FXUS61 KBTV 120003
Area Forecast Discussion
National Weather Service Burlington VT
703 PM EST Tue Dec 11 2018
A weak low pressure system moving in from the west will spread
some light snow showers over the area through tonight, but
accumulations will generally be under an inch. Wednesday will be
the coldest day of the forecast period before a warming trend
starts Thursday and lasts through the weekend. The next chance
for precipitation comes Friday night through Saturday as a low
pressure system passes to our south and east.
.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
As of 646 PM EST Tuesday...Compact upper shortwaves moving
across Lake Champlain during the winter along with surface
boundary and moisture is never what the synoptic models suggest.
Yes...some snow showers are expected but history has sown that
these scenarios lead to more than we bargained for. !@z FROUDE
values <0.5 with WNW flow...shortwave and surface boundary
favorable. Deep moisture is lacking but atmosphere is gradually
moistening with approaching shortwave/front and with time should
moisten. In fact...18z FROUDE has just arrived and supported
this previous thinking with greater moisture and actually
spitting out QPF, thus feel rather confident in the changes
that have been made.
Here we go...as the shortwave and boundary move into Champlan
vly by 03-04z we should see an enhancement in activity over the
lake and across Northern Champlain Vly...this should continue
til 07-08z then subside but stay locked in the mountains thru
12z. I didn`t go gang busters with snowfall amounts but
definitely increased to be noticeable. In the immediate Northrn
Champlain Vly we could see an inch or so and the western slope
communites like underhill/cambridge could witness 2-3 inches
with 4 inches along the mountains. Time will tell.
Afternoon Discussion...An upper- level wave and attendant weak
surface low over the Great Lakes is responsible for a broad area
of cloud cover spreading eastward through the forecast area
this afternoon. Southwesterly flow ahead of the feature is
supporting some light Lake Ontario-enhanced snow showers over
the Saint Lawrence Valley and extending into the northern
Adirondacks. As the area of low pressure advances eastward this
evening/overnight, clouds will thicken and lower over the area.
At the same time, the light snow showers will spread east and
bring a dusting to a half inch of snow to portions of northern
Vermont/up to an inch in portions of northern New York
overnight. These snow accumulations will mainly be restricted to
higher elevations, while the valleys will see just see a
dusting. Very little moisture is available with the system and
any snow will be light and fluffy, so not expecting the light
snow to have any real impacts.
Deep northerly flow will become established Wednesday morning
as the low/upper trough axis shifts to our east. Influx of drier
air will allow any lingering snow showers to taper off through
Wednesday morning. The area will see increasing cold air
advection with 850 mb temps falling as low as -15C during the
evening hours. Highs will range from the teens to mid 20s.
Overnight, high pressure over Quebec will sink south and set up
ideal radiational cooling conditions over much of the forecast
area (especially Vermont) with clear skies and light winds. Low
temperatures will generally be in the single digits above and
below zero, although portions of the northern Adirondacks along
with areas in Essex County Vermont could see lows below -10F.
.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
As of 312 PM EST Tuesday...The atmosphere will be quite dry. As
a result, temperatures should rise fairly quickly, on Thursday,
under the influence of clear skies and warm air advection. A
shortwave embedded within deep layer ridging should result in an
increase in cloud cover and low-level moisture by evening, so
temperatures for Friday morning should be a modest 15 to 25
degrees warmer than Thursday morning.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 312 PM EST Tuesday...Deep layer ridging will continue to
amplify on Friday and shift eastward ahead of two shortwave
troughs. Precipitation chances will increase some Friday night
into Saturday morning, but continues to trend away from being
widespread for our area. Forecast models have been fairly
consistent regarding the southern stream shortwave tracking
across the southeast, but still have modest variation in speed
for the northern stream shortwave in the Great Lakes. The trend
continues to minimize the phasing of these systems, though
pieces of vorticity peels off from the southern stream
shortwave. A new surface low will begin to develop along the
Mid-Atlantic coast as surface low pressure occludes in the
southeast. Exactly where this coastal low and where the northern
stream shortwave is located will determine where good
frontogenetic forcing and moisture convergence sets up. At this
time, this appears to take place mainly to our south and east.
As for P-type, thermodynamic profiles suggest a mix at night
across higher elevations that transitions to rain or simply all
rain followed by a transition towards sleet and snow for any
lingering showers Sunday morning. Assuming there is no phasing
of the systems, the southern stream shortwave will pass along
the Mid-Atlantic late Saturday into Sunday with high pressure
overhead, which should keep moisture south of us. Though the
latest GFS wants to place the center of the high further north
and allow moisture to make it northward and then wrap around as
the surface cyclone develops. The flow remains fairly
progressive with another shortwave shifting east next Monday
with all but the ECMWF forecasting a trough to pass across New
England. Probabilistic output has me leaning towards the ECMWF,
but forecast for the weekend remains changeable.
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Through 00Z Thursday...At 00z... light snow/snow showers moving
across northern NY and will move into northern VT by 02-03z.
MVFR-IFR for ceilings and visibility at times at NY TAF sites
will impact KPBG/KBTV as well and to lesser extent KMPV and
KRUT.Snow will abate by 05-06z in NY and 08-10z in northern VT
but low clouds and MVFR cigs continue til aft 12z with gradual
drier air and clearing aft 18z. Winds thru period will be less
than 10 knots.
Wednesday Night: VFR. NO SIG WX.
Thursday: VFR. NO SIG WX.
Thursday Night: VFR. NO SIG WX.
Friday: Mainly VFR, with local MVFR possible. NO SIG WX.
Friday Night: Mainly MVFR, with local IFR possible. Chance RA,
Saturday: Mainly MVFR, with areas VFR possible. Chance RA, Chance
Saturday Night: Mainly VFR, with local MVFR possible. Slight
chance RA, Slight chance SN, Slight chance SHSN.
Sunday: VFR. Slight chance SHRA, Slight chance SHSN.