855
FXUS63 KGRR 121840
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
240 PM EDT Tue May 12 2026
.KEY MESSAGES...
- Showers and a few thunderstorms this evening
- Small chance for showers on Friday
- Higher chances for showers/storms Saturday night through Tuesday
&&
.DISCUSSION...
Issued at 240 PM EDT Tue May 12 2026
- Showers and a few thunderstorms this evening
A cold front associated with a clipper system will sweep through
the area this evening and tonight. The front should clear the
forecast by 600am on Wednesday. Forcing and instability should
combine to produce a few thunderstorms during the 700pm to 200am
time frame. Given the presentation of 4hr reflectivity in the
HREF, storms should be isolated/scattered at best. This makes
sense given marginal moisture in place at the surface. 50-55F dew
points surge in from the southwest ahead of the front. The
marginal moisture results in low MUCAPE values at 500 j/kg or
less. Where frontal lift combines with MUCAPE values around 500
will be the locations that a few storms develop. If low level
moisture overperforms a bit, we could see some small hail or gusty
winds to around 40 mph. We get back to dry weather for Wednesday
and Thursday.
- Small chance for showers on Friday
There is a chance for showers that exists on Friday associated
with a weakening cold front pressing in from the west. We are
carrying 20-40 percent chances for light rain showers across
Western Lower Michigan on Friday with dry weather in the east.
Some light pops are possible in all areas Friday night. The driver
of the precipitation other than the weakening cold front are some
embedded shortwaves in zonal flow. Overall what occurs will be on
the light side.
- Higher chances for showers/storms Saturday night through Tuesday
We move into a more active pattern later in the weekend into early
next week. Deep southwest flow develops with a couple of systems
in play through the Sunday through Tuesday period. A warm front
lifts into the area from the southwest on Sunday. We break into
the warm sector Sunday night into Monday before a cold front
sweeps through Monday night. We will have much deeper moisture in
the area during this time frame with surface dew points pushing
into the 60s. PWAT values rise to around 1.6 inches which is near
daily max values looking at climatology. Sunday and Monday look to
be the better chances for convection that may trend towards severe
given the combination of moisture and stronger LLJ winds.
&&
.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 210 PM EDT Tue May 12 2026
Scattered showers and thunderstorms will impact West Michigan TAF
sites this afternoon through this evening. Ceiling/visibility
restrictions should limited, however, with only pockets of
temporary MVFR vsbys expected in the heavier showers. Thunderstorm
chances at any TAF site should be confined to a 3-4 hr window
that gradually transitions from west to east between 22Z and 05Z.
Severe storms are not expected at this time.
Winds will increase from the S/SW late this afternoon with gusts
in excess of 25 kt. Winds will become W tonight and eventually NW
Wednesday, with gusts of 25-30 kt expected. Have retained LLWS at
the AZO/BTL/JXN TAF sites tonight along and just in advance of
approaching cold front.
&&
.MARINE...
Issued at 240 PM EDT Tue May 12 2026
A clipper system moving through the Great Lakes region today and
tonight will bring Lake Michigan stronger south winds today which
veer to the northwest tonight. South to southwest winds this
afternoon and evening will reach the 20-30 knot range with a few
gale force gusts at times. We are thinking the gale gusts will not
be persistent enough for an upgrade to a Gale Warning. Winds
shift to the northwest after midnight with a similar setup...20-30
knots with a chance for gale force gusts. We will be monitoring
both time frames, but will continue with the Small Craft Advisory
for now for today and tonight. Winds and waves will decrease to
below advisory levels Wednesday night. Will hold off on extending
the SCA for now through Wednesday just to make sure we do not
need to upgrade. Later shifts will make that decision.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 8 AM EDT Wednesday for LMZ844>849.
&&
$$
DISCUSSION...Duke
AVIATION...Smith
MARINE...Duke
NWS GRR Office Area Forecast Discussion
