286
FXUS63 KGRR 071730
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
130 PM EDT Fri Aug 7 2026
.KEY MESSAGES...
- Showers and storms possible this afternoon through Saturday
- Storms possible Sunday into Monday
- Trending slightly cooler and drier into mid next week
&&
.DISCUSSION...
Issued at 354 AM EDT Fri Aug 7 2026
- Showers and storms possible this afternoon through Saturday
Small chances for showers and thunderstorms exist this afternoon
and early evening to the southeast of Grand Rapids. Areas from
Kalamazoo to Lansing and Jackson stand the best chances to see
this activity but it is not certain. The HREF does not have a good
handle of convective chances today. The HRRR and other high
resolution models seem to be picking up on a signal for this area
where MUCAPE values may exceed 1500 j/kg. If storms develop not
expecting severe weather given low shear and only modest
instability.
Tonight there is a threat that some stronger storms may try to
advect in from the west overnight along and ahead of a cold front.
Machine learning schemes are not bullish on severe weather today
or tonight though and the SPC only has our area in a general
thunder outlook. Shear remains weak tonight.
- Storms possible Sunday into Monday
A better chance at some stronger storms looks to occur in the
Sunday into Monday time frame as a warm front sets up to our
southwest. This is when surface dew points (around 70) and PWAT
values (1.75 to 2.00 inches) peak in the 7 day forecast. Embedded
shortwaves in a generally zonal upper flow will likely aid in
thunderstorm initiation and maintenance. A 25-35 knot low level
jet will also aid storms. MUCAPE values will push towards or
potentially exceed 2000 j/kg. Sunday night and Monday will likely
be the best chance at storms. SPC maintains a general thunder
outlook for us on Sunday and Monday as well.
- Trending slightly cooler and drier into mid next week
We trend a bit cooler into mid week as 850mb temperatures cool
slightly from the upper teens (Sunday night) to the lower teens by
Thursday. GFS MOS guidance has highs back into the 70s at GRR on
Thursday. The surface pattern looks fairly diffuse Tuesday into
Wednesday which will trend towards ridging by Thursday.
Overall the focus of the entire 7 day forecast is on periodic
thunderstorm chances. Some locally heavy rain will be possible,
especially from Sunday into Monday.
&&
.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 127 PM EDT Fri Aug 7 2026
Visible satellite loop shows abundant diurnal cu across the
region. Much of that will dissipate toward sunset. High pressure
overhead means light winds tonight, which will help in some fog
formation toward morning. The fog and lower ceilings won`t last
more than a few hours, however, as the high will drift east and
southwest to west winds will increase to 10 to 20 knots.
It`s still possible we could see an isolated shower or storm
develop late this afternoon closer to the eastern terminals, but
that`s far less than certain and was not included in the TAFs.
&&
.MARINE...
Issued at 354 AM EDT Fri Aug 7 2026
For the most part we expect conditions to remain below advisory
levels through the next 3 to 4 days. The first time frame that may
approach advisory levels is tonight when high resolution models
pick up on an increase in the 850mb low level jet to 25-30 knots.
Usually overnight low level jet increases in the heart of the
summer result in building waves. Tonight looks to be no different
with the Wavewatch3 indication 3 to 3.3 foot waves developing. We
will be watching this time frame for any increase in wind and
correspondingly the waves.
The next time frame we will be monitoring will be Sunday when an
increase in southwesterly winds may push conditions to advisory
levels. BUFKIT overviews are showing southwest winds of 15-25
knots which usually pushes waves towards the 4 foot mark.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Dense Fog Advisory until 6 PM EDT this evening for LMZ847>849.
Small Craft Advisory until 11 PM EDT this evening for LMZ849.
&&
$$
DISCUSSION...Duke
AVIATION...04
MARINE...Duke
NWS GRR Office Area Forecast Discussion
