Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1029 am EDT sun Sep 21 2014
showers will develop from west to east across the north country
today as low pressure moving through central Quebec drags a cold
front through the region. The front clears the region tonight with
precipitation coming to an end after midnight with unseasonably cool
temperatures expected for Monday. Below normal temperatures will
be brief however as warmer air and dry conditions return for much
of next week under a large area of high pressure.
Near term /until 11 PM this evening/...
as of 1023 am EDT Sunday...cloud/pop/weather forecast in really
good shape with no changes need there on this update. Only blended
temperatures into observed and populated this afternoon and maximum
temperatures with lav. This raised afternoon highs in the clear areas
into the middle 70s...mainly central/southern Champlain Valley and
Vermont. New York side under the clouds and nearer the rain should
see temperatures level off. In fact Massena hit 70 earlier and has sinced
dropped to 68 at 14z with light rain. Radar loop showing swath of
rain moving up St. Lawrence Valley associated with a middle level
mesoscale-vorticity center. Based on radar trends and hrr model
reflectivity this area of rain will progress on northeast but stay
mainly in northern New York. This afternoon as cold front pushes
east rain area will move west to east. Present pop forecast has
this covered well with likely probability of precipitation in New York through 18z then
spreading in to Vermont.
Previous discussion...forecast remains largely on track for today
as low pressure moving through central Quebec will drag a cold
front across the north country through this evening. Frontal
boundary and shortwave energy are still far west of the region
this morning...so only real change to previous forecast thinking
was to delay the onset of rain by a few hours. Some uncertainty
exists as to how much rainfall we see as latest rap/hrrr forecasts
show moisture thinning as it approaches the region...but NAM/GFS
still show a fairly solid line moving through. Consensus is that
we'll see a 3-hour window of showers at any one location...with
overall quantitative precipitation forecast amounts a quarter to half inch by midnight. Front
clears the forecast area after midnight with the middle/upper level
flow turning northwesterly Post frontal passage. This combined
with some lingering low level moisture will support some upslope
showers across the higher terrain...but feel this will be short-
lived as very dry air from 500-700mb advects into the region by
For temperatures...with early arrival of precipitation across northern New York
highs will be the coolest across the region and run generally in
the upper 60s to low 70s. Meanwhile from the Champlain Valley
eastward where we should see some sun this morning into early
afternoon...highs will bump up into the middle to maybe upper 70s.
Likewise for tonight...lows across northern New York will be
coldest in the 40s...while across Vermont 50s.
Short term /11 PM this evening through Tuesday/...
as of 405 am EDT Sunday...coolest day of the upcoming week comes
Monday with cold air advection across the region from the outgoing
low and incoming high. Any morning upslope showers across the
higher terrain should taper off by middle-day with middle-level dry air
winning over the low level moisture. Highs will run quite a bit
below normal ranging through the 50s...but with a modest north
wind throughout the day it'll feel like it's in the 40s at times.
Clouds begin to clear Monday night as an upper level ridge and
surface high pressure over the central Continental U.S. Begin to shift
eastward in the Great Lakes. This high shifts right overhead
Tuesday...with the upper flow remaining out of the northwest
supporting some scattered diurnal cumulus formation...but no
precipitation is expected. Lows Monday night continue to run on the cool
side of normal in the upper 30s to middle 40s...but highs rebound on
Tuesday pushing into the 60s area-wide.
Long term /Tuesday night through Saturday/...
as of 242 am EDT Sunday...no significant changes from the previous
forecast. A deep-layer ridge will develop and move eastward from
the Great Lakes Tuesday night...and remain in place across the
northeast Continental U.S. Through next weekend. Only departure from previous
forecast is that the 00z GFS indicates that a backdoor cold front
may push southward across northern Vermont during Thursday
night/Friday morning. This idea has less support from the 00z
European model (ecmwf)...which keeps a stronger middle-level ridge in place. Based on
the 00z GFS...there may be a period of some cloudiness with the
front...but it appears overall that precipitation is unlikely. Maintained
a dry forecast for the entire extended forecast period. Temperatures
will generally be 6-10 degrees above climatology for daytime
highs...with readings in the upper 60s to middle 70s for valley
locations. Lows will be coolest Tuesday night (upr 30s to middle
40s)...and then generally in the middle 40s to lower 50s thereafter.
Mostly clear skies and light winds may lead to some nocturnal fog
in the favored river valleys each night...generally between
04-12z. All in all...a delightful stretch of weather as we begin
astronomical fall this week.
Aviation /15z Sunday through Thursday/...
through 12z Monday...VFR ceilings expected through this morning
and into the middle-afternoon hours at the taf sites. Surface winds
will remain moderately strong from the south and southwest
downstream of the frontal system crossing the Great Lakes. Have
included gusts up to 28 kts at btv through 16z. Front begins to
bring showers to mss/slk after 18z...and closer to 23-00z at
pbg/btv...and near 00-01z rut/mpv. Anticipate some MVFR ceilings
both with the shower activity and with potential lower
ceilings/visibility behind the front with a westerly wind shift and areas of
br during the overnight.
Outlook 12z Monday through Thursday...isolated to scattered
showers are possible over the mountains during the day
Monday...with periods of MVFR ceilings possible at slk/mpv with
hir terrain obscured. Generally VFR elsewhere. Monday night
Onward...dry with building high pressure. Generally VFR...except
LIFR/vlifr nocturnal fog possible slk/mpv 06-12z each morning Tuesday-
as of 405 am Sunday...strong south winds will continue across Lake
Champlain today as a cold front tracks through the region this
afternoon. 20 to 30 knots this morning ahead of the front will
weaken to 15 to 25 knots this afternoon...and further to 5 to 10
knots after sunset. Waves of 3 to 5 feet this morning will slowly
subside this afternoon in response. A lake Wind Advisory remains
in effect through today.