150
FXUS63 KGRR 260140
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
940 PM EDT Wed Sep 25 2024

.KEY MESSAGES...

- Small rain chances Saturday through Tuesday

- Drier and cooler mid-week next week

&&

.UPDATE...
Issued at 940 PM EDT Wed Sep 25 2024

Added patchy fog into the forecast for late tonight / early Thu
morning for parts of the area. Consensus of short-term models is
leaning toward the better chance of fog being west of US-131,
where already the Ludington and South Haven AWOSes are reporting
dips in visibility. The forecast thermodynamic soundings in the
HRRR and ARW do not seem as robust for fog as they were a few
times last week, but it will be close in spots, enough for shallow
fog patches, as forecast min temps should drop a couple degrees
below the crossover temperature.

&&

.DISCUSSION...
Issued at 258 PM EDT Wed Sep 25 2024

- Small rain chances Saturday through Tuesday

Fair weather with drier air arriving overnight through Thursday.
Confidence is increasing that we will remain dry for Friday, and
see small chances for rain showers beginning Friday night and
lasting into Tuesday.

Many of the various models and ensemble members continue to show
what is left from "Helene" will be absorbed by the Upper Low
centered near AR/TN/MS on Friday. The strength of the upper high
over our area and the upper low will wrap it back to the NW, but
keep most of the system south of the area.

What we will see from this scenario is we will see moisture advect
in from the SE, and weak short waves rotating on the northern flank
of the combined upper low complex. Much of the period from Saturday
through Monday will be dry. There will be periods when short waves
move through, combined with diurnal instability that will fire off a
few showers and even isolated storms at times. The air with this
system will not be that cold with the tropical part of this.

- Drier and cooler mid-week next week

Eventually what will happen by Monday night/Tuesday is we will see a
strong upper jet and associated upper wave dive toward the area.
This is a strong enough system that it will boot the weekend upper
low out. This system will arrive with a strong cold front, and a
chance of showers and storms. The flow ahead of the front will not
be favorable for much rain with the front.

The front is forecast to move through at some point on Tuesday. The
frontal passage looks to end rain chances at that point, and it will
cool the air down markedly as 850 mb temps drop from the low/mid
teens C, to the lower single digits C by Wednesday. This will
support highs in the 60s and lows in the 40s.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 746 PM EDT Wed Sep 25 2024

VFR expected to be prevalent tonight and Thursday although cannot
rule out some MVFR or lower vsbys in fog late tonight and early
Thursday (mainly between 08Z and 13Z). Given the low confidence in
overnight fog formation/coverage, have maintained the earlier
strategy from the 18Z TAFs of carrying a 4-5 hr period of VCFG in
most of the TAFs.

&&

.MARINE...
Issued at 258 PM EDT Wed Sep 25 2024

Winds are expected to remain below 20 knots and waves below 3 feet
into the weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...None.

&&

$$

UPDATE...CAS
DISCUSSION...Ostuno/NJJ
AVIATION...Meade
MARINE...Ostuno