407
FXUS63 KGRR 250810
AFDGRR

Area Forecast Discussion National Weather Service Grand Rapids MI
309 AM EST Mon Nov 25 2024

.KEY MESSAGES...

- Periods of showers into early Tuesday

- Light rain and snow Wednesday into Thanksgiving Day

- Colder with lake effect snow showers Friday and beyond

&&

.DISCUSSION...
Issued at 309 AM EST Mon Nov 25 2024

- Periods of showers into early Tuesday

We had the first round of light showers pass through last evening
associated with the nose of a low level jet and leading edge of
better moisture transport. This band is in the process of moving out
of our forecast area to the NE as of 2:30 am/0730z, with just some
patchy light showers centered roughly near I-96.

We are expecting multiple periods of showers to continue for today
and tonight with multiple upper waves poised to move through the
area. The first of which is over IA early this morning, will arrive
by 12z. This will prolong the low level jet pumping moisture into
the area this morning, and provide some weak instability for a few
more showers to develop. Then the main wave will arrive toward dark
this evening, providing more showers with better moisture to work
with by then. This will then sweep most everything out by 12z
Tuesday.

Some light precipitation in the form of light rain or snow could
continue into Tuesday along the U.S.-10 corridor as additional upper
energy will be affecting mainly Northern Lower.

- Light rain and snow Wednesday into Thanksgiving Day

We should see a lull in the precipitation for most of the area
Tuesday into early Wednesday before some light rain/snow chances
arrive for Southern Lower.

Some light precipitation in the form of light rain or snow could
continue into Tuesday along the U.S.-10 corridor as additional upper
energy will be affecting mainly Northern Lower. The rest of the area
will be seeing ridging building in between the departing wave from
today, and the next wave coming in later Wednesday. It will be
noticeably cooler on Tuesday with temperatures likely falling
through the day as the colder air arrives.

The light precipitation coming in Wednesday will be associated with
the next wave that will see phasing from a wave coming in from
Canada and another that is currently the low offshore of the Pacific
NW. This will support sfc low development that will travel now just
south of the Ohio River Valley. The far southern rows of counties
will be on the far northern periphery of the precipitation shield
with this system centered on Wednesday night.

Snow amounts and related impacts (especially with Wednesday being a
high volume travel day) remain a little uncertain still at this
time. The general consensus is that most of the snow with this
system will be centered across Northern Indiana and Ohio. However
there are still a few ensemble members that have the track a little
further north, and dump a little bit more snow for our southern two
rows of counties. Drier air on the northern edge of the
precipitation shield should reduce the amounts a bit.

The good news is that most of it will happen after dark, and
hopefully after many are done traveling for the holiday. We will
continue to fine tune the forecast with the latest trends. It does
look like most of the holiday itself will be quiet and cool as short
wave ridging builds in for the daylight hours.

- Colder with lake effect snow showers Thu night and beyond

The break on Thanksgiving Day itself will be short lived, as another
stronger short wave arrives Thursday night and into Friday. This
scenario will have the upper jet core dropping south of the area,
and allowing the deep colder air and cyclonic flow to become
entrenched over the area. 850 mb temps are expected to drop to
between -11 and -13C, providing for more than sufficient instability
over the lake with delta t`s in the 20`s C. The dominant flow
pattern looks like it will be from the WNW. This will favor all of
the lakeshore, and most of the SW quadrant of the forecast area.
These areas are likely to see advisory type snows Thursday night
into Friday night.

We should see a break in the lake effect intensity centered around
Saturday, as the models are showing that we see some short wave
ridging build in. The upper jet core retreats temporarily north of
the area. This will be short lived as yet another short wave drops
down Saturday night, that will bring the jet back south of the area.
We should see the lake effect ramp up at that time, and continue at
least through next Sunday. The flow looks again to be from the WNW,
but that is likely to change a little being seven days out yet.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 130 AM EST Mon Nov 25 2024

A low pressure system will roll through Lower Michigan today,
bringing light rain showers and deteriorating ceilings and
visibility. A slide into MVFR then IFR is likely through the course
of the morning, and IFR is likely to linger until late this evening
until the low passes by. Temperatures will tumble Monday night, so a
changeover to snow showers is expected after 06Z Tue.

&&

.MARINE...
Issued at 309 AM EST Mon Nov 25 2024

The Small Craft Advisory issued by the day shift looks to be in very
good shape for later today through Tuesday, and will not be changed
at all at this time. Winds ahead of the system are not high enough
to cause impacts being offshore flow and with warmer air moving in.
The best wind and wave action will come behind the system as colder
air and a tight gradient overspread the area. Things should improve
late Tuesday.

We should see some relatively quieter conditions settle in for
Wednesday and early Thursday, before our next event commences later
Thursday and Friday. This will come with another surge of colder air
that will be persistent likely into early next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
MARINE...Small Craft Advisory from 6 PM this evening to 7 PM EST
Tuesday      for LMZ844>849.

&&

$$

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