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  Tuesday December 11, 2018

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 102317
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
617 PM EST Mon Dec 10 2018

.SYNOPSIS...
Dry weather continues tonight with mostly clear skies and below
normal temperatures across the area. A weak boundary will cross the
area Tuesday night and will usher in another shot of cold air. High
temperatures Wednesday will be 10 to 15 degrees below normal. A
gradual warming trend is expected towards the end of the week, but
the possibility of widespread precipitation is continuing to look
less likely for the weekend.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
As of 605 PM EST Monday...Clear skies prevail across the North
Country this evening with an abundance of cloud cover to our
west. Timing this cloud cover at it moves eastward is the
forecast challenge tonight as it will strongly affect
temperatures across the region. The current thinking is that the
bulk of the cloud cover won`t move in until after sunrise on
Tuesday which should allow most places to radiate out fully
tonight. Temperatures in the low single digits to slightly below
zero are expected. We will need to monitor temps across
northeast VT and northern NY as they have the potential to drop
further than the current forecast has in the -3 to -5 range.

Previous Discussion...Quiet and dry weather is expected for
tonight through tomorrow morning before precipitation chances
increase across northern New York Tuesday afternoon. Current
satellite indicates almost entirely clear skies across the area
with temperatures ranging from the lower to mid 20s for high
temperatures today. Winds have been generally light out of the
north-northwest and will continue to decrease throughout the
evening hours as high pressure settles in. Tonight, skies should
remain mostly clear with low temperatures ranging from around
zero across the Adirondacks and Northeast Kingdom to the upper
single digits/low teens for the Champlain Valley and southern
Vermont. With conditions favorable for good radiational cooling,
have trended towards the colder side of guidance. Clouds will
increase towards daybreak from west to east as our next
shortwave approaches the area.

Winds tomorrow will be generally light out of the south-southeast
as low pressure tracks southeast out of Ontario. Temperatures
will warm slightly from today with highs in the mid to upper
20s. Latest model runs show surface flow tomorrow afternoon
across St. Lawrence valley slightly more backed to the south so
have decreased precipitation slightly for lake effect bands with
just a narrow corridor of snow possible just along the St.
Lawrence river valley. Amounts due to lake effect should be less
than 0.5". Towards 00z, precipitation chances increase slightly
for northern New York and northern Vermont as a weak boundary
approaches from the north. The best chances for snow will be
across St. Lawrence and Franklin counties of New York with weak
moisture advection off Lake Ontario and upslope flow over the
Adirondacks. Overall, the boundary will bring light snow
showers to northern New York and northern Vermont with amounts
between a dusting and half inch. The flow will turn north behind
this boundary and will usher in below- normal temperatures
Tuesday night into Wednesday.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 223 PM EST Monday...Canadian high pressure cresting to our
north over Quebec Wednesday/Wednesday night will allow for a
continuation of benign but cold weather midweek. Northerly winds
Wednesday will pull down cooler air before veering through the
night and becoming light southerly by Thursday morning as the
center of the high shifts east. Temperatures Wednesday will top
out in the mid teens to mid 20s in the early afternoon, then
fall through the evening and into the night as cold air
advection strengthens. Despite the building high pressure,
continuing to keep some clouds in the forecast for Wednesday
with the idea of moisture becoming trapped below a strengthening
subsidence inversion. However, any areas that do clear out for
Wednesday night will be under ideal radiational cooling
conditions, allowing overnight temperatures to plummet. Lows
Wednesday night will be in the single digits above (and maybe
below in a few areas) zero.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 223 PM EST Monday...A compact upper-low will approach the
area on Thursday from the west, but models continue to struggle
in handling the track of this feature. Overall fairly weak
dynamics and lack of moisture mean the impacts of the system
will be limited to just a few light snow showers and some cloud
cover. General trend with subsequent model runs is to shift the
track further south of our forecast area, so looking less and
less likely that this will have much of any impact on us. Thus,
have reduced PoPs slightly but kept them above 0 in the 5 o 15%
range. Any conditional snow accumulations would be minimal.

As we finish the work week Friday, forecast turns more complex
as both northern and/or southern stream waves have the
potential to impact the forecast area. Continued nudging PoPs
down slightly for Friday and Saturday given the trend against
phasing of the northern and southern stream energy. Thinking the
most likely scenario is a deep closed low moving eastward over
the southern tier of the country that will stay to our south,
while we are impacted instead mainly by a northern stream open
wave. However, depending on the exact track of the southern
stream closed low, we could be close to the northern periphery
of some pretty significant moisture/warm air advection ahead of
the low. Whether we get in on that better moisture
advection and resulting area of higher QPF or whether it stays
just to our south remains to be seen.

Have continued to use a blend of the GFS/ECMWF/FV3 in the
forecast package, resulting in a mix of rain and snow beginning
Friday evening/Saturday night, lasting through Saturday, and
then trending slightly drier Sunday.

&&

.AVIATION /23Z MONDAY THROUGH SATURDAY/...
Through 00Z Wednesday...VFR conditions and light winds are
expected through the overnight and early morning hours on
Tuesday. High pressure over the region should help keep skies
clear through the early morning on Tuesday when a 2500 ft
stratus deck begins to move into the region. VFR conditions
will give way to MVFR conditions after 15Z on Tuesday with the
MVFR ceilings likely not making into Vermont until after 00Z
Wednesday.

Outlook...

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

&&

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

&&

$$
SYNOPSIS...LaRocca
NEAR TERM...Clay/LaRocca
SHORT TERM...RSD
LONG TERM...RSD
AVIATION...Clay


 
 
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