FXUS61 KBTV 241726
Area Forecast Discussion
National Weather Service Burlington VT
1226 PM 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.
.NEAR TERM /THROUGH SATURDAY/...
As of 913 AM EST Friday...Few small changes were made with the
update this morning. Lowered temps for next couple hours,
especially across eastern VT, as the rate of rise is a little
slower than originally forecast. Also increased cloud cover
across the area as high clouds are currently moving eastward
and expected to stick around through the afternoon. Will keep an
eye on high temps for the day with the additional cloud cover,
but no changes were made to max temp at this point. If mixing
occurs, could easily see high temps near 40. Rest of the going
forecast remains in good shape.
Previous Discussion...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. 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 expect 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
.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY/...
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
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 hollows 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
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
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
.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
Through 18Z Saturday...VFR conditions will continue through the
first part of the TAF period with light and variable winds
tonight, trending southerly beyond 06Z Saturday. Lower ceilings
will be possible after 00z as recycled maritime air advects
into the region, with the greatest chance of a BKN deck around
2000ft agl at KMPV. Patchy -DZ or -FZDZ possible mainly at KMPV,
but could impact KMSS as well. This could bring reduced
visibilities down to 4SM-6SM. Patchy drizzle lifts around 12Z as
next system approaches. Wind speeds increase to 5 to 10 knots
with higher sustained winds and gusts at KRUT. Some LLWS will be
possible at KSLK after 15Z and currently forecast WS020/16035KT.
Precipitation should hold off to 18Z Saturday.
Saturday Night: Mainly MVFR, with local IFR possible. Definite
RA, Definite FZRA.
Sunday: Mainly MVFR, with local IFR possible. Chance SHRA, Chance
Sunday Night: Mainly MVFR, with local IFR possible. Chance SHSN.
Monday: Mainly MVFR, with local IFR possible. Chance SHSN.
Monday Night: Mainly MVFR, with local IFR possible. NO SIG WX.
Tuesday: Mainly MVFR, with local IFR possible. NO SIG WX.
Tuesday Night: Mainly MVFR, with local VFR possible. NO SIG WX.
Wednesday: Mainly VFR, with areas MVFR possible. NO SIG WX.