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  Wednesday November 14, 2018

 

NWS Area Forecast Discussion


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FXUS61 KBTV 130601
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
101 AM EST Tue Nov 13 2018

.SYNOPSIS...
Wintry weather arrives later tonight into Tuesday with
accumulating snowfall and locally hazardous travel expected.
Precipitation ends by tomorrow night with much colder air
arriving for Wednesday into Thursday. Thereafter, additional
chances for rain and snow arrive for Friday into Saturday as low
pressure track across the Northeast.

&&

.NEAR TERM /UNTIL 2 PM THIS AFTERNOON/...
As of 1250 AM EST Tuesday...Updated forecast to add Windsor
County into winter weather advisory. Thinking higher terrain
near Ludlow/Andover and Bethel will see snowfall accumulations
of 2 to 5 inches with isolated higher amounts. Otherwise, a very
difficult and complex ptype forecast continues across our cwa,
especially the cpv, where temps are near 40f. At BTV we have wet
bulbed down to 37f with dwpt climbing to freezing, which is not
cold enough to support snow. So we are going to have to wait
until the stronger dynamics arrive to help cool the column
enough for a period of moderate snow toward the morning commute.
Still expecting a 2 to 4 hour window of light to moderate snow
across the cpv, with bl temps holding in the 33 to 35f range.
How much accumulates and potential impacts is very difficult to
determine, better accumulations will be central/eastern and
northern VT, where bl temps will run btwn 29-33f during the
event. Overall, warnings/advisories look reasonable and will
only make minor adjustments to complete package at 4 AM.

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 /2 PM THIS AFTERNOON 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 /06Z TUESDAY THROUGH SATURDAY/...
Through 06Z Wednesday...Challenging aviation forecast with
moderate impacts expected this morning at mpv/slk in wet
snowfall. Expect a band of moderate snow with brief periods of
heavy snow to impact mpv/slk btwn 10-16z this morning. Vis will
be around 1/2sm with cigs hovering around ifr conditions at
these two terminal. Meanwhile, thinking a burst of snow mixed
with rain occurs at rut/pbg/btv with vis dropping btwn 1-2sm in
light snow with cigs near ifr conditions. Mss has similar
conditions this morning, but improves to mvfr/vfr by 18z with
breezy west winds developing at 15 to 25 knots. Improving
conditions will develop at pbg/btv/rut by early aftn with vfr.
Lingering clouds and -shsn activity will produce a combination
of mvfr/ifr at slk/mpv.

Outlook...

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

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory until 6 PM EST this evening for VTZ008-
     010-012-016>019.
     Winter Storm Warning until 6 PM EST this evening for VTZ003-
     004-006-007.
NY...Winter Weather Advisory until 6 PM EST this evening for
     NYZ029>031-034.

&&

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



 
 
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