Glenn, Michigan Weather Forecast Discussion

042
FXUS63 KGRR 221900
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
300 PM EDT Mon Sep 22 2025
.KEY MESSAGES...
- Scattered Showers/Storms Much of This Week
- Dry Weather Likely for the Weekend
&&
.DISCUSSION...
Issued at 300 PM EDT Mon Sep 22 2025
- Scattered Showers/Storms Much of This Week
An upper trough located across WI into the U.P. this afternoon
will slowly move east into tomorrow before slowing down and
closing off as an upper low directly overhead the region
Wednesday into Thursday. What this will lead to is pretty
extensive cloud cover for a few days but also scattered, mainly
diurnally driven showers and thunderstorms across the Lower
Peninsula.
For tonight, a weak LLJ initially oriented SW to NE will start
angling more eastward and then southeastward across the region,
perhaps touching off scattered showers/storms overnight near and
east of where today`s convective activity developed (which was
over Lake Michigan into west central Lower MI). This scenario is
favored by most CAMs. Currently the most likely region to receive
some rain tonight is near and north of I-96, though given timing
and location differences by the CAMs most probabilities are
30-50%.
Tuesday doesn`t look much different than today in terms of morning
low cloud cover and scattered diurnal showers and a few storms
developing. Widespread rain is not expected. For Wednesday, given
the upper low placement overhead we`ll see 850 mb winds converge
across the eastern half of the region as PWAT values likely reach
their peak for this event, getting close to 1.50" which is about
175% of normal for late September. What this equates to is
whatever showers and thunderstorms do develop, they could be heavy
rain producers with slow storm motions. Certainly wouldn`t be
surprised to see areas especially near and east of US 131 pick up
an additional inch or more of rain. The upper low takes its sweet
time moving out on Thursday so we can`t drop rain chances until
that exits the region.
- Dry Weather Likely for the Weekend
Good ensemble agreement exists on a dry weekend. Upper heights
build into Friday, and upper troughing is expected to stay
primarily north of the state on Saturday as heights resume
building into Sunday. Looks like a fair amount of sunshine as
well, along with light winds. Highs should reach the mid to upper
70s.
&&
.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 157 PM EDT Mon Sep 22 2025
Ceilings have recovered above IFR but a broken MVFR cloud deck is
still prevalent across some of the terminals. Scattered showers
and thunderstorms have been moving over Lake Michigan and a few
pop up showers and isolated storms have been occurring over land.
PROB30 groups are currently the best way to handle this threat
into the afternoon and evening given the weak nature of the
convection and overall coverage expected. Lowering visibilities
are likely later tonight (especially after 06z) and additional
showers with a few thunderstorms are possible as well, though
location is difficult to determine at this point.
&&
.MARINE...
Issued at 300 PM EDT Mon Sep 22 2025
Fairly tranquil conditions expected on the lake this week with
light winds expected and as a result, little in the way of wave
activity. The highest waves will likely occur on Thursday south of
the Holland area with some 2 to 3 footers possible.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...Hoving
AVIATION...Hoving
MARINE...Hoving

NWS GRR Office Area Forecast Discussion