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  Friday February 22, 2019

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 201146
AFDBTV

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
646 AM EST Wed Feb 20 2019

.SYNOPSIS...
High pressure will provide another dry day today with increasing
mid and upper level clouds this afternoon. After a chilly start
this morning, afternoon highs will climb into the mid 20s. A
quick moving low pressure system passing to the north and west
of the St. Lawrence River will bring developing snowfall late
this evening, with periods of snow and sleet expected during the
overnight hours. Steady precipitation will end around daybreak
Thursday. Snow and sleet accumulations will range from 1 to 3
inches from the Champlain Valley westward across northern New
York, with 3 to 5 inches of snow and sleet expected across
central and eastern Vermont. A few rain or higher elevation snow
showers will continue through Thursday. Partial clearing is
expected and southwesterly winds will contribute to valley
temperatures warming into the low to mid 40s. Drier weather and
above normal temperatures will round out the end of the week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 641 AM EST Wednesday...Winter Weather Advisories have been
posted across central and eastern VT for tonight into early
Thursday morning (01Z thru 15Z Thursday). Main impact will be
locally hazardous travel overnight into early AM Thursday.

High pressure cresting over the North Country early this morning
is providing for a chilly start, with many below zero readings
from the Adirondacks eastward across Vermont. We`ve seen
pre-dawn readings as cold as -20F at Island Pond, VT. However,
already seeing some light S-SW low-level return flow setting up
in the St. Lawrence Valley per 08Z sfc obs, and this is keeping
temperatures several degrees warmer across much of St. Lawrence
County. High pressure remains in control thru the daylight
hours, but as this high pressure center shifts to our east,
south-southwest 10-meter winds of 5-10 mph will allow
temperatures to moderate into the 23-27F range for afternoon
highs. After a mostly clear start, will see a trend toward
filtered sunshine as mid- upper level clouds advance from SW-NE
from the Ohio Valley and eastern Great Lakes later this morning
and through the afternoon hours. PoPs NIL thru the daylight hours.

For tonight, little overall change in expectations for a roughly
5-7 hour duration window of snow to snow/sleet mix
event...mainly during the late evening and overnight hours.
Surface low tracks across the northern Great Lakes region
tonight, with associated warm front lifting newd across western
and central NY. Snow will develop from SW-NE between 00-03Z with
sharp increase in isentropic ascent and 850-700mb WAA. Best UVV
occurs between 03-09Z. Secondary low development occurs late
and too far east to have any significant impact on our forecast
area. Related to this, will see SW 900-800mb flow of 50-60kts
advecting in above freezing air into the Adirondacks by 06Z, and
into the Champlain Valley by 07-08Z, resulting in a mix or
transition over to sleet. For central and eastern VT, it appears
any mixing with sleet will be brief or toward the very end of
any steady precipitation...generally moving out of the region by
12Z Thursday as a mid-level dryslot works in on aforementioned
SW flow. May see a few pockets of light freezing rain across
northern NY, but that threat is limited in duration/extent
(trace to a few hundreths).

Overall QPF remains 0.20-0.35". Likewise, models remain
consistent with highest QPF across central/eastern/nern VT.
Given QPF and p-type trends, generally looking at 1-3"
snow/sleet from the Champlain Valley wwd across nrn NY,
and 3-5" of snow/sleet for central into ern VT with colder
temperature profiles expected. Highlighted central/eastern VT
for the Winter Weather Advisory, but included possible slick
spots areawide tonight into the early Thursday AM commute in the
Hazardous Weather Outlook. Even though frozen precipitation
will be ending, may see some slow travel for the morning commute
on Thursday, especially east of the Greens. Should see melting
and improving road conditions with partial sunshine later
Thursday morning into the aftn and temperatures rising into the
low-mid 40s. Gusty south to southwest winds are also expected
Thursday. In the Champlain Valley and nrn NY, will see S-SW
winds 15-25 mph with gusts to 35 mph possible with steepening
lapse rates and good low-level mixing.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 312 AM EST Wednesday...Overall looking at a fairly quiet end to
the work week with some higher elevation show showers Thursday night
on northwest upslope flow giving way to high pressure building into
the region for Friday and Friday night. Friday will feature a slow
trend towards clearing skies as the surface high approaches,
centering over the North Country Friday night. Temps will be
seasonably cool in the teens to low 20s for lows and low/mid 30s for
highs.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 312 AM EST Wednesday...Best day of the weekend will be Saturday
as the aforementioned surface high pressure centers over the
Northeast while an upper ridge crests over the region as well. Skies
start the day mostly clear with just some increasing mid/high clouds
during the afternoon in advance of our next system. Temps will be
spring-like in the mid 30s to near 40.

Forecast remains on track going into Saturday night when our next
system arrives. Continue to see good model agreement in the overall
track and thermal profile of the system with only noise level
differences in timing and intensity. Primary low pressure developing
in the lee of the Rockies Saturday will track northeast through the
Great Lakes Sunday ushering a strong warm front through the region
early Sunday and a cold front Sunday night. Latest GFS/FV3/ECMWF
have trended warmer than yesterdays 00Z runs leading to an increased
threat of mixed precipitation with cold high pressure dammed in
place at the onset of the event. Forecast soundings indicate ptype
perhaps starts as snow late Saturday evening but rapidly changes to
a mix of snow/sleet/fzra after midnight into Sunday morning before
going over to all rain by the noon hour as surface temps rise into
the 40s area-wide. Best chance for accumulating frozen precip will
be outside the Champlain and southern St. Lawrence Valleys where
temps should stay above freezing to support a mainly rain event, but
elsewhere ice accumulations of up to a tenth of an inch looks
plausible.

During the day Sunday as precip transitions to plain rain a
complicating factor in the QPF forecast will be a strengthening
low/mid level southwesterly jet of 40-60kts which will likely
produce some upslope/shadowing effects along with gusts in the 25-35
mph range going into Sunday night. While we continue to highlight
high PoPs of 75-85%, thinking QPF will be on the low side and
showers may become more scattered in nature than the forecast
indicates, especially if the strength and location of a mid-level
dry slot progged to stay south of the region shifts north. Cold
front moves in Sunday night as the primary surface low tracks into
southern Quebec and we should see good areal coverage of snow
showers develop overnight with some light accumulations likely.

Snow showers linger in the mountains Monday on moist northwest flow
with the deeper valleys generally dry before high pressure drys the
whole region out for Monday night into Tuesday.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Through 12z Thursday...Dry/VFR conditions will persist thru 02Z
Thursday with developing S-SW winds at 5-10kt. Thereafter, an
approaching warm front will bring developing steady snow from
SW-NE with vsby falling into the 1-2SM range between 02-03Z
Thursday. Will see general IFR snowfall continue through 08-09Z
before mixing with sleet and possible brief freezing rain toward
daybreak Thursday. Once the transition to mixed precipitation
occurs, should see general MVFR cigs/vsby conditions 09-12Z. For
tonight, winds will locally shift into the northeast at KMSS
with St. Lawrence Valley channeled flow regime. HIR TRRN OBSCD
02-12Z Thursday. Anticipate low-moderate impacts to aviation
ground ops early Thursday morning owing to accumulation of snow
and sleet (mainly 1-3" at the TAF sites).

Outlook...

Thursday: Mainly VFR, with areas MVFR possible. Chance RA, Chance
FZRA, Chance SN.
Thursday Night: Mainly VFR, with local MVFR possible. Slight
chance SHSN.
Friday: Mainly VFR, with local MVFR possible. Slight chance SHSN.
Friday Night: Mainly VFR, with local MVFR possible. NO SIG WX.
Saturday: VFR. NO SIG WX.
Saturday Night: VFR. Chance SN.
Sunday: Mainly MVFR, with local IFR possible. Likely RA, Likely
SN.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory from 8 PM this evening to 10 AM EST
     Thursday for VTZ003-004-006>008-010-012-019.
NY...None.

&&

$$
SYNOPSIS...Banacos
NEAR TERM...Banacos
SHORT TERM...Lahiff
LONG TERM...Lahiff
AVIATION...Banacos


 
 
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