Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service Burlington Vermont
734 PM EDT Wednesday Apr 23 2014

Synopsis...
high pressure will slowly build into the north country by Thursday
with clearing skies and near normal temperatures expected. The next
chance for showers will be Friday night into Saturday along with the
arrival of cooler air for the weekend. A few mountains snow showers
will be possible on Saturday night and again on Sunday night...but
only minor accumulation anticipated.

&&

Near term /until 6 am Thursday morning/...
as of 725 PM EDT Wednesday...going forecast in good shape. Only
minor changes with latest update...mainly to input latest
observational data into grids. We remain under influence of upper
trough...with cyclonic northwest flow continuing. Clearing line
approaching Saint Lawrence valley at this time. Expect it to
advance slowly eastward tonight...with threat of any rain/snow
showers coming to an end across northern New York...but chances
continuing across northern Green Mountains as forecast indicates.
Any precipitation amounts on the light side. No changes to temperature forecasts
for the overnight.

Previous discussion...
water vapor shows middle/upper level trough across the NE Continental U.S. Slowly
lifting toward eastern Canada overnight...with large area of
subsidence developing across the central Great Lakes. This will slowly
move toward our region after midnight with some clring across our western
County Warning Area. Meanwhile...the combination of cyclonic follow and embedded 500 mb
vorts will result in some light rain/snow showers across the mountains
tonight. Will use the btv 4km and rap 13 to highlight upslope precipitation
this evening...but overall quantitative precipitation forecast/snowfall will be light with only
accumulation above 2000 feet. Thinking quantitative precipitation forecast will be a couple hundredths
of an inch at best. Will mention chance to likely probability of precipitation across the
northern dacks and northern/central Green Mountains in Vermont through
06z...then taper off toward morning. Soundings show good mixing
tonight and plenty of leftover relative humidity between surface and 700mb resulting in
lots of clouds...so thinking lows will range from upper 20s mountains/slk
to M/u 30s warmer valleys. I realize guidance for slk is around
20f...but this seems way too cold based on clouds/winds...and current
surface dewpoints in the m30s.

&&

Short term /6 am Thursday morning through Friday night/...
as of 340 PM EDT Wednesday...main forecast concerns will be fire weather
related on Thursday...followed by arrival of precipitation late Friday.
See fire weather section below for details regarding winds/rh's and
recent dry spell across parts of the region. The combination of
departing surface low pressure and building high pressure will result in breezy
to gusty west to northwest winds of 15 to 25 miles per hour with localized
gusty to 35 miles per hour. Soundings show top of the mixed layer around 35
knots on Thursday with bottom layer winds around 30
knots...supporting this gusty winds. Still thinking some clouds will
linger across the northern/central mountains of Vermont...including the nek on
Thursday...but clring skies will develop by midday associated with surface
high pressure. Prognosticated 850 mb temperatures between -2c and -4c...support highs only
in the M/u 40s mountains to l/m50s warmer valleys on Thursday. The
combination of clear skies and calm winds with surface high pressure
overhead will result in cool temperatures Thursday night. Lows will range in the
20s colder mountain valleys to l/M 30s warmer/wider cpv/slv valleys.

Middle/upper level ridge breaks down on Friday into Friday night with
next system approaching the NE Continental U.S.. feel initial short wave energy and
associated ribbon of 850 to 500mb relative humidity will dissipate as it encounter
ridge/dry air across our region. Will mention low chance probability of precipitation late Friday
afternoon across our western County Warning Area and increase probability of precipitation overnight ahead of
better dynamics. Temperatures will warm to near normal on Friday and stay
mainly in the 40s Friday night with the clouds and developing
southerly winds.

&&

Long term /Saturday through Wednesday/...
as of 330 PM EDT Wednesday...looking at unsettled weather for the
upcoming weekend as upper level low pressure moving through the
Great Lakes Friday night closes off over the north country
Saturday morning...and shifts offshore Sunday afternoon. The
result will be periods of showers through Saturday night...with
cloudy...cool and brisk conditions for Sunday. Thereafter...blocking
pattern looks to setup across the Continental U.S. With aforementioned closed
low stalling off the eastern Seaboard... another closed low
developing over the central rockies...and a highly amplified ridge
in-between. While we should see generally dry conditions through
this period for next Monday through Wednesday as the entire setup
slowly shifts eastward...if and when the ridge breaks down the
potential exists for a multi- day rain event as The Rockies low
shifts east and taps into rich Gulf moisture. Temperatures will be
generally near normal with highs in the 50s and lows in the 30s
and 40s.

&&

Aviation /00z Thursday through Monday/...
through 00z Friday...bkn/ovc VFR ceilings and visibilities to prevail
through early morning Thursday before ceilings scatter out later
in the day. Sustained north winds 10-12 kts with 20-28 knots gusts
dropping off over the next couple of hours. However...anticipate
gusts to pick back up again by around 12-14z as mixing commences.

Outlook 00z Friday through Monday...

00z Friday through 00z Sat...VFR under high pressure. Continued gusts from
the northwest 00z through 12z Friday.

00z Sat through 00z Monday...mainly VFR with chance of MVFR showers
associated with a weak low passage.

Monday...mainly VFR under scattered-broken skies.

&&

Fire weather...
fire weather concerns increase on Thursday for elevations below
1500 feet across southern Vermont...due to the combination of the recent
dry spell...expected breezy winds...and low min relative humidity values.

The last measurable precipitation at Springfield Vermont ASOS was
4/15/14...when 0.70" occurred...since then only a trace of precipitation
has been observed. Similar conditions have been noted at
Rutland AWOS site. This has resulted in significant drying of the
fine fuels per local Forest contacts below 1500 feet...where green
up has not occurred. Meanwhile...above 1500 feet most of the fine
fuels and Leaf litter is compressed from recent snow pack or still
wet. Most of central/northern Vermont mountains and parts of northern New York
have received measurable precipitation over the past 2 to 5 days or snow
pack is still on the ground above 2000 feet...resulting in limited
threat.

Breezy west to northwest winds of 15 to 25 miles per hour with gusts to
30 miles per hour are expected across the higher terrain...parts of the CT River
Valley...and Champlain Valley on Thursday. In addition...min afternoon relative humidity
values will drop between 25% and 35% between 1 PM and 5pm on Thursday across
this area...with isolated readings of 20% near Springfield Vermont
possible.

These conditions combined with the overall drying of
grasses...twigs...and debris such as dead leaves from last fall and
you will want to pay close attention to any outdoor burning you may
be attempting on Thursday. Monitor weather conditions...do not leave
your brush or debris pile unattended...and heed any advice from your
local fire Warden.

Given the small geographical area with favorable fuel conditions and
marginal fire weather parameters...no Fire Weather Watch will be
issued with this package...but will highlight in severe weather potential statement product.

&&

Btv watches/warnings/advisories...
Vermont...none.
New York...none.

&&

$$
Synopsis...Taber
near term...rjs/Taber
short term...Taber
long term...lahiff
aviation...lahiff/loconto
fire weather...Taber