday night. High
temperatures actually trend back into the 70s from Friday into
Saturday.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 657 AM EDT Tue Aug 11 2026

Shallow morning fog is in place across the area at 12Z and this
should lift rather quickly through 14Z. A stationary front off to
our south across Illinois and Indiana will be a focus for showers
and thunderstorms. This activity has a chance to move through some
of the TAF sites today between roughly 15Z and 21Z. The area we
are watching are the storms across Iowa. They will slide to the
east and southeast and have the best chance of impacting AZO and
BTL. At present it is moving east which would allow it to impact
more TAF sites. We expect a slight turn to the southeast with
time though. The showers and storms should come to an end this
afternoon and early evening. MVFR and IFR conditions are possible
with storms. We should clear out tonight with fog developing.

&&

.MARINE...
Issued at 343 AM EDT Tue Aug 11 2026

A typical mid summer weather pattern will be in place the next
few days, meaning light winds due a slack pressure gradient. This
type of regime is common in August when we often see light winds,
sunshine and some of our warmest water temperatures. Current water
temperatures at the buoys...Michigan City 79, Cook/Bridgman 74,
South Haven 73.

As far as winds and waves go we will see winds of 15 knots or less
generally which will produce a limited wave field of 2 feet or
less the next few days. The main exception is that winds and
waves could be higher in and near thunderstorms. There is a signal
in the high resolution models indicating storms sweeping the
southern portion of the lake, near and south of Holland between
15Z and 21Z. Waves may briefly be higher down in that zone if
storms sweep the lake.

&&

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

&&

$$

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