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  Monday January 21, 2019

 

NWS Area Forecast Discussion


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FXUS61 KBTV 210837
AFDBTV

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

.SYNOPSIS...
Strong low pressure will depart across the Gulf of Maine and
into the Canadian Maritimes this evening and overnight. Will see
periods of lingering light snow across the North Country
tonight and into Monday, with additional light accumulations
expected. Also, strengthening north and northwest winds will
result in continued areas of blowing snow, with areas of reduced
visibility and slow travel conditions. With arctic air in place
over the next 24 to 48 hours, dangerously cold wind chills can
be expected areawide, with wind chill values falling to 25 to 40
below tonight through Monday. Fair and dry conditions are
expected on Tuesday, with highs in the teens and lighter winds.
Developing south winds and an approaching upper level disturbance
from the Great Lakes brings our next chance for precipitation on
Wednesday.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 711 PM EST Sunday...The forecast remains in good shape as
of early evening. Other than tweaking sky cover to show some
occasional partial breaks in the overcast and to trend hourly
temps/dewpoints toward most recent observational data no changes
were made. Have a warm and safe evening.

Our major snowstorm is beginning to
wind down this afternoon. The best snowfall rates are departing
east of Vermont this afternoon, as 988mb sfc low shifts ewd
across Cape Cod and into the Gulf of Maine this evening, with
best large-scale forcing and deeper saturated layer exiting
eastward. With lingering low clouds and orographically blocked
flow (Froude #s expected below 0.5 next 24hrs), we can expect
continued periods of light snow across the Champlain Valley into
the mtns of central and nrn VT, which will likely linger into
the day on Monday. Additional accumulations generally expected
in the 1-3" range as we lose better dendrite growth. In addition
to the periods of lighter snowfall, NW winds of 15-25 mph with
gusts as high as 30-35 mph in the Champlain Valley, will cause
considerable blowing and drifting snow tonight into Monday
morning. With these concerns, decided to convert the expiring
Winter Storm Warning to a Winter Weather Advisory through 7 AM
Monday from the Champlain Valley eastward. Snow showers will be
somewhat less likely across nrn NY with drier air mass moving
in from sern Ontario.

Other major concern are the dangerously cold wind chills. Arctic
air filters back into the region on strengthening N-NW winds
this evening, and will see wind chills drop to 20 to 40 below
tonight thru Monday. Kept the Wind Chill Warning going through
1PM Monday...and may ultimately need to extend that a bit later
in time. Lows tonight generally -5F to -15F, with highs on
Monday only -5F to +5F. Diminishing winds and partial clearing
set up a better radiational cooling night for Monday night, with
1039mb sfc anticyclone building in across NY state late. Should
see temperatures drop rapidly late with the fresh snow pack and
some clearing. Lows Monday night expected between -8F at BTV and
generally -10F to -20F elsewhere. Locally down to -23F or colder
at KSLK.

Please see our Local Storm Reports and Public Information
Statements for observed snow totals across the region as we
receive them.

&&

.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 /08Z 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...Banacos/JMG
NEAR TERM...Banacos
SHORT TERM...Taber
LONG TERM...Taber
AVIATION...Lahiff


 
 
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