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  Wednesday November 14, 2018

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 130905
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
405 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 /THROUGH WEDNESDAY/...
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 /WEDNESDAY NIGHT THROUGH THURSDAY/...
As of 400 AM EST Tuesday...High pressure will be cresting
overhead Wednesday night into Thursday and this will lead to
some rather cold temperatures Wednesday night. 925mb temps will
be in the -11C to -14C range and that supports lows in the
single digits to low teens. The challenge will be that if we do
get that cold, then with a lake water temperature in upper 40s
we should see a significant lake response. So I`ve added some
cloud cover directly over Lake Champlain and just to the east as
light winds should push some of those clouds into the eastern
Champlain Valley. Once the high crests over the North Country
on Thursday the flow will be light enough that I believe we`ll
see some tea kettling effect where there are clear skies across
most of the North Country with mostly cloudy to overcast skies
right next to Lake Champlain.

Temps should warm into the upper 20s to low 30s in the valleys
under clear skies and no chance for precip on Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
As of 400 AM EST Tuesday...Heading into the weekend we`ll see
another round of moderate snow moving into the region. An upper
level cutoff low pressure system will end up phasing with a
developing coastal low on Friday morning. Consensus guidance
continues to be in fairly decent agreement with the low track
moving just off Cape Cod but west of the benchmark. The 700mb
closed low tracks south of the region which should push quite a
bit of moisture into the atmosphere before the precip starts to
fall. Expect the snow to start falling early Friday morning and
we should get a quick burst of some moderate snowfall Friday
morning as the surface low deepens to our east. I`d anticipate
the eastern slopes seeing the highest totals initially as the
easterly flow should enhance the surface lift.

The temperature profile continues to be on the marginal side in
the valleys but the 00z suite trended colder with more snow. We
could be looking at another significant system bringing a round
of heavy wet snow. Its too early to have specific snow totals
but if trends continue, the entire region should see plowable
snow. Additionally snow ratios are on the lower side of climo
meaning we`ll need to monitor for potential impacts from heavy
wet snow.

After the low pressure system pushes out of the region the
upper level pattern shifts to fast nearly zonal flow with
modest high pressure at the surface. Temps will start out the
weekend on the mildish side with highs in the upper 30s to low
40s but will quickly drop down below normal for Sunday into
Monday.

&&

.AVIATION /09Z 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...Deal
LONG TERM...Deal
AVIATION...Taber


 
 
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