826
FXUS63 KGRR 232349
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
649 PM EST Sat Nov 23 2024

.KEY MESSAGES...

- Potential for drizzle/sprinkles into Sunday

- Rain to Light Snow Monday into Tuesday

- Colder And Potential Winter Weather For The Holiday Weekend

&&

.DISCUSSION...
Issued at 218 PM EST Sat Nov 23 2024

- Potential for drizzle/sprinkles into Sunday

Low level moisture remains abundant during this period. Low level
convergence is shown to increase near and south of I96 tonight
and into Sunday morning. Given the forecasted moisture and lift,
we could see some light precipitation.  The probabilities of
seeing measurable precipitation by the ensemble guidance remains
under 30 percent in this area and we will keep our POPs that way.
We will go with drizzle given this setup. With it remaining
cloudy, the probability to see below freezing temperatures is low
in the drizzle area. Ensemble temperature guidance for Grand
Rapids and Lansing is keeping minimum temperatures in the mid to
upper 30`s for overnight lows. Thus we will not feature any
freezing drizzle.

- Rain to Light Snow Monday into Tuesday

Our first round of notable precipitation in the extended forecast
arrives Monday into Tuesday as a vorticity maxima swings through and
drives a surface low across the state. Ahead of this low Monday,
warm advection brings the potential for highs in the 50s. Our first
shot of colder air arrives behind the low causing rain to change
over to snow Monday Night. As 850mb temps crash to around -5C there
will be some lake enhancement on the back side of this system. QPF
wise we`re looking at under 1/4" of rain with under 1/2" of light
snow. Surface ridging and dry air arrive from the west during the
day Tuesday cutting off our precipitation chances.


- Colder And Potential Winter Weather For The Holiday Weekend

Confidence is high in colder conditions arriving late next week as
longwave troughing sends several reinforcing shots of modified
arctic air into the region. 850mb temps fall to -10C or colder by
the weekend, translating into highs near or below freezing by next
weekend.

What is also likely is that the very cold air aloft with our still
warm lakes will fuel periods of accumulating lake effect snow,
especially later Thursday into the weekend. These bursts of lake
effect snow may cause travel issues, which given the holiday traffic
will need to be monitored closely.

What is less certain is snow on Thanksgiving itself. Solid ensemble
consensus exists that a vorticity maxima on the leading edge of our
troughing causes a low to develop over the southern United States
and eject into the Ohio Valley. Ensemble cluster analysis suggests
that how this occurs is dependent on the extent of troughing and its
interaction with ridging over the Atlantic Seaboard. The trend in
12z guidance is a more northerly low track which brings the
potential for synoptic snowfall on Thanksgiving. The EPS contains
the most aggressive solutions in some members with a track that
brings several inches of snow to the I94 corridor, however this is a
minority of potential outcomes at this point. Chances of snow
exceeding 1" on thanksgiving range from near 15% near US10 to 30-40
percent near I94. Overall, significant snow is unlikely at present,
but trends will need to be watched to see if the northward shift and
associated chance of better snowfall continues.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 650 PM EST Sat Nov 23 2024

MVFR cigs will continue overnight into Sunday morning. There
remains a slight chance for drizzle at the southern TAF sites
though not enough to put in the TAFs. IFR cigs will be possible
Sunday morning, mainly between 09Z at 15Z. Expect conditions to
improve mid to late morning to MVFR and then to VFR after 19Z.


&&

.MARINE...
Issued at 218 PM EST Sat Nov 23 2024

The pressure gradient remains relatively weak through tonight as
a surface ridge gradually builds in from the west. This will
support winds and waves remaining low in the nearshore zones. A
wave of low pressure moves in from the southwest Monday. This will
allow for increasing winds and waves which may reach small craft
advisory levels. Ensemble wind gusts from the lakeshore support
this potential.

&&

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

&&

$$

DISCUSSION...MJS/Thomas
AVIATION...Ceru
MARINE...MJS/CAS