568
FXUS63 KGRR 070700
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
300 AM EDT Mon Sep 7 2026
.KEY MESSAGES...
- Mostly sunny today, cool tonight
- Chance of showers/storms Tuesday night/Wednesday, weekend
&&
.DISCUSSION...
Issued at 300 AM EDT Mon Sep 7 2026
- Mostly sunny today, cool tonight
High pressure stretching from western Quebec southwest across the
western Lakes will bring another day of tranquil weather with
seasonal highs in the upper 70s, followed by lows in the lower to
mid 50s tonight. The ridge will then begin to drift eastward
tonight.
- Chance of showers/storms Tuesday night/Wednesday, weekend
South winds will increase Tuesday as the surface high moves east
and the upper ridge moves overhead. What we`ll see is an increase
in heat and humidity as temperatures climb into the lower to mid
80s dewpoints rise into the 60s. The upper ridge will be flattened
by a short wave moving across the northern tier of states behind a
surface cold front. The LLJ increases to 40 kts Tuesday night
ahead of the cold front. As precipitable water values increase to
2 inches, we may see some heavy rain develop as convection
develops along/ahead of the front. Latest RRFS progs show
convection developing over the northern half of the cwa after 06z
Wednesday. This is also where the nose of the LLJ is and highest
MUCAPE. It`s worth noting the GFS is not bullish on CAPE Tuesday
night and the RRFS has backed off a bit too. That said, we`ll need
to watch for localized flooding as the upper flow becomes more
parallel to the frontal boundary, which could lead to training
echos.
Given the high PWATs, upper short wave, and approaching cold
front, PoPs in the 90 percent range seem reasonable late Tuesday
night and Wednesday. Once the front moves south Wednesday
afternoon, the precipitation will go with it, leading to a couple
of dry days late in the week. Highs will fall back into the 70s
and dewpoints will retreat to the 50s.
The next cold front will approach Saturday. At this point, models
show the best upper dynamics well north into Canada which may
result in lower PoPs...20-30 percent...late Saturday into Sunday.
&&
.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 109 AM EDT Mon Sep 7 2026
Latest IR loop shows abundant cirrus spilling over the ridge in
place across the Great Lakes. We`ll see those high clouds
throughout the TAF period. It`s possible some shallow fog develops
around sunrise at LAN/JXN this morning, but confidence wasn`t high
enough to include in the TAFs.
&&
.MARINE...
Issued at 300 AM EDT Mon Sep 7 2026
High pressure overhead will result in winds and waves well below
advisory criteria. However, as the high drifts east late tonight,
south winds will begin to increase and a small craft advisory will
likely be needed Tuesday afternoon into potentially Thursday.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.
&&
$$
DISCUSSION...04
AVIATION...04
MARINE...04
NWS GRR Office Area Forecast Discussion
