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  Monday January 21, 2019

 

NWS Area Forecast Discussion


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FXUS61 KBTV 190911
AFDBTV

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
411 AM EST Sat Jan 19 2019

.SYNOPSIS...
A major winter storm is on tap for the North Country tonight through
Sunday as low pressure over the southern Plains this morning tracks
through the the Tennessee Valley today and up the East Coast Sunday.
Steady snow will develop across the region late this afternoon and
evening, and become heavy at times tonight into Sunday morning.
Snowfall rates of 1 to 2 inches per hour are possible, 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 expected in the wake of
the storm for the Sunday night through Monday night period.
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/...
As of 406 AM EST Saturday...Really only noise level changes made to
the previous forecast with very good model consistency persisting
and no changes made to current winter weather headlines. Early
morning water vapor shows our impending winter storm across the
southern plains with several lines of convection and lightning noted
across TX/AR/LA/MS. Overall track of the system today through Sunday
remains the same moving east-northeast into the Tennessee Valley
this afternoon, to around D.C. by 12Z Sunday, and eventually into
the Gulf of Maine by 00Z Monday. Ahead of system, quiet and cold
conditions will be in place across the North Country this morning
with temps in the single digits and teens as high pressure over
James Bay filters southward into the region. Some concern remains
across northern areas where drier/arctic air will be in place when
snow arrives later this afternoon and evening, and this is shown
well in the NAM low level RH fields which don`t fully saturate until
later tonight into Sunday morning. As such, we continue to highlight
a sharp gradient in the snow totals, especially across the St.
Lawrence Valley into the northwest Adirondacks. On the flip side,
across central/southern Vermont, we continue to see the potential
for strong frontogenetic forcing in the 850-700mb layer late tonight
through Sunday morning, where within a mesoscale band we could see
1-2"/hr snowfall rates from around 06-15Z Sunday. All that said,
only minor changes were made to the storm total snowfall amounts
with a general 6-12" across northern New York, least in the St.
Lawrence Valley, and 10-18" across Vermont with the lowest totals
near the Canadian border.

Additional threats during the storm will be cold temperatures and
winds. Temps won`t budge out of the single digits north to low teens
south through the period with just some slight cooling across the
St. Lawrence Valley tonight into the single digits below zero. Add
in some increasing northerly winds Sunday in the 15 to 25 mph range
and gusts to 35 mph in the Champlain Valley, and we`ll be looking at
areas of blowing snow and wind chill values of -5F to -20F.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 415 PM EST Friday...Dangerously cold wind chill expected Sunday
Night into Monday morning with values between -20 and -40 below
zero. Areas of blowing and drifting snow continue into Monday.

The combination of departing 988mb low pres over eastern Maine and
building 1038mb high pres will create brisk northwest winds and
bitterly cold wind chills Sunday Night into Monday, as 925mb temps
drop btwn -25c and -30c. Expect wind chill values btwn -20 and -40
below across the entire North Country, with the core of the coldest
values btwn Midnight and 10 AM Monday. Wind chill highlights will be
needed for this time period. Lows range from -5f to -20f overnight
with highs on Monday +5f to -10f depending upon location.

Synoptic setup shows deepening and closing off 5h circulation across
western/central NY, while sfc low pres moves into the Canadian
Maritimes. This creates north/northwest 925mb to 850mb upslope flow
of 35 to 45 knots, as deeper 925mb to 700mb rh rotates back across
our northern and central CWA Sunday Night into Monday. My experience
tells me we low level caa, upslope flow, and lingering moisture with
closing off system its going to take awhile to shut down the snow
machine, especially eastern CPV and northern/central Green
Mountains. The meso-scale setup is very interesting, as moderate to
extreme instability will be present off Lake Champlain as very cold
air moves over relatively warmer waters, while north/northwest flow
will enhance low level convergence on eastern side. BTV4km shows
strong, but shallow lift thru 15z Monday from cpv convergence on
brisk northerly winds.  Froude numbers show strongly blocked flow
with values >0.50, supporting additional snowfall. The big question,
given the extremely cold thermal profiles and snow growth layer near
the sfc, what are the snow ratio`s? My initial thoughts it will be
needles with very small flake size, but reduce visibilities in the 1
to 2sm range across the western slopes/northern dacks and eastern
cpv thru 18z Monday. Have noted 00z BTV 4km shows additional qpf of
up to 0.10 at BTV from 00z Monday thru 18z with model progged snow
ratio`s of 25 to 30 to 1, which would support an additional 2 to 4
inches locally. For now, I have increased pops into the likely/cat
range with additional snowfall of 1 to 3 inches. Meanwhile, away
from the upslope snow showers and cpv convergence, lingering
flurries and light snow shower activity will persist, but
accumulations will be limited.

Monday night 1039mb high pres builds toward northern NY and winds
should gradually diminish toward 12z Tues. If winds decouple with
fresh snow pack and clear skies, expect temps to quickly fall toward
sunrise. Crntly have -10f to -25f, but some colder sites in the
southern SLV/dacks could be near -30f, if winds decouple.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 240 PM EST Friday...ctive period of weather continues with next
system arriving on Weds, with the potential for an additional
wave developing along sharp boundary on Thursday into Friday.
This period is highlighted by plenty of uncertainty with regards
to large scale synoptic pattern and associated low level
thermal profiles. Models in decent agreement with a period of
waa snow on Weds, with strong 850mb jet of 50 to 60 knots,
producing some localized shadowing in the cpv. Expect a general
1 to 3 inches for this event with localized higher amounts in
the high peaks and northern Greens. Initially thermal profiles
are cold enough for all snow, but warm just enough toward the
end for maybe a light mix, especially western dacks and southern
CPV.

Overall pattern for late week shows deepening mid/upper level trof
across the central conus, while potent short wave energy rounds base
and enhances sfc low pres across the se conus. This general idea
looks reasonable, but uncertainty remains with the system tracking
either to our west or along the coast. GFS/FV3 and CMC show a more
eastern track and cooler, while UKMET is the western outlier and the
ecmwf is the eastern outlier. For now have utilized superblend
guidance and will mention high chance/low likely with thermal
profiles supporting mostly snow. Will continue to fine tune the
forecast over the next couple of days. Otherwise, temps warm into
the mid 20s to mid 30s on Weds, before cooling back below normal by
the end of the week.

&&

.AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
Through 06Z Sunday...General trend through the overnight will be
for current BKN-OVC MVFR/VFR to lift to a SCT-BKN mid level deck
after 09Z. VFR then continues in the mid/late afternoon where
thereafter conditions will deteriorate again to MVFR/IFR as
light snow moves into the region from southwest to northeast.
Winds NNW 5-15kts overnight trend NNE at 5-10kts this afternoon

Outlook...

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

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Storm Warning from 4 PM this afternoon to 4 PM EST
     Sunday for VTZ001>012-016>019.
NY...Winter Storm Warning from 4 PM this afternoon to 4 PM EST
     Sunday for NYZ028>031-034-035.
     Winter Weather Advisory from 4 PM this afternoon to 4 PM EST
     Sunday for NYZ026-027-087.

&&

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


 
 
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