Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
140 am EST Sat Dec 7 2013
a weak wave of low pressure will move from the Middle Atlantic
States this evening to a position southeast of Cape Cod by
Saturday morning. This system will bring some snow to the north
country tonight. Snowfall accumulations of one to three inches
are possible across central and southern Vermont...with little if
any accumulation across the north. Cold and mostly dry weather is
expected over the weekend as high pressure builds east from the
Great Lakes. Another low pressure system will bring snow to the
region Sunday night into Monday morning...which will transition
to a wintry mix Monday afternoon.
Near term /until 6 am this morning/...
as of 1222 am EST Saturday...light snow showers continue across southern
Vermont...into portions of Rutland and Windsor counties. As bulk of
moisture has retreated further south and east...threat of snow
showers will continue to gradually diminish this morning. Overall
forecast in good shape.
Previous discussion...southwest to northeast oriented low- level
baroclinic zone extends from central PA to central/southern
Maine. The greatest moisture is aligned along and south of the
frontal boundary. Though overcast skies continue low levels
remain too dry for snow to fall. Given recent trends in short-
range guidance and current regional composite radar presentation
showing the heaviest precipitation to the south...I think it will be
rather difficult to get much in the way of any snowfall north of
a Saranac Lake- Montpelier/St. Johnsbury line. Similar to prior
thinking...the greatest chances for light snow will be across
central and southern Vermont and into Essex County New York overnight
with amounts between d-2" for central Vermont and Essex County New York
to 1-3" in southern Vermont. So the main change with this update
was to lower probability of precipitation north. Temperatures were also running a few degrees
too cold and i've also gone ahead and increased hourly temperatures up
slightly. Lows still close to prior forecast...ranging from the
teens across the Northeast Kingdom and the 'dacks to the
middle/upper 20s in the Champlain Valley.
Short term /6 am this morning through Sunday night/...
as of 254 PM EST Friday...outside of perhaps a few mountain snow
showers or flurries Saturday into Saturday night...it will be
mainly dry this weekend with partly cloudy skies and below normal
temperatures. 850 mb temperatures continue to fall slowly during
Saturday to -13 to -15c by evening. This will allow for valley
highs only in the upper 20s and lower 30s...about 5 degrees below
normal. Min temperatures Saturday night expected to be in the teens with
single digits in the normally colder portions of the Adirondacks
and Northeast Kingdom. High pressure builds across the north
country on Sunday. Maximum temperatures a couple of degrees colder than
Saturday with highs in the middle 20s to around 30.
High pressure departs to the east Sunday evening. Meanwhile...low
pressure over the Mississippi Valley will track north-northeast
into the Great Lakes. A secondary low pressure area will develop
along the middle Atlantic coast late Sunday night and move
northeast. Both the European model (ecmwf) and GFS models hold off on bringing
light snow into the region until after midnight Sunday night. By
Monday morning...snow expected to be falling across most of
forecast area...with accumulations of an inch or two by
daybreak...and some additional accumulation to follow. Look for a
rather messy commute Monday morning.
Long term /Monday through Friday/...
as of 238 PM EST Friday...extended range forecast from Monday
onwards is largely unchanged from previous thinking as medium
range guidance remains consistent in regards to the overall large
scale synoptic pattern.
Monday still looks to be a day as low pressure moving through the
Great Lakes region will drag warm and cold fronts into the
region. Precipitation along the warm front moving in Sunday night
into Monday morning will continue to fall as snow through middle-day
before boundary layer temperatures warm enough to transition central and
southern areas to rain. Across northern areas precipitation could stay
all snow or have a slight mix with rain...but this will largely
depend on how far north the front makes it. During the transition
from snow to rain there may be brief periods of sleet per
forecast soundings across eastern Vermont...but should be short-
lived and isolated so have left it out of the forecast for now.
By the afternoon/evening hours...attending cold front shifts in
from the west with falling surface and middle-level temperatures turning
precipitation back to snow...though will be dissipating quickly by
midnight. Overall from Sunday night through Monday could see some
advisory level snows across portions of the area so stay tuned
this weekend as details become more clear.
For the remainder of the forecast period for Tuesday through
Friday...colder temperature profiles return as a broad upper trough
settles over the northeast. We'll be under fast west/southwest
upper flow with several weak shortwaves moving through supporting
some low chance probability of precipitation here and there for snow especially downwind
of Lake Ontario...but no real big accumulations are on the
horizon...sigh. There are some indications though of possible
snow squalls along a modest Arctic front sagging into the region
Wednesday afternoon/evening...but certainly way to far out to
have any confidence in such a mesoscale phenomenon. Highs during
the period will generally be in the 20s...and lows in the lower
teens to single numbers...all well below normal for mid-December.
Aviation /07z Saturday through Wednesday/...
through 00z Sunday...surface observations and composite radar loop
showing light snow has come to end across central and southern
Vermont as of 0630z Saturday. Mainly VFR conditions across the
region at this time...with some areas of MVFR ceilings in central
and southern Vermont...and the Adirondacks. Expecting conditions to become VFR
throughout the region by 15z Saturday. A ridge of high pressure
centered over the northern plains states at 06z Saturday will
build slowly east and will extend from Pennsylvania to Wisconsin
by 06z Sunday.
Outlook 06z Sunday through Wednesday...
06z Sunday through 06z Monday...VFR under high pressure.
06z Monday through 12z Tuesday...IFR/MVFR in developing snow and
mixed precipitation...as surface low pressure moves northeast
through the Great Lakes.
12z Tuesday through Wednesday...generally VFR with some areas of
MVFR with isolated to scattered snow showers.