669
FXUS63 KGRR 121050
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
650 AM EDT Wed Aug 12 2026
.KEY MESSAGES...
- Chance for Scattered Thunderstorms Today
- Saturday and Sunday is the Next Good Chance for Storms
- Seasonable Temperatures Expected
&&
.DISCUSSION...
Issued at 359 AM EDT Wed Aug 12 2026
- Chance for Scattered Thunderstorms Today
High resolution models all have a signal for scattered storms
today and the SPC outlook agrees with general thunder and a
marginal risk across the forecast area. Looking at the 24 hour max
reflectivity from the HREF there are two main zones for convection.
The first is in the SPC marginal risk across Central Lower
Michigan. Storms may both develop this morning and again this
afternoon over Central Lower, peeling to the southeast into the
thumb with time. The second area of focus is really just to the
south and west of the area like yesterday. The RAP is showing
1000-2000 j/kg of MUCAPE at max heating. Stronger mid level winds
are noted over Central and Northern Lower, so if there are chances
for severe weather today it will likely be up in Central Lower
with wind being the main threat.
- Saturday and Sunday is the Next Good Chance for Storms
We will largely be dry after this evening until we get to Saturday
night and Sunday when our next system will be working through the
state. A mid level shortwave looks to be the driver of this
convection as it tops the Central Plains ridge and moves through
the Great Lakes. Dew points surge into the 70s with MUCAPE values
in excess of 2000 j/kg so stronger storms are certainly possible,
especially given mid level flow around 40 knots.
- Seasonable Temperatures Expected
No major changes in temperature are expected. Highs look to be in
the 80s right through the 7 day forecast.
&&
.AVIATION /12Z TAFS THROUGH 12Z THURSDAY/...
Issued at 649 AM EDT Wed Aug 12 2026
Main concern today is the fog and stratus that is in place across
Southwest Lower Michigan. As expected widespread LIFR conditions
are occurring as we approach 11Z. The fog/stratus will not lift at
the same rate across the area due to the fact that the stratus is
not of uniform depth. Some areas will see the fog lift by 14Z-15Z,
but there will be pockets that likely persist into the afternoon.
By late afternoon, VFR weather should prevail once again.
The next threat we are watching today is the threat of
thunderstorms. At this time we feel the bulk of the activity will
stay to the north and south of the 6 TAF sites. We cannot rule out
some scattered activity impacted an airport or two, but at this
time confidence is not high enough to include.
&&
.MARINE...
Issued at 359 AM EDT Wed Aug 12 2026
Limited concerns in the next few days in terms of winds and waves.
We are in a fairly slack pressure gradient through the remainder
of the week so waves should be 2 feet or less. Otherwise, the two
main concerns are fog and thunderstorms. Thunderstorms are
possible today over Lake Michigan so mariners and beach goers will
need to keep that in mind as winds and waves are usually higher
in and near storms. Fog will remain a threat over the water until
we can bring in drier dew points. That does not really happen this
week so the threat of fog will continue.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Duke
AVIATION...Duke
MARINE...Duke
NWS GRR Office Area Forecast Discussion
