891
FXUS63 KGRR 221134
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
634 AM EST Fri Nov 22 2024

.KEY MESSAGES...

- Lingering light precipitation through tonight

- Potential for showers Monday into Tuesday

- Turning colder with winter weather possible during the holiday
weekend

&&

.DISCUSSION...
Issued at 340 AM EST Fri Nov 22 2024

- Lingering light precipitation through tonight

A large upper-level low will keep lumbering slowly east today, as
the next iteration of surface cyclogenesis along a frontal triple
point occurs over the New York region. Over our area, 500 mb
heights will be rising and 850 mb temperatures warming, and the
midlevels including the DGZ will dry out. Precipitation production
will become more limited to just lake effect in the zones favored
amidst northwest winds. Even then, a strengthening inversion
serving as the lake-effect PBL convective cap around 5 to 7 kft,
as cold as -5 Celsius, will limit showers to mostly light and low-
topped. Most areas are expected to receive very light rain totals
from this point forward, though the HRRR suggests 0.25 inch around
South Haven where a dominant band may come ashore.

- Potential for showers Monday into Tuesday

Within a somewhat more zonal pattern early next week, an upper
level trough is expected to sharpen up as it traverses the
Northern Plains to Great Lakes. The air on the front end of the
surface low that will advect toward Michigan will be rather mild,
and Monday is likely to be the warmest day of the week. Most
members within the global ensembles point to 0.10 to 0.25 inch
QPF, with some outliers around 0.50 if the low deepens sooner, as
the GFS shows a small amount of midlevel instability that may
boost precip rates in that scenario. Any lingering precip on
Tuesday would switch to light, lake-enhanced snow.

- Turning colder with winter weather possible during the holiday
weekend

Ensembles continue to favor colder-than-normal temperatures from
Wednesday onward through the long holiday weekend, with longwave
troughing across southern Canada poised to let modified Arctic air
spill into the Midwest. However, there are differing solutions
regarding the magnitude of troughing into the south-central CONUS,
with implications on the strength and track of a potential low-
pressure system that could provide snow either to Michigan or
farther south in the Ohio river valley to Northeast US around
Thursday-Friday. Regardless of that potential, there is decent
confidence in a pattern that supports accumulating lake-effect
snow and some travel headaches during the long holiday weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 634 AM EST Fri Nov 22 2024

Most sites are starting off this forecast period in the VFR
category. This will be short lived as we see some MVFR ceilings
already working into KAZO and KBTL, and the rest of the area will
see these ceilings also within the first 1 to 3 hours of this
forecast set. The most likely scenario is that all of the
terminals settle in with ceilings in the 1-2k ft agl range. Can
not rule out some IFR, but that is not likely enough at this time
to include in the forecast.

The ceilings will dominate through the period then. The only real
change in the forecast will be winds becoming gusty by late
morning, and then winds diminishing prior to midnight tonight.

&&

.MARINE...
Issued at 340 AM EST Fri Nov 22 2024

Low pressure is reconsolidating over the Northeast US today, and
the air flow around it will lead to winds becoming more uniformly
from the northwest. High pressure nudging into the Midwest will
help maintain a tight pressure gradient and keep wind speeds
blustery and hazardous to small craft. A few gusts to gale force
are possible during the day. Waves will remain hazardous to small
craft through part of Saturday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory until 1 PM EST Saturday for LMZ844>849.

&&

$$

DISCUSSION...CAS
AVIATION...NJJ
MARINE...CAS