Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1240 am EST Sat Dec 27 2014
weak high pressure located over the Middle Atlantic States will
continue to provide our region with a west wind and much above
normal temperatures through the weekend. A stronger cold front
will sweep across the region on Saturday night into Sunday morning
with another chance for rain showers...along with cooler temperatures
by early next week.
Near term /until 6 am this morning/...
as of 1232 am EST Saturday...minor tweaks to going forecast,
adjusting temperatures in the CT River Valley and portions of
south central Vermont to account for less cloud cover and light to
calm winds, leading to slightly cooler temperatures expected in
those areas this morning. Otherwise, winds out of the S-SW
generally 5 kts or less and variable cloudiness...but bulk of overcast
skies across northern two-thirds of the area forecast well.
Short term /6 am this morning through Sunday night/...
as of 340 PM EST Friday...mid/upper level ridge continues to build
across our forecast area...as 1000 to 500mb 540 line lifts north of the
international border by 18z Saturday. This low level warm air advection on south
to southwest winds of 5 to 15 knots will result in another day of
much above normal temperatures. Prognosticated 850 mb temperatures near 0c...with good
mixing would support temperatures near 50f with full sunshine...but with
clouds and limited mixing levels will trend above guidance and
mention highs 30s mountains to m40s valleys. A few upper 40s possible
if more sun develops than expected...but soundings show plenty of
moisture between surface and 850mb...similar to Friday. Also...a few
light sprinkles or flurries will be possible mainly in the mountains
after 18z Saturday...given relative humidity profiles and upslope southwest flow.
On Saturday night...surface gradient increases with approaching cold
front..along with prognosticated 850 mb jet of 45 to 55 knots. This will cause
shadowing of precipitation fields in the cpv and parts of the lower CT
River Valley on Sat night...as breezy southwest winds develop. In
addition...as deeper ribbon of 850 to 500mb relative humidity approaches our
County Warning Area...the best 500 mb support is lifting northwest of our forecast area...and relative humidity
fields weaken...along with the associated quantitative precipitation forecast. Given the lack of
cold air at the surface and aloft...not anticipating any freezing rain
or snow associated with this weak system...only a brief 1 to 3
hour window of rain showers with quantitative precipitation forecast confined mainly to the mountains
the highest quantitative precipitation forecast values of 0.05 to 0.10 will be northern dacks into
the northern greens...with only a trace to a few hundredths in the
valleys. Latest guidances shows low level cold air advection lagging several hours
behind initial ribbon of moisture...so as thermal profiles cool
enough to support snow in the mountains...best moisture is east of our
County Warning Area. A few leftover flurries or light snow showers will be
possible on Sunday associated with upslope follow...but moisture is
limited in favorable snow growth region. Will trend toward the
warmest guidance on Saturday night...with clouds and southerly
winds...especially slv/cpv...with coolest readings in the valleys
of eastern Vermont. Lows will range from the m30s to m40s.
Sunday-Sunday night...strong low level cold air advection develops with temperatures
falling throughout Sunday...especially across the higher terrain with
prognosticated 850 mb temperatures dropping to -10c by 00z Monday. The lack of a
sharp boundary/thermal gradient and limited quantitative precipitation forecast will prevent icy
roads from developing. Also...soundings show good unidirectional
and mixing of winds which will help to dry llvls out. Will
mention early morning highs in the 30s mountains to 40s valleys...but
temperatures falling back into the 10s summits to middle 20s midslopes and
30s in the valleys. Temperatures will continue to fall on Sunday night with
mainly dry conditions prevailing. Cannot rule out a flurry or
light snow shower in the mountains...as low level cold air advection helps squeeze out
remaining moisture in westerly upslope follow. Lows will range from
the teens to M/u 20s on Sunday night...with west winds at 5 to 10
Long term /Monday through Friday/...
as of 328 PM EST Friday...extended period not seeing much
changeable weather with westerly flow at 500 mb and ridge of high
pressure extending east from center of the high over the central
US through the period. Cold temperatures the main issue in the
extended period. Low level flow is northwest with cold air to the
north settling across the area. 850 mb temperatures go from -12c on
Monday to -16 to -18c on Tuesday and Wednesday. Maximum surface temperatures
only in the teens with lows single digits above and below zero.
By early Wednesday morning low level flow turns more westerly and
lake effect clouds and snow will move into the area. Chance probability of precipitation
extend into western Adirondacks and clouds a little further east.
Aviation /06z Saturday through Wednesday/...
through 06z Sunday...VFR/MVFR ceilings will exist through 00z.
Eventually all areas will see MVFR ceilings after 00z through the
remainder of the period. There may be some showers moving into
northern New York after 02z...but visibilities will remain in the
VFR category through the entire period. Winds will generally be 10
knots or less through the period.
Outlook 06z Sunday through Wednesday...
06z Sunday-00z Monday...scattered MVFR in rain showers along a
cold front. Rain showers mixing/changing to snow showers over
higher terrain late Sunday when colder air moves in.
00z Monday Onward...MVFR ceilings in northern New York with westerly flow
bringing lake effect clouds into the Adirondacks. VFR in Vermont.