Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
929 PM EST Tuesday Dec 1 2015
occasional rain will continue through Wednesday as a large low
pressure system affects the eastern United States. A few lingering
areas of freezing rain are still possible through about midnight
over the eastern half of Vermont. As low pressure moves up the
East Coast and colder air moves into the region...rain will change
over to snow Wednesday and last into Thursday...with some
accumulation possible in the higher elevations. Drier weather is
then expected for Friday and into the weekend.
Near term /until 10 am Wednesday morning/...
as of 929 PM EST Tuesday...next wave of light precipitation
exists from the Champlain Valley eastward. Most locations are
above freezing with the exception of the eastern third of Vermont
where localized readings in the lower 30s exist. So will continue
the Freezing Rain Advisory a little longer...but may be able to
get rid of it before midnight as this area of precipitation exits
Vermont. There should be a lull in the precipitation for about 3-4
hours...but already seeing areal coverage of precipitation
expanding back across western New York and western Pennsylvania.
This activity will then move back into northern New York and
Vermont toward daybreak.
a wave of low pressure has formed off of the New Jersey coastline this
afternoon and will travel just inside the benchmark overnight.
This will spread another round of rain/showers into the
northeastern US...however the most widespread precipitation associated
with this should remain off to our south and east...leaving US
with on/off showers. A third wave of rain/showers will move in
from the south and west late tonight and into Wednesday morning as
the frontal zone moves east and moisture convergence increases.
Precipitable water values approach 1" by 12z Wednesday.
As this frontal push of rain/showers tapers off...frontal zone will
gradually shift south and eastward. Expecting a lull in the
precipitation late Wednesday morning into Wednesday afternoon
before another surface low developing in the Middle Atlantic States
moves northeastward up the coastline bringing yet another slug of
rain for Wednesday evening.
Temperatures will be steady this evening in the 30s...with some
gradual rise overnight. Temperatures continue to rise Wednesday with
highs in the 40s for most.
Short term /10 am Wednesday morning through Thursday night/...
as of 320 PM EST Tuesday...a wet accumulating snow event for the
mountains is likely late Wednesday night into Thursday.
Deep closed 500 mb/7h circulation currently located over the Central
Plains will track into the central Great Lakes by 00z Thursday as
progressive flow aloft continues. As potent 500 mb energy rounds
middle/upper level trough surface low pressure will develop across the
middle Atlantic coast by 03z Thursday and tracks northeast into the
Gulf of Maine by 12z Thursday...as initial surge of deep 850 to
500mb moisture shifts east of our County Warning Area. Additional moisture will wrap
back into our central and northern forecast area by early Thursday
morning as closed 500 mb/7h circulation moves directly overhead. The
cooling aloft associated with this system and low level cold air
advection developing on northwest winds will help produce cold
enough thermal profiles to change rain over to snow...first in the
mountains of New York...then in Vermont. Using the 925mb to 850mb 0c line
supports precipitation changing to snow by 03z northern dacks
above 1500 feet and by 06z northern Green Mountains from Stowe to
Jay Peak...and lowering to near the valley floor by 12z Thursday.
A brief break in precipitation is expected on Thursday morning as
we shift from the synoptic scale lift from surface low pressure
and strong right rear quadrant of 250mb jet to a mesoscale lift
associated with developing upslope flow and wrap around moisture.
Thinking by 15z Thursday developing 850 to 700mb flow of 15 to 30
knots with plenty of 1000 to 700mb relative humidity and
associated upward vertical velocity fields will help in
redevelopment of mainly snow. Best moisture will be across the
northern dacks into the mountains of central and northern
Vermont...including the eastern Champlain Valley. Will mention likely
to Cat probability of precipitation from Wednesday night through Thursday across our central
and northern County Warning Area...with highest values over the mountains have noted
that even with the system being closed off the circulation remains
progressive with deep layer moisture shifting east of our County Warning Area by
09z Friday. Will continue to mention likely probability of precipitation for Thursday
night in the mountains and taper off to chance by 12z Friday.
Snowfall will be highly elevation depend given thermal profiles
across our County Warning Area...with the highest amounts occurring above 2000 feet
from the northern dacks into the northern Green Mountains. Early
indications suggest 4 to 8 inches in these areas with 1 to 4 inches
between 1000 and 2000 feet and only a trace to an inch or so below
1000 feet across the northern portions of the Champlain and Saint
Lawrence valleys. Little accumulation is over the southern Saint
Lawrence valley or lower CT River Valley near vsf. A Winter
Weather Advisory is likely for portions of the northern dacks into
the mountains of the central/northern Green Mountains from Wednesday
night into Thursday evening. Expecting accumulating snowfall will
dissipate across the dacks by 03z Friday and around 06z as
Temperatures will cool into the middle/upper 20s by 12z Thursday in the
mountains and in the Lower/Middle 30s over the Champlain Valley and
parts of the lower CT River Valley. Little change in thermal
profiles are expected on Thursday with chilly northwest winds and
low level cold air advection developing on back side of surface low
pressure lifting across the Gulf of Maine. Lows will fall back into
the 20s to near 30 by Friday morning...with some colder values
possible in the higher mountain towns associated with fresh snow
Long term /Friday through Tuesday/...
as of 315 PM EST Tuesday...overall very little change from
previous forecast thinking as medium range guidance remains in
good agreement. In short, looking at generally mild and dry
weather for the majority of the extended period.
Forecast period begins Friday where a weak secondary upper trough
will be shifting through the area. Feature is pretty moisture
starved at the surface so despite decent upper dynamics think we'll
only see some widely scattered rain/snow showers, mainly across the
higher terrain. Friday night into Saturday a large scale upper ridge
and surface high build back into the area and dominate the north
country's weather right through the weekend with sunny/clear/dry
conditions expected. Dry conditions continue into the early part of
next week as well with surface high pressure dominating, but aloft a
weak backdoor cold front will bring an increase in clouds late
Sunday night through Monday before the upper ridge becomes
reestablished on Tuesday.
Temperatures through the period will be seasonal to slightly above normal
with highs ranging from the middle/upper 30s to middle 40s, and lows in
the middle 20s to low 30s.
Aviation /03z Wednesday through Sunday/...
through 00z Thursday...expect quite a bit of MVFR and IFR
conditions with respect to ceilings and visibilities through the
period as occasional rain moves across the area. There will even
be periods of LIFR ceilings...especially after 08z.
Outlook 00z Thursday through Sunday...
00z Thursday - 06z Friday...MVFR/IFR as low pressure system tracks
through the region. Rain transitions to snow showers Wednesday night
through Thursday before ending.
06z Friday - 18z Friday...mainly VFR under brief high pressure.
18z Friday - 12z Sat...VFR/local MVFR in scattered snow showers.
12z Sat - 00z Monday...trending to VFR under building high pressure.
Vermont...Freezing Rain Advisory until midnight EST tonight for vtz003-