512
FXUS61 KBTV 190544
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1244 AM EST Thu Dec 19 2024

.SYNOPSIS...
Snow and rain will result in elevationally dependent
accumulations through tonight. Slippery travel can be expected
this evening in areas of heavier snow; however, overall
accumulations will be only up to 4 inches, with perhaps a few
higher totals over 2000 feet in elevation. Following another
chance of snow showers on Friday, very cold conditions will
settle into the region, featuring below zero temperature
readings in many locations.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 1224 AM EST Thursday...No real changes needed to the
forecast with this update. The steadiest precipitation continues
to exit the region, with some ongoing showers across northern
New York.

Previous Forecast...A modestly strengthening low
pressure system and its associated front to our south will be
responsible for a short period of rain and snow for this
afternoon and evening. Total precipitation amounts look to
average a quarter to a half inch. While no Winter Weather
Advisories are issued due to most populated areas seeing under 4
inches of snowfall, localized higher amounts are possible in
higher elevations of south central Vermont, where mesoscale
banding is favored with periods of heavier precipitation.

The mid-level front that is displaced well to the north of the
low pressure system, and the lift and moisture tied to it, are
already producing banded structures that will create varying
precipitation rates across our region. Precipitation will taper
off from west to east as the surface low passes to our east
near Cape Cod around midnight. Two zones of widespread
precipitation are expected. The main one, occurring now, is tied
to a broad zone of 700 millibar frontogenesis lifting
northeastward into northern New York and the northern half of
Vermont. Snowfall rates will generally be 0.25" to 0.5"/hour,
consistent with light but steady precipitation rates and roughly
10:1 snow to liquid ratios. With temperatures at or slightly
above freezing and warm road temperatures from the surface
heating today, accumulations will be primarily on grassy
surfaces through the early evening. After dark, combination of
slight cooling of surfaces and areas of heavier precipitation
rates could lead to slippery conditions and a special weather
statement may be needed to highlight areas of difficult travel.

As the surface low intensifies this evening, we`ll be watching for
heavier precipitation rates tied to potential weak instability aloft
on the northern flank of stronger frontal forcing in southern
Vermont. There remain good signals for heavy snowfall rates in
excess of 1" per hour at times across portions of Rutland and
Windsor where modeling shows rounds of this favorable forcing in
a narrow axis. However, perhaps Orange and Caledonia counties
see this heavier snow as well through the evening, as mesoscale
bands often are displaced a bit north of where the best forcing
is modeled. This heavier snow is favored to blossom between 7
PM and 9 PM before departing to the east before midnight.

The forecast for wet snow at elevations above 1000 feet is
straightforward. Given relatively warm surface temperatures
near or above freezing along with snow growth temperatures being
largely 10 to 15 thousand feet above ground level, snow
character is favored to be wet and possibly heavy, especially in
higher elevations in south central Vermont. Crucially, because
of these mild surface temperatures and lack of cold air
advection due to southerly flow ahead of another surface trough
to our northwest, only when heavier snow falls will rain change
over to snow in the lower elevations. While the HRRR has proven
a little slow at changing rain to snow in the St. Lawrence
Valley, have leaned towards its depiction of precipitation type
shown in recent run, which has been consistent with itself and
observations today of milder boundary layer conditions in the
Champlain Valley. As such, most of the rain will remain liquid
in this region, with a rain/snow mix in the Winooski Valley and
other low elevations in Vermont, through most of the event. In
the St. Lawrence Valley, the low level air mass was just enough
colder that rain has already mixed with or changed to wet snow
with temperatures in the mid 30s, and these areas look on track
to see mainly snow this evening and accumulations of 1 to 2
inches. Much of Vermont above 1000 feet elevations should see 2
to 4 inches, with lower elevations generally a coating to an
inch, through tonight.

Overnight, the aforementioned trough to our northwest will sweep
eastward and allow winds to turn westerly and increase in speed
as pressures rise fairly quickly and colder air filters in. 850
millibar temperatures look to fall from -4 to -10 degrees
overnight while 700 millibar moisture remains elevated through
most of the night. With only modestly strong winds in the 20 to
25 MPH range in the high terrain, this pattern of blocked flow
supports upslope snow showers and flurries, with light
accumulations in the mountains and western slopes. The
breeziness will help reduce chances of any ice conditions
developing for the morning commute, as the mixing will both keep
temperatures near or above freezing in many areas, but also
help to dry out wet surfaces. During the day on Thursday, we
continue to advertise non-diurnal temperature trends with steady
cold air advection. Temperatures will generally be steady or
fall during the day. Aside from lingering morning snow
showers/flurries, it will be a dry day. A brief bit of clearing
is favored before the next system spreads some high clouds
tomorrow night from the west, with skies becoming overcast
overnight. No precipitation is anticipated through daybreak
Friday.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 354 PM EST Wednesday...The end to the work week will turn
rather cold and calm following a brief weak shortwave. A
clipper system will track out of the Great Lakes into the region
Friday afternoon encountering dry and cold air. Furthermore, a
developing coastal low off New Jersey will take most of the
available moisture with it Friday evening. While no impacts are
expected from the coastal low, remnant scattered snow showers
are forecasted Friday evening through Saturday afternoon. Models
indicate widespread light flurries and snow showers across the
region, with higher elevations seeing better precipitation
chances. Model trends show increasing probabilities of
precipitation in the Northeast Kingdom as compared to previous
runs. With moisture levels low, however, most places will only
see between a 0.25" and 1" of snow, with 1-2" possible in the
St. Lawrence Valley. Temperatures Friday be slightly below
average in the upper 20s across much of the region and teens
near the summits.

Behind the clipper, cold polar air 10-15 degrees below average will
filter into the area Saturday night as high pressure builds in for
the weekend. Below zero temperatures are expected across most of the
Adirondacks and parts of northeast Vermont. The Champlain Valley
will see temperatures in the single digits. Exactly how cold the
region gets will be partially dependent on how much snowfall the
region gets Friday and Saturday, as well as how much cloud cover is
present overnight. Areas with more snowfall will be cooler than
those without due to stronger radiative cooling.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 354 PM EST Wednesday...High pressure will continue to
dominate Sunday and Monday with cold polar air remaining in
place during the overnights. Temperatures will struggle to reach
the mid-teens in the Champlain and St. Lawrence Valley, with
near zero highs in the higher elevations on Sunday. Overnight
temperatures in the Adirondacks will remain below zero with
single digits in the valleys. With the polar air in place over
the weekend, Lake Champlain may experience some steaming as the
lake will be considerably warmer than the air temperature. Some
flurries from the potential added cloud cover in the Champlain
Valley are possible Sunday night.

Many will be traveling for the Christmas holiday Monday and Tuesday,
and while no precipitation is expected Monday, temperatures will
remain on the cold side with highs in the upper-teens in the valleys
and single digits in the mountains Monday. Travel is expected to be
the best Sunday and Monday, as a pair of shortwaves move into the
area Tuesday morning. Models have come into better agreement with
less phasing between the waves, indicating two separate systems
Tuesday and then Wednesday. Precipitation chances increase Tuesday
morning into Tuesday night, and are expected to continue through
Christmas Day.

If you are hoping for a white Christmas, the ingredients are slowly
coming together for some frozen precipitation both Christmas Eve and
Christmas Day. While still uncertain on the exact timing and
intensity of the shortwaves, cool air looks to be in place at the
onset of the event. However, model uncertainty on the temperatures
during the event linger. The GFS indicates some warm advection with
a more positively tilted trough axis, whereas the European indicates
a more broad trough which would keep the cold air in place
throughout the event. How the shortwaves interact will ultimately
determine how much cold air is available and how much precipitation
the region receives. A faster phasing will increase the
precipitation chances, but increase the chance for a rain/snow
mix. However, less phasing, and a faster moving initial
shortwave, will keep the cold air locked in, but lessen the
chances of precipitation on Christmas.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
Through 06Z Friday...Widely variable flight conditions across
the forecast area for the next several hours, ranging from VFR
to LIFR, with most terminals currently experiencing MVFR
ceilings and visibilities as widespread precipitation continues
to exit the region. While most ceilings are generally between
1300 to 3500 ft AGL, there are some areas of IFR ceilings that
have occasionally been impacting terminals, which should
continue to become more scattered as the steadiest precipitation
exits. Precipitation has come to an end, or will end in a few
hours, at most terminals but KSLK and KEFK will continue to have
additional chances for snow showers through the forecast
period. Winds are currently light and variable, becoming more
northwesterly with some gusts possible in the afternoon.

Outlook...

Friday: Mainly VFR, with areas MVFR possible. Chance SHSN.
Friday Night: Mainly MVFR, with areas VFR possible. Chance SHSN.
Saturday: Mainly MVFR, with areas VFR possible. Chance SHSN.
Saturday Night: Mainly VFR, with local MVFR possible. NO SIG WX.
Sunday: VFR. NO SIG WX.
Sunday Night: VFR. NO SIG WX.
Monday: VFR. NO SIG WX.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.

&&

$$
SYNOPSIS...Kutikoff
NEAR TERM...Kremer/Kutikoff
SHORT TERM...Danzig
LONG TERM...Danzig
AVIATION...Kremer