374
FXUS63 KGRR 132338
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
738 PM EDT Wed May 13 2026
.KEY MESSAGES...
- Mainly dry conditions into Friday
- Chances for showers and storms Sunday
- Strong to potentially severe storms on Monday
&&
.DISCUSSION...
Issued at 256 PM EDT Wed May 13 2026
- Mainly dry conditions into Friday
Mainly dry weather is expected through Friday at this point. High
pressure will build in tonight and be located over the region on
Thursday. We will see an erosion of the clouds from west to east
this afternoon and evening. It may take towards midnight or
slightly after until the U.S. 127 corridor scatters the clouds
out. The high slides off to the east Thursday night allowing a
southerly flow to develop for Friday and Saturday. We cannot
cannot rule out some isolated to scattered showers both Friday and
Saturday in a warm air advection regime. Models are not kicking
out significant QPF however with our forecast showing a few
hundredths of precipitation in both Friday and Saturday combined.
- Chances for showers and storms Sunday
Sunday will start out with ridging extending into the forecast
area from the north, an extension of a surface high over
Ontario. As we work through the day however a warm front will
lift in from the south. This is a healthy surge of moisture with
850mb dew points rising from +8C to +14C. The 850mb LLJ in place
pushing this moisture is on the order of 30 knots which is more
than sufficient to produce showers and storms. MUCAPE values via
the GFS and ECMWF are forecast to push towards 1,000 j/kg. Feeling
at this point is severe weather cannot be ruled out, but a better
chances exists on Monday.
- Strong to potentially severe storms on Monday
Better dynamics and stronger wind fields exist on Monday which
should boost the threat for severe weather a bit higher as
compared to Sunday. 45 knot winds at 850mb and a surge of low
level moisture (+14C dew points at 850mb and surface dew points of
almost 70F) should give us a chance for severe weather. The mid
level shortwave in the 12Z runs looks a bit further west which may
trend the threat a little bit to the west as well, but we will be
monitoring the forecast as we move forward.
&&
.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 735 PM EDT Wed May 13 2026
The clearing line has inched eastward through the counties
bordering Lake Michigan, with BKN-OVC MVFR ceilings generally
found farther east/inland. Even a few sprinkles noted on surface
obs (and radar) from LAN south to near JXN area.
As previously discussed, ridge of high pressure will push into
the western Great Lakes tonight and Thursday, and this will allow
skies to clear area-wide overnight (quickly ending sprinkles as
well). VFR conditions /with mainly clear skies/ will develop from
west to east between roughly 01-06Z. Clouds may ultimately be a
bit more stubborn at LAN/JXN. NW breezes will continue to subside
this evening, holding around 10 kt. NW winds of 10-15 kt will
develop again Thursday, along with SCT diurnal CU.
&&
.MARINE...
Issued at 256 PM EDT Wed May 13 2026
We have had some gale gusts as expected today, but we have
trended back down a bit more into Small Craft Advisory territory
as we move through the mid afternoon hours. Northwest winds of 20
to 30 knots are occurring at 200pm. We expected those type of
winds to prevail into the evening hours before winds gradually
begin to settle/diminish into the 10 to 20 knot range for tonight.
The latest WaveWatch3 run matches expectation well with waves
subsiding below 4 feet by 200am. Will therefore let the current
SCA stand as is with an expiration of 200am.
High pressure builds in for Thursday bringing quiescent
conditions. Winds ramp up again for Friday out of the south which
will likely push us back into Small Craft Advisory conditions. The
weekend weather on the big lake looks fairly benign, but we could
be looking at fog developing given higher dew points advecting
over cold lake waters.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 2 AM EDT Thursday for LMZ844>849.
&&
$$
DISCUSSION...Duke
AVIATION...Smith
MARINE...Duke
NWS GRR Office Area Forecast Discussion