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  Monday January 21, 2019

 

NWS Area Forecast Discussion


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376
FXUS61 KBTV 192253
AFDBTV

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
553 PM EST Sat Jan 19 2019

.SYNOPSIS...
A dangerous winter storm is on tap for the North Country
tonight through Sunday as low pressure over the Ohio Valley
tracks to near New York City by Sunday morning, and into the
Gulf of Maine by Sunday evening. Steady snow will develop across
the region through this evening, and become heavy at times
overnight into Sunday morning. Snowfall rates of 1 to 2 inches
per hour are expected, making for hazardous travel. As low
pressure departs to our east across the Gulf of Maine and
Canadian Maritimes, blowing snow will increase throughout the
day Sunday as north winds increase. Frigid temperatures and very
low wind chills are also expected tonight through Monday night,
adding to the hazardous conditions. Temperatures will moderate
back into the teens on Tuesday, and into the low to mid 30s for
Wednesday of next week.

&&

.NEAR TERM /THROUGH SUNDAY NIGHT/...
As of 553 PM EST Saturday...Everything remains on track for the
winter storm barreling down on the North Country. After some
bonus snowfall this afternoon, lighter snow or even a few breaks
in the snowfall will be seen before conditions begin to
deteriorate heading toward midnight. However, did have to adjust
temperatures and wind chills as we have remained well below
guidance today. This will keep wind chills in the -15 to -25
degree range overnight but have opted not to issue a wind chill
advisory given the significant storm system on the way.

Previous Discussion...Have upgraded the St. Lawrence
Valley to a Winter Storm Warning, and Winter Storm Warnings
remain on track elsewhere.

Rather amazing snow event underway across the North Country,
even as low-level arctic continues to filter southward out of
sern Ontario and srn Quebec. Temperatures at BTV have been
slowly falling all day, from about 1F at 13Z to -4F at 2030Z, on
northerly winds around 10 mph. True arctic air mass with
dewpoints -10F to -20F across northern sections of the CWA. Also
seeing wind chill values of 10 to 20 below, making for
dangerous outdoor conditions with frostbite risk.

Even as this has occurred, we`ve seen 850-700mb frontogenesis
forcing in the frontal zone result in developing light to
moderate snowfall well in advance of the sfc low across the
lower Ohio Valley during the early afternoon hours. Snow
crystals are very fine - mainly needles - likely a combination
of being colder than favorable dendrite growth zone and
sublimation processes ongoing in the sub-cloud layer. We`ll be
"fighting" the replenishment of shallow arctic air throughout
this major snowfall, as north winds increase, especially Sunday
and with observed dewpoints in the -20F to -30F range around
Montreal and points north! As a result of the crystal type
(small columns and needles), visibilities will likely be very
low throughout the event, with 1/4SM to 1/2SM vsby common during
the next 24hrs due to snow and blowing snow across the forecast
area.

The 12Z NWP guidance suite indicated a northward shift in the
sfc low track and best 850-700mb frontogenesis forcing. This is
unusual given the ongoing low-level CAA (short wavelength
between systems), and thinking is that the above freezing layer
in the 850-750mb layer and potential p-type mixing is too
extreme in the 12Z NAM. The rest of the guidance is less NAM-y,
but could see a S/IP mix from 13-18Z Sunday across
Rutland/Windsor counties, and changed the forecast in s-central
VT with this package accordingly. Otherwise, looking at an all
snow event central VT and points north and west.

Overall QPF has also increased, especially across northern VT
and northern NY. As a result snowfall has been increased for
northern zones, and decreased slightly for Rutland/Windsor
counties as S/IP mix reduces frozen ratio. Have upgraded the St.
Lawrence Valley to a Winter Storm Warning with this package,
with 8-12" generally expected there. The remainder of the CWA is
in the 12-18" range, and good potential for 1-2" snowfall rates
9-15Z Sunday morning with best frontogenesis forcing as low-
level wind fields increase around deepening low pressure passing
to our south. Have lowered snow ratios down as low as 12:1, but
not expecting the snow to be clinging to trees and powerlines
given ambient surface temperatures. Thus, power outage threat is
low with this event.

For impacts, mainly looking at significant to dangerous travel
conditions CWA-wide late tonight through Sunday morning. This
will be because of 1-2"/hr snowfall rates and wind chills of 10
to 20 below, especially across northern sections. Blowing and
drifting will also increase on Sunday morning. Travel is
generally not advised due to the dangerous cold and poor road
conditions/low visibility overnight into Sunday morning.

Snowfall will gradually taper off Sunday afternoon into Sunday
night, but will see continued orographic snow, and even some
lake effect off Lake Champlain continuing. North winds 15-25
mph, with gusts to 35 mph, will maintain blowing and drifting
snow through Sunday night as low pressure moves into the
Canadian Maritimes. Frigid temperatures across the region Sunday
night, generally 5 to 15 below zero, with wind chills 20-35
below.

&&

.SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
As of 319 PM EST Saturday...Dangerously cold wind chill expected
Monday morning with values between 20 to 40 below zero. Areas
of blowing and drifting snow continue into Monday with chances
for snow showers across the northern mountains, and near Lake
Champlain.

It continues to appear that the 925mb temperatures drop to
between -25c and -30c Monday morning, and p-gradient remains
moderately strong on western periphery of departing low
pressure. It will be dangerous cold with highs only -5F to +5F,
and wind chills far below zero. May see an additional 1-2" snow
accumulation across the Champlain Valley and into
n-central/nern VT with continued orographic snow shower
activity.

As 1038mb sfc anticyclone builds in Monday night, will finally
see snow showers end with gradually clearing skies. If winds
decouple with deep fresh snow pack and clear skies, expect
temps to quickly fall during the pre-dawn hours Tuesday.
Currently have forecast -10F to -25F, coldest in the northern
Adirondacks and across nern VT.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 253 PM EST Saturday...Active weather anticipated for the long
term, though we will be trending warmer. Tuesday will be the
quietest day with high pressure cresting over the region in the
morning, then shifting east through the afternoon and evening hours.
As such, we`ll finally see a reprieve from the bitter cold as flow
turns to the southwest. Our next system arrives Tuesday night into
Wednesday, as low pressure slides up along or just north of the St
Lawrence Valley and drags its attendant cold front through the North
Country. Warm air advection snow starts Tuesday night and continues
through Wednesday, with some rain possibly mixing in across the
wider valleys as temperatures warm into the lower/mid 30s.
Uncertainty grows Wednesday night onward as another low is progged
to slide along the front which will be positioned somewhere in the
New England vicinity. Timing and position differ significantly on
this frontal passage and the second low, which has implications for
precipitation type and amounts. The system does look to sweep out by
the end of the week, with an upper trough to move in thereafter.
Overall, this means at least a chance for precipitation through just
about the entire period. After warmer temperatures Wednesday and
Thursday, we will once again drop to colder than normal for the end
of the week.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Through 18Z Sunday...VFR conditions this afternoon will give
way to widespread MVFR-IFR conditions as slight snow moves into
the region from the southwest after 22Z. Conditions will to
worsen after 06Z as heavier bands of snow move in bringing
widespread LIFR conditions throughout the overnight hours. By
morning, snow begins to lighten but northerly winds increase to
10-20 knots and with that blowing snow conditions are expect at
most terminals with after 15Z, with RUT seeing it much earlier
as they will see an easterly wind after 06Z.

Outlook...

Sunday Night: Mainly VFR, with areas MVFR possible. Chance SHSN,
Areas BS.
Martin Luther King Jr Day: Mainly VFR, with local MVFR possible.
Chance SHSN.
Monday Night: VFR. NO SIG WX.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. Chance SHSN.
Wednesday: Mainly MVFR and IFR, with areas VFR possible. Likely
SHSN, Likely SHRA.
Wednesday Night: Mainly MVFR, with local IFR possible. Chance
SHSN.
Thursday: MVFR/IFR conditions possible. Chance SHSN.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Storm Warning until 4 PM EST Sunday for VTZ001>012-
     016>019.
NY...Winter Storm Warning until 4 PM EST Sunday for NYZ026>031-034-
     035-087.

&&

$$
SYNOPSIS...Banacos
NEAR TERM...Banacos/Clay
SHORT TERM...Banacos
LONG TERM...Hastings
AVIATION...Verasamy



 
 
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