Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
1049 am EDT Sat Apr 18 2015
an upper level trough and weak surface low moving southeast
through southern Canada will bring some scattered rain showers
and possibly a few rumbles of thunder to the north country this
afternoon. High pressure builds into the region tonight and will
bring dry and seasonal conditions through the remainder of the
weekend. A prolonged period of unsettled weather is still expected
next week with widespread rain Monday and Tuesday, followed by on
and off showers through next weekend.
Near term /until 8 PM this evening/...
as of 1048 am EDT Saturday...upstream sounding at cwmw shows
steep middle-level lapse rates but also dry air in the low levels.
Some higher (low-middle 40s) dewpoints in the southwest part of our
area may mix into the low levels resulting in a few hundred j/kg
cape. This instability along with short wave trough moving through
enough to keep showers and a slight chance of thunder going. So
other than a quick update to adjust hourly temperatures and dewpoints,
forecast remains on track.
Previous discussion...forecast remains on track for today
with a potent shortwave trough moving through southern Ontario and
Quebec this morning, tracking just north of the Canadian border
this afternoon. Associated weak surface low and attending cold
front will drop through the north country late morning through
early afternoon with scattered showers developing along the
boundary. Have introduced a slight chance of thunder to the
forecast based on Storm Prediction Center sref calibrated thunderstorm forecasts and some
marginally negative showalters on latest hi-res models, but
overall think this will just amount to a few rumbles hear and
there. In addition, decent cold pool aloft could aid in some
graupel and/or small hail in more convective cells.
Other weather highlight for today will be developing gusty winds
from the southwest this morning shifting to the west/northwest
this afternoon. Gusts in the 20-30 miles per hour range are expected, and
where less precipitation is forecast across southern Vermont
there are some isolated fire weather concerns due to marginal
relative humidity values and dry surface fuels. Anyone planning
open burning today should use caution and plan accordingly as to
mitigate any fires spreading.
Short term /8 PM this evening through Monday/...
as of 500 am EDT Saturday...upper trough shifts east of the
region tonight and is replaced by a strong ridge of high pressure
at the surface and aloft. Winds abate and skies trend clear, with
925-850mb temperatures falling below 0c supporting a chilly night in the
20s and 30s. High pressure centers over the region Sunday for a
dry and seasonal day with highs slightly above normal in the middle
50s to lower 60s.
Dry weather continues into the first half of Sunday night, but
turns south for the later half marking the beginning of a pretty
unsettled stretch of weather likely lasting through all of next
week and into next weekend as a digging upper trough over the
central Continental U.S. Develops into a vertically stacked closed low and
shifts over the northeast. As the surface low takes shape over
the Great Lakes region, a warm front will shift from the Middle-
Atlantic States northeast through the north country late Sunday
night through Monday. Strong southerly flow along the boundary will
tap into rich Gulf moisture with precipitable waters approaching 1" supporting
moderate rainfall which could cause some Hydro issues as snowmelt
continues from deep snowpack across the higher elevations. In
addition, confidence is growing in regards to the potential for
some moderate to strong southeasterly downslope winds along the
western spine of The Greens Monday afternoon as a strong 925-850mb
jet of 40-60kts traverses the area. Right now thinking gusts along
the western slopes of The Greens top out around 40mph which is
sub-advisory, but certainly something to keep an eye on.
Long term /Monday night through Friday/...
as of 331 am EDT...unsettled conditions with relatively cool
temperatures will characterize much of the extended forecast
period. A slow- moving...broad/closed 500mb low across the Great
Lakes Monday night and Tuesday will translate slowly eastward through
the period. Shortwave trough pivoting through the S-southeast periphery of
the cyclonic circulate will bring best middle-level forcing for
ascent 06-18z Tuesday. Have carried 70-80 probability of precipitation for this
period...with quantitative precipitation forecast amts 0.20-0.40" possible late Monday night through
Tuesday morning. Low temperatures should be rather uniform with
low overcast and rainfall...with lows generally in the lower 40s.
High temperatures Tuesday will depend on potential for partial
clearing in middle-level dry slot/subsidence during the afternoon hours.
Have indicated middle-upper 50s...but locally in the lower 50s across
Upper low shifts slowly eastward across New York and northern New England Wed-Fri.
Looking for mostly cloudy conditions with periods of light shower
activity...with coverage potentially enhanced with shallow
instability during the afternoon hours. Generally carried 30-40 probability of precipitation
through the period. Temperatures expected to be slightly below seasonal
averages...with high Wednesday-Friday generally in the low-middle 50s. Overnight
low temperatures generally in the 30s...and locally near to slightly
below freezing in the Adirondacks and far northestern Vermont Wednesday night
and Thursday night.
Aviation /15z Saturday through Wednesday/...
through 12z Sunday...primarily VFR through the period. Compact upper
level trough moving southeastward out of Ontario will bring scattered
showers 16-21z...possibly impacting pbg/btv/mpv. Have carried vcsh
at this point...with local tempo group for MVFR -shra at mpv where
greatest Prospect for shower activity exists. Winds initially
light and variable early this morning...but becoming westerly with
mixing later this morning. It appears flow shifts more northwesterly
10-15kts with gusts to 25kts late in the afternoon into the
evening hours following trough passage and with deep planetary boundary layer mixing.
Winds generally north and diminishing slowly during Saturday
Outlook 12z Sunday through Wednesday...
12z Sunday - 03z Monday...VFR under high pressure.
03z Monday - 00z Wednesday...frontal system brings potential
MVFR/IFR rainfall. Leading warm front will bring first frontal
rain band into the region during Sunday night from SW-NE. Moderately
strong pressure gradient may also result in gusty winds
potentially in excess of 25 kts and low level wind shear during Monday and Monday
00z Wednesday - 00z Thursday...broad upper trough remaining in
place. MVFR possible in scattered showers.