557
FXUS63 KGRR 091741
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
141 PM EDT Wed Sep 9 2026
.KEY MESSAGES...
- Showers and isolated thunder today
- Small chance of weekend showers
- Higher chance of showers/storms Monday
&&
.DISCUSSION...
Issued at 248 AM EDT Wed Sep 9 2026
- Showers and isolated thunder today
Not much change to the going forecast. Radar shows light showers
moving east across Lower MI and extending west to Nebraska. Given
MUCAPE only around 100 j/k, it`s no surprise there isn`t much
lightning around. However, HRRR shows SBCAPE increasing to several
hundred j/kg by this afternoon and so isolated thunder remains a
possibility. Current shear values are around 20kts but progd to
increase to 40-50 kts this afternoon. Thus, a few showers or
isolated thunderstorms may be able to produce some gusty winds,
but instability remains lacking. Moisture isn`t though. PWATs
remain high...aoa 2 inches and so locally heavy rainfall remains
possible. Once the cold front moves through after 18z, we`ll see
the showers move southeast with it. Skies will clear late in the
day.
- Small chance of weekend showers
High pressure will create a couple of dry days tomorrow and Friday
before the next cold front moves through. Not a lot of change
there either. It`s a weak front with not much of a thermal
gradient and the accompanying low will be near James Bay. Moisture
return ahead of it is anemic and so PoPs remain low; much of the
weekend will be dry. Highs will be in the upper 70s to around 80,
but dewpoints will remain in the mid to upper 60s creating humid
conditions.
- Higher chance of showers/storms Monday
A strong short wave moving onshore over the Pacific NW will move
east this weekend creating a northern Plains low that will drag a
cold front across Lower MI early next week. this short wave is
progd to be fairly potent and so showers and thunderstorms will be
in the forecast Monday into Tuesday.
Models show a 50kt LLJ Monday afternoon coupled with PWATs aoa 2
inches and 40-50kts of shear along with SBCAPE around 1200 j/kg.
Those are decent dynamics for storm development and we`ll continue
to keep an eye on this potential development.
&&
.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 141 PM EDT Wed Sep 9 2026
Generally light rain this afternoon with ceilings dipping MVFR if
they haven`t already, perhaps temporary IFR. The potential for
additional convection developing this afternoon along the back
edge of the rain is low but still a possibility as models indicate
lingering instability, though limited sunshine and daytime heating
today is keeping the confidence for thunderstorms too low to
include in the TAFs at this time. Medium confidence for patchy fog
early Thursday morning especially in southern Michigan, given wet
ground, light winds, and partially clear skies.
&&
.MARINE...
Issued at 248 AM EDT Wed Sep 9 2026
We`re continuing with the small craft advisory and including all
zones from St Joe to Manistee. While waves wont` be particularly
high south of Holland, winds will increase to 15 to 25 knots this
morning which will make for hazardous conditions. No change to the
ending time of the advisory.
Another small craft advisory may be needed Saturday as another
cold front moves through the region.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 8 PM EDT this evening for MIZ037-
043-050-056-064-071.
MARINE...Small Craft Advisory until 8 PM EDT this evening for LMZ844>849.
&&
$$
DISCUSSION...04
AVIATION...CAS
MARINE...04
NWS GRR Office Area Forecast Discussion
