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  Monday January 21, 2019

 

NWS Area Forecast Discussion


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FXUS61 KBTV 210838
AFDBTV

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
338 AM EST Mon Jan 21 2019

.SYNOPSIS...
As strong low pressure exits northeast of the region this morning,
lingering light snow is expected to continue across northern
portions of the North Country through much of today, with additional
light accumulations expected. In addition, arctic air filtering into
the region ahead of approaching high pressure will provide
dangerously cold wind chills of 20 to 35 below through the day as
well. Fair and dry conditions are expected on Tuesday, with highs in
the teens and lighter winds, before developing southerly winds ahead
of an approaching upper level disturbance from the Great Lakes
brings our next chance for precipitation on Wednesday.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 338 AM EST Monday...Surface low pressure which brought a major
winter storm to the region yesterday continues to track northeast
into the Canadian Maritimes this morning but the parent upper level
circulations are still moving through the region producing very
light snow across northern portions of the forecast area. 700mb low
to our east this morning continues to provide wrap-around moisture
to the low levels and combined with the 500mb trough passage this
afternoon will continue to provide light snow through much of the
day until drier air works in this afternoon and evening as surface
high pressure begins to build in from the west. Arctic airmass
associated with this high is already building in at the low levels
with surface temps across the region already in the single digits to
teens below zero combining with moderate northwesterly winds to
cause wind chills in the 20-35 below range. Surface temps don`t warm
too much today under strong cold air advection with highs struggling
to hit zero. Winds will only get stronger as the day wears on as the
pressure gradient between the departing low and approaching high
tightens, so wind chill headlines continue into this afternoon and
will likely need to be extended into tonight.

For tonight into Tuesday fair conditions are expected as the
aforementioned surface high and upper level ridge crest over the
region. The combination of fresh snowpack and clear skies will be
favorable for excellent radiational cooling with likely the coldest
night of the winter for most locations. Winds gradually slacken as
the high builds in, but expect enough wind to persist to support
wind chills in the 15-25 below range to continue headlines. Lows
will be widespread int the single digits to teens below zero with 20-
30 below likely across the Adirondacks. Light southerly return flow
develops Tuesday as the high shifts over the eastern seaboard
allowing temps to rebound into the single digits and teens above
zero in the afternoon.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
As of 305 AM EST Monday...The short term starts out quiet on
Tues Night with warming temps overnight and developing southerly
winds. Developing 925mb jet of 35 to 45 knots with aligned
channeling up the slv/cpv will create areas of blowing snow
overnight into Weds. Have placed localized gusts up to 25 to 35
knots, with highest values over near Lake Champlain. Otherwise,
temps continue to warm thru the teens and into the 20s to near
freezing overnight. Coldest values east of the Greens. On Weds
expect a period of snow showers to lift from southwest to
northeast across our cwa. A general dusting to 3 inches
anticipated with highest amounts in the dacks and
northern/central Green mtns. Strong 925mb to 850mb southwest jet
of 45 to 55 knots by 18z Weds will result in some downslope
shadowing in the cpv. Progged 925mb to 850mb temps approach 0c
by 00z Thurs, supporting mainly 30s, but some cooler values in
the upper 20s likely east of the Greens.

By Weds night into Thurs morning still a large degree of
uncertainty on potential development of wave along boundary and
potential for additional precip. In addition, low level thermal
gradient tighten from west to east, making precip type
challenging. The CMC/ECMWF show most of our cwa well established
in the warm sector with 850mb temps btwn 2-4c with brisk
southwest flow paralleling approaching front. This would support
additional qpf in the 0.25 to 0.50 range with highest values in
our central/eastern cwa. Given very cold sfc temps, would expect
areas of freezing rain, especially east of the Greens.
Meanwhile, gfs shows a much more progress system with developing
westerly flow quickly sweeping boundary east, with limited
lingering moisture Weds night into Thurs. This would also
support developing low level caa quickly and a change back to
mostly snow. Given uncertainty continue to mention high chc to
likely pops overnight with temps holding mainly in the 30s,
except upper 20s east of the Greens. Will continue to mention
rain/snow based on sfc temps, but some wintry mix is likely
needed in the upcoming days.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 305 AM EST Monday...The aforementioned boundary is
eventually moving thru our cwa by 00z Friday and precip will end
with a brief period of light accumulating snowfall. Given the
uncertainty on timing of boundary and sfc development have kept
temps mainly in the 30s on Thurs with mention of rain/snow based
on sfc temps. Have noted ecebtv is showing high of 44f, while
mexbtv is 38f, highlighting the uncertainty. Drier and cooler
air returns on modest low level caa Thurs night with some
lingering upslope snow showers. Temps drop back into the teens
and 20s with brisk west/northwest winds.

More uncertainty develops with secondary surge of potential
arctic air on Saturday, with latest 00z GFS much more aggressive
with low level caa. For example gfs shows 925mb temps near -32c
by 12z Sat, while ecmwf is -20c over northern NY. In addition,
gfs shows potent 5h energy with sharp sfc convergence and ribbon
of deeper moisture moving across our cwa Fri Night/Sat, with
the potential for embedded snow squalls, while ecmwf is much
less amplified. Have continue to mention high chc pops for now
with a blend for temps, which supports mostly below normal
values for the upcoming weekend.

Overall pattern does become more interesting again late Sunday
into early the following weekend, as large scale trof with
numerous embedded pieces of energy deepens over the
central/eastern Conus. Meanwhile, as trof amplification occurs
developing mid/upper level ridge builds over the western Conus
and with another ridge over the northern Atlantic. Timing of
individual s/w`s in highly amplified patterns is difficult but
model consensus shows southern stream energy enhancing sfc low
pres over the se conus around hour 160. The uncertainty develops
does the low pres make the turn and come up the coast for
potential impact on our cwa, or slide out to sea. I did notice
almost half the gfs ensemble members show a significant system
with impacts across our cwa, while the 00z ecmwf ensemble mean
has center of low pres very close to Cape Cod. In addition, this
idea is supported by the 00z operational runs of the CMC and
ECMWF. Still many days away and plenty of time to watch
mid/upper lvl trof evolution and associated sfc low pres track,
for potential impacts.

&&

.AVIATION /09Z MONDAY THROUGH FRIDAY/...
Through 06Z Tuesday...Mix of VFR/MVFR will continue through the
overnight hours, with brief reductions in vsby to IFR in
light snow possible. Very light snow will remain persistent at
northern terminals through mid-day Monday then rapidly decrease
in coverage after 18Z with skies scattering to FEW-SCT VFR by
00Z. Winds will remain brisk out of the north/northwest from
8-12 kts overnight, and increase to 12-15kts after 12Z with
gusts 20-25 kts through the remainder of the period.

Outlook...

Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. Slight chance SHSN.
Wednesday: Mainly VFR, with areas MVFR and IFR possible. Likely
SHSN.
Wednesday Night: Mainly MVFR, with areas IFR possible. Likely
SHSN, Likely SHRA.
Thursday: Mainly IFR, with areas MVFR possible. Likely SHSN,
Likely SHRA.
Thursday Night: Mainly MVFR, with areas VFR possible. Chance
SHSN.
Friday: Mainly VFR, with local MVFR possible. Chance SHSN.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Wind Chill Warning until 1 PM EST this afternoon for
     VTZ001>012-016>019.
NY...Wind Chill Warning until 1 PM EST this afternoon for
     NYZ026>031-034-035-087.

&&

$$
SYNOPSIS...Lahiff
NEAR TERM...Lahiff
SHORT TERM...Taber
LONG TERM...Taber
AVIATION...Lahiff


 
 
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