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  Monday November 18, 2019

 

NWS Area Forecast Discussion


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264
FXUS61 KBTV 160532
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1232 AM EST Sat Nov 16 2019

.SYNOPSIS...
Snow showers and squalls will come to an end and skies will
rapidly clear out after midnight, with very cold and dry weather
conditions expected for the weekend. As arctic high pressure
departs to the east, low pressure approaching from south of New
England will bring potential for mixed wintry precipitation,
including possible freezing rain, Monday into Monday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1226 AM EST Saturday...The forecast remains in good shape
this morning. Drier air is rapidly spilling into the region
behind the cold front, ending precip and clearing skies.
Temperatures will plummet through the early morning hours, but
there is some concern that winds will remain high enough to
limit just how far they can go. Have made some slight
adjustments for now, but will need to watch trends closely
through daybreak.

Previous Discussion...Surface cold front and associated line of
snow showers and embedded snow squalls (reflectivity up to 40
dbz) continues esewd across the southern Champlain Valley into
the Montpelier area at 2345Z. Brief vsby down to 1/2SM to 3/4SM
in snow along with gusty winds to 30 mph can be expected, making
for rapidly changing road and travel conditions this evening.

It continues to appear that loss of SBCAPE and weakening low-
level frontogenesis will lead to a weakening of this convective
activity through 02Z across central/s-central VT. Anticipate
just light snow showers across Rutland/Windsor counties later
this evening.

Further north, we did see a quick 0.5" to 2" snowfall with the
snow squalls in nwrn/nrn VT, along with several reports of
lightning and thundersnow from Johnson to Albany to Sheffield
(also evident in GOES-16 GLM data). Concern during the next
several hours will be the flash freeze potential, with any
standing water quickly turning to ice as temperatures plummet.
Continue to anticipate icy spots on untreated surfaces
overnight, which may contribute to accidents. Motorists should
exercise caution, as black ice is difficult to spot, especially
at night.

Previous Discussion...We continue to monitor progress of arctic
frontal boundary and narrow band of snow showers and squalls
extending from near Ottawa to NW of Montreal at 1915Z, moving
sewd around 20kt. The front will interact with better low-level
moisture streaming newd from Lake Ontario and Lake Erie later
this afternoon as the front moves into nrn NY and nrn VT. Thus,
main story through this evening will be potential intensifying
line of snow showers/squalls with brief whiteout conditions and
potential for developing icy spots on roads/highways during the
evening commute. Current trends take the line of snow squalls
into the St. Lawrence Valley between 20-21Z, and then 21-23Z for
the northern Adirondacks and Champlain Valley, into north-
central VT. Axis of PW values 0.25-0.35" across the nrn Great
Lakes into nrn NY and northern New England exists in advance of
approaching arctic boundary, which represents favorable moisture
values for an impactful snow squall event. High resolution NWP
is also showing SBCAPE values of 60-150 J/kg across the northern
half of our CWA, before lessening as front moves south of
Montpelier near/after 00Z this evening. Likewise, best sfc-925mb
frontogenesis is across the northern half of our forecast area
through 00Z, with frontal convergence weakening across
central/s-central VT later this evening, resulting in
diminishing intensity snow showers. Consistent with the above,
BTV Snow Squall Parameter shows a strong signal, and low-level
mixing behind the front supports N-NW winds gusting to 30 mph as
the front passes through. We`ll continue to message 1/4mi or
less vsby along with quick 0.5" to 1.5" snowfall accumulation
with the squalls, along with timing with the late
afternoon/evening commute. May see slightly higher snow
accumulation in upslope flow areas across the Adirondacks and
northern Green Mountains. Will be monitoring for possible Snow
Squall Warnings next 2-4 hours. Also concerned with road
temperatures above freezing currently, that there is flash
freeze potential as the front moves through and temperatures
plummet. Anticipate icy spots on untreated surfaces for the
evening commute and into tonight, coincident with arrival of
snow squall activity. Motorists should be prepared for rapidly
changing weather and road conditions and reduce speed as needed.

Temperatures in the 35-40F range this afternoon will fall
quickly in post-frontal air mass, with NW winds 15-25 mph with
gusts briefly to 30 mph. Winds should decrease below 10 mph
after midnight, along with rapid clearing. Daybreak lows will
range from 0-10F, except locally in the lower teens across
s-central VT where low-level CAA will arrive last.

With 850mb temperatures around -13C to -14C on Saturday,
anticipate very cold temperatures and ineffective sunshine with
daytime highs in the upper teens near the intl border, to the
low-mid 20s across the remainder of the CWA. With high pressure
cresting across nrn VT and srn Quebec Saturday night, excellent
radiative cooling conditions are expected. Temperatures will
drop quickly just after sunset. Looking for near- record low
temperatures Saturday night, ranging from -7F at KSLK, to the
single digits above zero across much of the forecast area. A few
of the colder hollows of far nern VT may also see below zero
readings Saturday night. PoPs NIL for Saturday and Saturday
night.

&&

.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 249 PM EST Friday...Moderating temperatures are forecast for
Sunday as high pressure slides to our east and southeasterly flow
advects in somewhat warmer air. Cloud cover from the southeast
begins to intrude later in the day. Overnight, a coastal low will
begin advancing along the Gulf Stream. For the most part, anticipate
precipitation hold off until later into Monday as opposed to
Sunday night, but a few models do begin spreading precipitation
into Vermont overnight, so have mentioned a slight chance to
chance for portions of south-central and eastern Vermont.
Overnight lows will be in the 20s with a strong inversion
overhead, meaning anything that falls would be either sleet or
freezing rain. There is quite a bit of antecedent dry air to
overcome. Amounts, if any, will be light.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 249 PM EST Friday...A second shortwave rounding a large
upper trough across the Great Lakes will come right on the
heels of a coastal low passing east of the 40N/70W benchmark.
Negatively tilted trough to the west and negatively tilted ridge
to the east allows for some southeasterly winds aloft to advect
moisture into interior New England. The 295K Isentropic
indicates ascent from easterly flow to the north of this
coastal low. Meanwhile, cool northerly winds channeling down the
St. Lawrence River Valley will keep near surface layer
conditions cooler while continued mid-level warm air advection
maintains a deep inversion layer overhead. This is fairly
unusual, and models continue to waver with regards to the
westward extent of precipitation. The latest 12Z ECMWF has
pushed precipitation east of Vermont again, and is just one
example of this uncertainty. Both deterministic and ensemble
forecast output indicates the conditional probability for
freezing rain/sleet scenario is high. Overall, relatively dry
air from the aforementioned north winds, and broad, weak forcing
for ascent indicate that precipitation should remain light in
nature. This pattern is complex though, and there will be
continued adjustments to the forecast.

By afternoon, the 0 degree isotherm will retreat back to the
International Border, and we will see a transition to rain
Monday afternoon. Portions of the St. Lawrence River Valley
will remain under cool northeast flow which could keep frozen
precipitation going longer across that area. Later in the
evening, temperatures again fall below zero, but cooling aloft
should result in a transition to sleet and then snow as the
system departs the area.

The remainder of the long term remains active, but at this time, no
feature stands out except for the next system to arrive next
Thursday night/Friday. We do moderate temperature-wise, but remain
slightly below normal.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Through 06Z Sunday...VFR conditions will prevail through the
next 24 hours. Arctic front has passed through the region,
clearing skies and ending precip. This will be the trend through
the forecast period, though there may be some lingering low
clouds along Lake Champlain due to the relatively warm waters.
North- northwest winds will be gusty to around 20 kt through
08z, then mainly 5-10 kt for the remainder of the forecast
period.


Outlook...

Sunday: VFR. NO SIG WX.
Sunday Night: Mainly VFR, with local MVFR possible. Slight chance
FZRA.
Monday: Mainly MVFR, with areas VFR possible. Chance RA, Chance
FZRA, Chance PL.
Monday Night: MVFR/IFR conditions possible. Chance SN, Chance PL,
Likely FZRA.
Tuesday: Mainly MVFR, with local IFR possible. Chance SN, Chance
RA.
Tuesday Night: Mainly VFR, with areas MVFR possible. Chance SN.
Wednesday: Mainly MVFR, with local VFR possible. Slight chance
RA, Slight chance SN.

&&

.CLIMATE...
Here are some min and low max temperature records which could be broken over
the next few days.

Min Temp Records
Date    KBTV     KMPV     K1V4     KMSS     KPBG     KSLK
11-16    6|1967   4|1967  10|2003  0|1967   11|1967 -11|1933
11-17    7|1924   5|1972  20|2017 12|1980   14|1972 -10|1933

Low Max Temp Records
Date    KBTV     KMPV     K1V4     KMSS     KPBG     KSLK
11-16   22|1933  22|1967  31|2018  20|1967  29|1967  16|1933

&&

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

&&

$$
SYNOPSIS...Banacos
NEAR TERM...Banacos/Hastings
SHORT TERM...Haynes
LONG TERM...Haynes
AVIATION...Banacos/Hastings
CLIMATE...BTV



 
 
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