Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
130 PM EDT Thursday Sep 18 2014
a cold front will drop south across the region this morning
bringing a period of cloudy conditions...along with the chance of a
few light showers or sprinkles. Winds turn northerly behind the
front resulting in below normal temperatures. Strong high pressure
builds in tonight and Friday...setting up a widespread frost
tonight with temperatures near to below freezing in most sections
away from Lake Champlain. Fair and seasonably cool conditions
continue on Friday...followed by breezy and warmer weather for
Near term /until 7 PM this evening/...
as of 1254 PM EDT Thursday...overall forecast in good shape with
respect to previous idea of slower clearing on the clouds and
cooler temperatures. Highs will generally be in the upper 40s to
upper 50s with some lower 60s over southeast Vermont where the sun
was out earlier this morning. Isolated showers have come to an end
and have removed from the forecast. Rest of grids remain unchanged.
Short term /7 PM this evening through Saturday/...
as of 423 am EDT Thursday...nearly ideal conditions for a
widespread frost/freeze event tonight as strengthening high
pressure settles southeastward across the region from Ontario and
southwestern Quebec. Air mass very dry with 1000-500mb relative humidity values
dropping below 30 percent. Anticipate clear skies with light
winds. Freeze watch has been upgraded to freeze warning for the
St. Lawrence Valley and northern Adirondacks in New York...as well as
north central and northeast Vermont. Min temperatures in the warning area
expected to range from the middle 20s to the lower 30s. Frost
advisories issued for south-central Vermont and all of Champlain
Valley except Grand Isle County. Min temperatures in the advisory area
mainly between 32-36f. A bit milder in Grand Isle County
(champlain islands) due moderating influence of the warmer lake
waters. The freeze will be climatologically early by 1-2 weeks in
many areas of central and eastern Vermont as well as for the St.
Lawrence Valley. Will also see some patchy fog late...mainly in
the Connecticut valley region.
Once any fog dissipates Friday morning...expect plenty of sunshine
as high pressure remains in control of north country weather. The
center of the high will drift southeast into the Gulf of Maine by
Friday evening. This will allow for a light return southerly flow
of air to develop during the afternoon. 850 mb temperatures moderate to
between +3 and +5 c by evening. But the cold start to the day will
make it difficult for temperatures to top 60 degrees in most
areas...despite the abundance of sunshine.
Surface high elongates from southwest to northeast as it slides
slowly off the East Coast Friday night through Saturday.
Temperatures Friday night will not be nearly as chilly as tonight
in most areas...thanks to the combination of increasing southerly
flow and some clouds moving in from the west. Expect lows in the
40s in the St. Lawrence and Champlain valleys and upper 30s
elsewhere. Some locally cooler readings expected east of the Green
Mountains where winds will become light and variable as low levels
decouple. Also expect some patchy fog in same areas.
Partly to mostly cloudy skies expected on Saturday...as warm front
associated with disturbance in flow aloft moves across the region.
Low level moisture limited and forcing weak however...so chances for
showers appear rather low. Have continued with 20-30 per chance
chance of light showers across northern areas. 850 mb temperatures climb to
between +11 and +14c...so it will be milder even with the clouds.
Expect highs in the upper 60s and lower 70s...along with rather
brisk south to southwest winds.
Long term /Saturday night through Wednesday/...
as of 400 am EDT Thursday...very little overall change from
previous forecaster thinking as medium range guidance remains in
good agreement in regards to the synoptic pattern during the
Long term forecast starts out dry for Saturday night with the btv
County Warning Area entrenched in the warm sector of a developing surface low
just north of the Great Lakes. Should be a pretty mild night
under partly cloudy skies and a modest southerly wind with lows
ranging through the 50s area-wide to low 60s in the Champlain and
St. Lawrence valleys. By Sunday morning...low tracks northeast
through south-central Quebec dragging the attending cold front
through the north country. GFS and European model (ecmwf) remain in good agreement
from previous runs in regards to frontal passage timing...and feel
confident we'll see a good 6-hour period of light rain at any one
location as the front traverses the area. Bets guess at timing
right now looks like 12-18z across northern New York...Champlain
Valley 18-00z...and eastern Vermont 00-06z Sunday night.
Cold front shifts east of the region Monday morning but the
trailing upper trough continues to dig into the middle-Atlantic and
northeast states with a secondary shortwave diving southeastward
Monday night into Tuesday. Best available low/middle level moisture
is east of the btv County Warning Area with the front but can't rule out a few
showers as the trough passes and flow turns to the northwest. We
could even see the first snowflakes of the season across the
higher terrain of far northern Vermont (jay peak to mansfield) as
prognosticated 850mb temperatures off the GFS fall below freezing and 500-1000mb
thickness dip below 540dm. European model (ecmwf) is slightly warmer so we'll
see...but fall will definitely be in the air with the trend of
below normal temperatures continuing.
Aviation /18z Thursday through Tuesday/...
through 18z Friday...cold front just about south of the area. In
its wake is a roughly 100 Mile wide band of clouds with bases in
the 2000-4000ft range. So some MVFR conditions exist, but the
trend has been for the ceilings to slowly rise and satellite
imagery shows increasing breaks developing. Thus expect by 22z VFR
conditions will be everywhere. The clouds will dissipate by middle
evening. Unlike other nights, we are not expected a lot of fog.
Could be some patchy valley fog down in the CT River Valley (so if
we did a taf for Springfield/vsf, it would show ifr), but for our
official taf sites, fog is not expected. Just frost. Friday will
be VFR thanks to high pressure overhead. Light surface winds as well.
Outlook 18z Friday through Tuesday...
18z Friday through 12z Sunday...mainly VFR under high pressure.
IFR in late night fog mainly for kslk and kmpv. Increasing south
winds Friday night and Saturday. Some gusts in excess of 25kt
possible. Low level wind shear also a possibility due to stronger winds aloft.
12z Sunday through 12z Monday...VFR trending to MVFR in showers
from west to east as a cold front tracks through the region.
12z Monday Onward...likely VFR, though a mix of a few showers and
clouds could produce some MVFR.
as of 150 PM EDT Wednesday...
Following are the record lows for Friday morning sept 19th. Given
the expected blast of chilly air, we may be approaching records at
Montana Mansfield (mmnv1)...24f 1979
Rutland (rutv1)........27f 1990
Montpelier (mpv).......29f 1959
St Johnsbury (sjbv1)...29f 1943
Massena (mss)..........30f 2008
Burlington (btv).......32f 1959
Vermont...freeze warning from 1 am to 8 am EDT Friday for vtz003-004-
Frost advisory from 1 am to 8 am EDT Friday for vtz002-005-009-
New York...freeze warning from 1 am to 8 am EDT Friday for nyz026-027-
Frost advisory from 1 am to 8 am EDT Friday for nyz028-035.