118
FXUS63 KGRR 230244
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
944 PM EST Fri Nov 22 2024

.KEY MESSAGES...

- Light lake-effect showers this evening

- Showers Monday and Tuesday

- Colder Weather and Potential Winter Weather For The Holiday Weekend

&&

.UPDATE...
Issued at 944 PM EST Fri Nov 22 2024

The Great Lakes sit between low pressure centered in the Middle
Atlantic states to the east and high pressure situated from the
Plains northwest into the Yukon and Northwest Territories of
Canada. A northwest flow sweeps across the Great Lakes between
these two features resulting in plenty of clouds and occasional
rain showers downwind of the lakes this evening.

Specifically in Western Lower Michigan, enough low level
instability is in place over Lake Michigan to produce rain
showers. Delta T`s are in the lower teens C with lake water temps
near +12C and 850mb temps near -2C. Not much changes to the level
of instability overnight, so the clouds will at least continue. We
expect precipitation to dwindle and end though before daybreak as
upper cyclonic flow is replaced by ridging which slowly builds in
from the west. So, very light rain showers tapering off is the
expectation near the lakeshore. Mostly cloudy skies should
prevail, but would not be surprised to see a few breaks develop
inland away from the lake. Lows tonight should be a few degrees
either side of 40.

&&

.DISCUSSION...
Issued at 337 PM EST Fri Nov 22 2024

- Light lake-effect showers this evening

Cyclonic flow, residual moisture and marginal lake to 850 mb
delta Ts will bring rather light rain showers this evening across
the western zones. The showers diminish late tonight as inversion
heights lower and moisture becomes more shallow.

- Showers Monday and Tuesday

Our next significant chance of precipitation arrives Monday and
continues into Tuesday as a upper-level trough crosses into the
Great Lakes. Warm air advection ahead of this trough sends highs
into the lower 50s before a cold frontal passage marks the start of
our next cooldown. The rain looks to be in two waves. The first will
be with a weak leading wave followed by the secondary wave and
associated cold frontal passage. Rain looks to be light, generally
under 0.25 inches. Much colder air will provide lake enhancement to
precipitation on the back side of the developing low to our east in
this timeframe. This precipitation will mix with or switch to snow
as we dry out.

- Colder Weather and Potential Winter Weather For The Holiday Weekend

Confidence is high in much colder air infiltrating the area late
next week bringing our first true taste of winter. Longwave
troughing from Canada diving south brings a modified arctic air mass
across the Great Lakes region sending 850mb temps plummeting to near
-10C. Cluster analysis shows that questions on both the magnitude of
this troughing, as well as potential interaction with downstream
ridging exist. This could develop a low pressure system over the
southern United States that brings synoptic snowfall to the upper
Great Lakes or the northeastern United States, however specifics in
this pattern remain limited at this time. Regardless of any synoptic
potential, the modified arctic air over our still very warm lakes
and overall longwave pattern are supportive to the potential for
lake effect snow in the latter part of next week. Given the upcoming
thanksgiving holiday and associated travel this will need to be
monitored.

&&

.AVIATION /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 740 PM EST Fri Nov 22 2024

MVFR cigs continue to dominate and will continue to do so through
the TAF period. Expect light rain this evening to slowly taper off
by 04Z. Gusty west to northwest winds will continue until around
06Z though some winds could continue to filter down towards
morning. Gusty winds will return tomorrow afternoon.

&&

.MARINE...
Issued at 337 PM EST Fri Nov 22 2024

No changes to the SCA. After a brief lull late Saturday into
Sunday, winds and waves will increase again early next week.

&&

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

&&

$$

UPDATE...Duke
DISCUSSION...Ostuno/Thomas
AVIATION...Ceru
MARINE...Ostuno