535
FXUS63 KGRR 311800
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
200 PM EDT Fri Jul 31 2026
.KEY MESSAGES...
- Showers with isolated storms this evening into early Sunday
- Watching the upper low position for Monday and Tuesday
- Another period of rain chances mid week
&&
.DISCUSSION...
Issued at 200 PM EDT Fri Jul 31 2026
- Showers with isolated storms this evening into early Sunday
Upper trough close to closing off near the MN/IA border this
afternoon remains poised to bring a period of rain beginning this
evening, and continuing potentially into early Sunday.
The better rain axis begins just west of the Chicago/Milwaukee areas
early this afternoon. This will take some time and evolve as it
moves toward the area. The system overall is a slow mover as it
closes off aloft. In addition, we have a fair amount of dry air
aloft that will eat away at the leading edge of the precipitation
shield.
In addition, the nose of the 850 mb low level jet is driving a lot
of this initial rain. The way the upper low is moving SE, the
convergence ahead of the low level jet is not impressive over our
area tonight as the better convergence moves south of the area. We
expect rain amounts to be on the lighter side through most of
tonight, but high probabilities moving through the night.
Then on Saturday, we transition from the forcing via the low level
jet, to more the deformation zone of the upper low and resulting mid
level fgen Saturday morning and early afternoon. This actually looks
to be the best potential for rain for most of the area during this
entire event.
The potential for thunder is rather low, but non-zero for tonight
and Saturday morning. The better chance actually looks to be once
the mid level deformation likely moves out, and we see the rain
scatter out a bit, and some heating take place. The cold pool aloft
combined with the diurnal warming will produce enough instability to
pop some showers and isolated storms tomorrow afternoon and early
evening. Some of these could be locally heavy with Precipitable
Water values quite a bit elevated to around 2.0 inches. We are not
expecting event totals to cause any hydrology issues. We could be
looking at some local flood advisories with prolonged heavy
downpours over any one location.
The upper low remains close enough, with the occluded front lifting
northward to SE LOwer then on Sunday. Much of the area should end up
dry on Sunday with a dry flow coming in from the NNW to NNE. The SE
corner of the forecast area is likely to keep some rain chances in
most of Sunday. One thing we have to watch for as is typical with
upper lows, is the exact movement of it. The models don`t typically
nail down the exact track with slight strength differences and short
waves helping to complicate progs.
- Watching the upper low position for Monday and Tuesday
The best thought right now for Monday and Tuesday is that we should
see drier conditions return to all of the area with seasonable
temperatures. We see the large upper ridge over the Western U.S. be
pushed toward the area by Monday and linger through Tuesday.
The caveat to this is dependent on the upper low being pushed out
also. There is a chance that the upper low could be delayed in
moving out. This could happen with the large ridge over the Atlantic
holding up the progression of the low, and/or the upper low could
remain closed and want to hold over the area a bit longer. We will
ride the drier forecast for now, but this will have to be monitored.
- Another period of rain chances mid week
Also dependent on the upper low moving out, will be the next system
that will be trying to move toward the area around mid-week next
week. We see a stronger long wave trough that initially pushes the
ridge toward the area. Then a piece of that trough continues east,
and tries to flatten the ridge a bit. If it does not get blocked
from coming in, it looks to affect the area late Tuesday into early
Thursday. This pattern should keep the area from being affected
strongly by any big heat ridge for now.
&&
.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 132 PM EDT Fri Jul 31 2026
VFR conditions will continue into Saturday morning when rain and
lowering ceilings move in with MVFR conditions expected to prevail
after 12Z. Light and variable winds through the evening then going
easterly on Saturday with gusts over 15 knots at times.
&&
.MARINE...
Issued at 200 PM EDT Fri Jul 31 2026
We are looking at marine headlines (Beach Hazards and Small
Craft Advisories) likely being needed for the Sunday time frame.
We are starting off the weekend with favorable conditions today, as
the water temperature has warmed back up after an upwelling event
earlier this week along with warm and dry conditions. This will
deteriorate as rain moves in this evening, and flow becomes offshore
with the approach of the system. This will push the warmer water
back offshore.
The offshore winds will then increase by Sunday and turn from the
North. This will build the waves into the hazardous category. This
event looks to last into Monday morning before winds, and eventually
waves come down significantly.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...NJJ
AVIATION...Ostuno
MARINE...NJJ
NWS GRR Office Area Forecast Discussion
