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  Sunday January 26, 2020


NWS Area Forecast Discussion

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FXUS61 KBTV 240929

Area Forecast Discussion
National Weather Service Burlington VT
429 AM EST Fri Jan 24 2020

Above normal temperature are expected across the North Country
Friday as high pressure remains anchored across the Northeast
US. A complex system is poised to impact the region late
Saturday into Sunday with rain likely across most valleys and
mixed wintry precipitation for the Northeast Kingdom, northern
St Lawrence Valley and the higher summits. On Sunday, a
transition of rain or snow is expected becoming more snow over
the afternoon. Towards midweek, quiet and above normal
conditions resume for the remainder of next week.


As of 427 AM EST Friday...Last day of quiet weather today before our
next winter system arrives Saturday afternoon. 500mb heights amplify
ahead of occluded low moves eastward out of the upper Mississippi
River Valley. This will lead to another warm and dry day across the
North Country. Things still look on track for temperatures to warm
into the mid to upper 30s areawide, very similar to conditions on
Thursday. Increasing high clouds will allow for filtered sunshine
throughout the day with generally light winds under 10 mph. As low
pressure approaches the area, southeasterly winds will increase
beginning tonight through Saturday. Winds will This increasing
south- southeasterly fetch will bring recycled maritime air into the
Champlain Valley and eastern Vermont. Models soundings indicate depth
of moisture in this layer will be quite shallow, therefore thinking
potential for patchy freezing drizzle may be possible beginning
tonight through Saturday morning.

By Saturday morning, chances for precipitation will increase as the
parent low pressure center begins to approach the southern St
Lawrence Valley and a secondary low tracks near the Delmarva
Peninsula. This complex set up of multiple lows makes forecasting p-
type quite challenging across the North Country beginning Saturday
afternoon. Despite being within 72 hours of the storm, models are
still struggling with the details regarding thermal profiles with
NAM the most aggressive with developing warm nose on a very strong
60-70kt 850mb southeasterly low level jet coming off the Atlantic.
Whereas GFS/CMC/ECMWF are ~20 knots weaker with this feature. This
discrepancy between these models show vastly different p-type
solution across the area. At this time, have settled on a blend of
all 4 as to have more weight towards a cleaner isothermal profile
however do not want to discount NAM entirely given good Atlantic
fetch regardless of model choice.

With this mix of model thermal profiles, precipitation type gets
messy with potential for freezing rain beginning late Saturday
afternoon across northern St Lawrence Valley and Northeast Kingdom of
Vermont, with rain expected elsewhere outside the high terrain. Ice
accumulations should be less than 0.10" during this time frame.
Additionally, this complicated thermal profiles will have pretty
significant implications for weather type across the high terrain.
Have settled on a wintry mix at the moment but a few degrees either
way could mean either rain or snow, with the potential for freezing
rain or sleet mixing in. It`s certainly not a cut and dry situation
at all *ugh*. Winter weather headlines may be needed, however wanted
to wait for another suite of guidance to come in given such drastic
changes with the models compared to 48 hours ago. Perhaps the 12z
suite will provide better clarity on the freezing rain potential.

Lastly, gusty winds may be possible along the western slopes of the
Green Mountains late Saturday afternoon into the overnight hours
associated with this southeasterly low level jet. 925mb winds are
generally around 40kt, therefore expected winds along the spine of
the Greens between 30-40kt, with favored downsloping western areas
seeing winds around 15-20kt with gusts up to 30 kts at times.


As of 427 AM EST Friday...Complex forecast continues Saturday night
and Sunday with the forecast models still unable to agree on the
details with degree of warming aloft and degree of cooling at the
surface. The overall scenario is becoming more clear; the
upper/primary low will spin over the eastern Great Lakes while a
weak secondary will lift over/just south of our forecast area. The
strongest warm air advection and frontogenesis crosses the region
roughly 00z-08z Saturday night/Sunday morning, which is when the
heaviest precipitation would occur. Exactly what kind of
precipitation is the question. The main culprit looks to be the the
strength of the 850 mb jet; the NAM has 60+ kt and therefore has a
deeper warm nose aloft. It also keeps surface temperatures colder,
especially Saturday night. The CMC, ECMWF, and GFS meanwhile have a
weaker jet, less warming aloft (nearly isothermal in some cases),
and warmer surface temperatures. Either way, we`re only talking the
difference of a couple of degrees, which makes all the difference.
At this time, the most likely scenario would have surface
temperatures holding steady or rising slightly in the lower to mid
30s overnight Saturday night. The colder valley locations,
particularly the St Lawrence Valley due to northwest winds, and the
protected hallows east of the Greens would have the best chances for
near-freezing surface temperatures, meaning sleet or freezing rain.
The Champlain Valley would likely remain all rain overnight. Colder
air will begin to move in aloft on Sunday as the upper low moves
overhead and then shifts east by late in the day. Hence any warm
nose will erode, changing any mixed precipitation to just rain or
snow Sunday morning, and eventually all snow by late Sunday
afternoon, particularly in the mountains. Exact amounts of rain,
snow, sleet, or ice are hard to pinpoint at this time given the
model differences, but overall expect an inch or two of snow/sleet
across the higher terrain through Sunday, with around a tenth of an
inch of ice accretion possible in the St Lawrence Valley and the
sheltered valleys of eastern VT. The higher terrain of the southern
Greens may see a quarter of an inch of ice or better. Stay tuned for
later updates on this situation.


As of 427 AM EST Friday...Mountain snow showers will continue through
at least Monday as the upper low pulls away, keeping us under
northwest flow. Another couple of inches of snow will be possible
over the higher terrain. It quiets down heading into midweek with
high pressure building across the eastern CONUS. Another low
pressure system approaches late in the week but any precipitation
associated with this will hold off until the weekend. Temperatures
will remain near or slightly above seasonal normals, though a couple
of chilly nights will be possible midweek under the aforementioned
high pressure.


Through 06Z Saturday...VFR conditions will continue through the
TAF period with light and variable winds persisting through
Friday morning. Winds will begin to turn from the southeast
across the area after 20Z with winds in the 8 to 14 knot range
at KRUT & KMPV. Elsewhere, winds will likely remain below 5
knots throughout the forecast period.


Saturday: Mainly VFR, with local MVFR possible. Definite RA,
Chance SN, Definite FZRA.
Saturday Night: Mainly MVFR, with local IFR possible. Windy with
gusts to 30 kt. Definite RA, Definite SN, Definite PL, Definite
Sunday: Mainly MVFR, with areas IFR possible. Likely SHSN, Chance
Sunday Night: Mainly MVFR, with areas IFR possible. Chance SHSN.
Monday: Mainly MVFR, with areas IFR possible. Chance SHSN.
Monday Night: Mainly MVFR, with areas IFR possible. NO SIG WX.
Tuesday: Mainly MVFR, with local IFR possible. NO SIG WX.




SHORT TERM...Hastings
LONG TERM...Hastings

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