538
FXUS63 KGRR 131040
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
640 AM EDT Tue Oct 13 2026
.KEY MESSAGES...
- Multiple chances of rain into Friday
- Dry and seasonable this weekend into early next week
&&
.DISCUSSION...
Issued at 238 AM EDT Tue Oct 13 2026
- Multiple chances of rain into Friday
The last of the shower activity from the showers and storms that
started moving in last evening are now along U.S.-131 and rapidly
moving east. Once these are gone in the next couple of hours, we
will stay dry until toward midnight tonight. We will see low clouds
on the backside of the low spread across the northern half of the
forecast area late this morning and early this afternoon. They will
then move out by this evening.
The cold front will drop down to just south of the state to about
the I-80 corridor by 00z this evening. It will then slow down for a
bit as we see a short wave eject from the Western long wave trough,
and ride along it. A 30 knot low level jet mainly just south of the
area will force showers to develop over roughly the south half of
the forecast area. Thunder chances tonight look much less likely,
with the sufficient instability present only near the I-94 corridor.
Wednesday looks to be mainly dry as we see upper ridging build over
the area behind the departing system Tuesday night, and the system
organizing to move in here Thursday into Friday.
The Thursday/Friday system will be quite dynamic as we have a strong
northern branch wave diving southeast from Canada, and a wave across
the SW U.S. lifting up to the NE and phasing with the northern
stream system. Strong upward motion will move over the area on
Thursday ahead of the phased long wave trough. An associated 40-50
knot low level jet will help to focus moisture transport over the
area Thursday, bringing better rains to the southern half of the
area once again. Thunder chances once again look limited to the I-94
corridor.
Showers will continue Friday, with the focus of the rain being along
the lakeshore. This will occur as the upper trough moves overhead
briefly. The upper jet core sinks south of the state briefly,
providing for deep colder air and instability over the lake. The
lake is generally sitting around 15-17C and 850 mb temps are
forecast to drop to around 0C Friday afternoon. The better lake
effect rain showers will tend to be earlier. We see the upper jet
core lift NE out of the area by later in the day. This will allow
subsidence to help limit the vertical development of the lake effect
by evening. We will see quite windy conditions with 40 mph gusts
very plausible, especially near the lakeshore.
- Dry and seasonable this weekend into early next week
The upper trough will zip away from the area late Friday, and upper
ridging will be building in quickly by Saturday. This upper ridge
will be slow to move out due to the amplified upper air pattern with
the stronger system just off of the east coast, and the closed off
low to the west.
Eventually this closed off low will weaken, and likely eject to the
NE toward the area sometime early next week. This is likely to be
our next chance of rain after Friday. The timing of it will depend
how quick or slow the upper low is to dampen and move up toward the
area.
&&
.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 640 AM EDT Tue Oct 13 2026
Skies have now cleared out at most of the terminals, except some
patchy clouds around 6k ft agl near KMKG. We do think some low
level moisture will move in late this morning and early this
afternoon behind the cold front and sfc low. This will be mostly
evident at KMKG and maybe at KGRR. These clouds will linger until
like 21-23z.
We will see another possible round of showers over the southern
half of the forecast area. These will become possible after around
04z, and last for a couple of hours. lower clouds are then
expected to move in, especially along the I-94 corridor. MVFR is
likely there.
&&
.MARINE...
Issued at 238 AM EDT Tue Oct 13 2026
We will continue to see Small Craft Advisory conditions persist into
the early afternoon hours when the better gradient on the back side
of the incoming low moves east. Waves coming down will follow their
typical lag behind the winds coming down.
Our next marine headline event looks to begin on Thursday out ahead
of the stronger system moving in over the region. Small Craft
Advisory conditions are likely on the front end, with Gales likely
on Friday on the back side of the system with strong cold air
advection over the warmer lake.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 2 PM EDT this afternoon for
LMZ845>849.
&&
$$
DISCUSSION...NJJ
AVIATION...NJJ
MARINE...NJJ
NWS GRR Office Area Forecast Discussion
