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  Wednesday November 14, 2018

 

NWS Area Forecast Discussion


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415
FXUS61 KBTV 122323
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
623 PM EST Mon Nov 12 2018

.SYNOPSIS...
A mix of rain and snow will enter the North Country after
midnight tonight and spread toward during the early morning
hours. Most locations will see accumulating snowfall by sunrise
with 1 to 3 inches in the deeper valleys, 3 to 6 inches across
the Adirondacks and central Vermont and 4 to 8 inches across
northeastern Vermont. Snow may mix with rain in the deeper
valleys and central Vermont during the afternoon hours but will
change back to snow as precipitation tapers off Tuesday evening.
Gusty winds will then develop behind the low Tuesday night with
winds of 25 to 40 mph expected to continue into Wednesday.
Thursday will be the one nice day, albeit nearly 15 to 20
degrees below normal in regards to temperatures. Another storm
system approached Thursday night into Friday with rain, snow and
mixed precipitation possible.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
As of 623 PM EST Monday...Quiet conditions prevail for the next
few hours before some winter weather impacts the region. Made
some minor tweaks to temperatures and sky grids based on surface
obs. Stream of mid and high level clouds are moving over the
region in association with the warm conveyor belt. A baroclinic
leaf is noted in satellite imagery - a classic signature for
surface cyclogenesis, which should be under way shortly along
the Mid-Atlantic. All remains on track for the upcoming winter
weather and the previous discussion is below. Have a good night.

PREVIOUS DISCUSSION...
Cloud cover will quickly move into the region come this evening
which will help to moderate overnight temperatures with
readings in the low to mid 30s (which is quite the contrast from
the single digits to lower 20s seen this morning). Come
midnight tonight, southern Vermont will begin to see a mix of
rain and snow as a rapidly developing low pressure system
quickly pushes north along the east coast. As the low continues
to stream northward, precipitation will spread from south to
north.

Initially, it looks like the Champlain and St. Lawrence Valleys
will see a mix of rain and snow as surface temperatures are
expected to reside in the mid 30s. However, the nice dry layer
brought on by the aforementioned transient high will provide the
opportunity to cool the lowest levels of the atmosphere. As
precipitation aloft falls through this dry layer, the layer will
begin to cool and saturate. As this happens, rain at the
surface will quickly change to all snow with the now colder
temperatures both at the surface and aloft. This should allow
for the deeper valleys to see snow accumulations of 1 to 3
inches. It is worth noting that the forecast is very sensitive
to change as the boundary layer temperatures are not well
handled by the models. A change of a degree or two either warmer
or colder could easily bring less or more snowfall to the
deeper valleys. Southerly winds will help usher in warmer air
into the deeper valleys during the later morning and early
afternoon hours which supports a transition from snow to all
rain. The period of rainfall will be rather short-lived with
temperatures aloft cooling behind the low pressure system as it
exits to our northeast.

For the northern Adirondacks and central Vermont, it looks like
the majority of the event will remain snow. That being said, a
strong push of warm air will skirt southern Vermont during the
afternoon hours which could cause some of the lower elevations
to briefly mix with or change to rain. Anything at the 1500 ft
elevation or higher will likely remain snow as the warm air is
rather shallow. The highest amount of snow is likely to fall
over northeastern Vermont as all the dynamics should line up
over them perfectly. With the current track of the lower over
Long Island and into Rhode Island and eventually the Atlantic,
the warm air will likely never make it into northeastern
Vermont. In addition, a strong band of frontogenesis will couple
with deep moisture tracking northward with the low to produce
moderate to heavy snowfall after midnight tonight. This could
lead to 4 to 8 inches of snow with up to a foot possible at the
highest peaks.

To sum up everything above, the snowfall amounts will be very
elevational dependent. Due to the challenges in forecasting
boundary layer temperatures while the column adiabatically
cools, some locations may not see accumulation snowfall. The
higher the elevation, the higher the likelihood of accumulating
snowfall with the magic number being around 1500 ft tonight and
tomorrow. To finish things off, Tuesday night will be very
windy on the backside of the low pressure system. Strong
pressure rises will help to compact the pressure gradient and
bring gusty winds in the 25 to 40 mph range. This event doesn`t
look as strong as the event a week ago, but it could compound
the issue of heavy wet snow and lead to additional power
outages.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY/...
As of 327 PM EST Monday...As deep surface low (975mb) pulls
away through the Gulf of St. Lawrence Wednesday morning, will
see a strong low-level CAA regime across nrn NY and VT, with
continued moderate gradient flow. Combination of steep low-level
lapse rates and good mixing will result in gusty NW winds of
15-25 mph, with gusts 30-35 mph possible during the morning
hours. Should see p-gradient gradually subside during the
afternoon hours. With 850mb temps of -17C to -19C, Wednesday
will also feature unseasonably cold temperatures, with highs
only in the 20s (generally 15-20deg below climo mean). Will see
wind chill values in the single digits to teens, and below zero
across the higher summits. Air mass is quite dry, but may see a
few flurries at times, especially across nern VT.

Surface high pressure builds ewd from the Great Lakes region,
resulting in diminishing winds and potential for excellent
radiational cooling on Wednesday night. Overnight lows generally +5F
to +15F, warmest in the Champlain Valley. Skies will be mainly
clear, but may see a ribbon of stratocu across the long-axis of Lake
Champlain with lake-induced instability and upward flux of moisture
from the relatively warm lake waters.

High pressure remains in control on Thursday, with mostly sunny
skies, and potential for developing light southerly winds as center
of sfc anticyclone shifts into the Gulf of Maine by afternoon.
Temperatures will moderate somewhat, with highs in the upper 20s to
mid 30s. The coldest highs are likely across Vermont`s Northeast
Kingdom. PoPs NIL.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 327 PM EST Monday...Another deep, east coast mid-latitude
cyclone is expected to develop along the Carolina coast
Thursday night, before tracking newd to near Cape Cod/sern
Massachusetts by 18Z Friday. Good agreement in the 12Z
ECMWF/GFS/FV3 on general track and timing of synoptic features.
This system has a better chance to develop a closed 850/700mb
low to our south (as compared to Tuesday`s system). Thus,
anticipating a slower forward movement and more prolonged E/SE
fetch of rich moisture from the Gulf of Maine and the open
Atlantic. Vertical temperature profiles may become marginal for
snowfall, especially at lower elevations across VT with
potential for marginal PBL temps as well. Forecast reflects
relatively high PoPs (60-80%) later Thursday night thru Friday,
with a rain/snow mix at lower elevations, and mainly snow at
higher elevations, based on current indications. Precipitation
may be moderate to heavy at times, and for higher elevations and
across much of nrn NY, will definitely need to monitor for
potential significant impact from heavy wet snow. We`ll continue
to monitor.

Once this vertical stacked low departs, a strong zonal flow pattern
sets up across the nrn CONUS. Appears an embedded shortwave trough
and associated sfc front will shift ewd from the Great Lakes
sometime Saturday night, and may result in a round of snow showers
or possible snow squalls. This will be followed by colder and drier
conditions for Sunday and Monday. Highs on Saturday expected in the
upper 30s, but only in the mid-upr 20s for Sunday and Monday.

&&

.AVIATION /23Z MONDAY THROUGH SATURDAY/...
Through 18Z Tuesday...VFR conditions with SCT-BKN040-080 will
prevail thru 05Z. No vsby restrictions foreseen this aftn/eve.
Thereafter, will begin to see a mix of rain and snow overspread
the region from south to north during the pre-dawn hours
Tuesday. Anticipate periods of 1SM -SN 08-15Z, with potential
for periods of a rain/snow mix from the Champlain Valley ewd.
During mixed rain and snow, vsby will likely improve to 3-5SM.
Ceilings will generally lower to MVFR by 07-08Z, with periods of
IFR ceilings and TRRN OBSCD between 09-15Z. Should see
precipitation begin to wind down from SW-NE during the 15-18Z
time frame on Tuesday.

Outlook...

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

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory from 1 AM to 6 PM EST Tuesday for
     VTZ008-010-016>019.
     Winter Storm Warning from 1 AM to 6 PM EST Tuesday for VTZ003-
     004-006-007.
NY...Winter Weather Advisory from 1 AM to 6 PM EST Tuesday for
     NYZ029>031-034.

&&

$$
SYNOPSIS...Clay
NEAR TERM...Haynes
SHORT TERM...Banacos
LONG TERM...Banacos/Taber
AVIATION...Banacos



 
 
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