Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
648 am EST Monday Nov 24 2014
an area of rain will move through the region through the morning
hours along a warm front lifting south to north. High temperatures
today will be well above normal with readings in the upper 50s to
lower 60s. In the coming days however temperatures will begin a
downward slide to seasonal normals as cooler air moves in from the
north and west. A storm system moving up the Atlantic coast late
Wednesday will bring accumulating snows mainly to southern Vermont,
with lesser amounts in the Champlain Valley and Adirondacks. Impacts
on travel will be felt late Wednesday through Thanksgiving morning
in southern Vermont into the southeast portion of New York and
across southern New England.
Near term /until 7 PM this evening/...
as of 626 am EST Monday...update to the forecast to adjust
rain timing and blend in observed weather. Forecast unfolding as
planned, rain covering most all of the area except just now moving
in to far northeast Vermont, and beginning its exit of western St.
Lawrence County. Trend of rain ending west to east will continue
through the morning. Relative min in probability of precipitation early afternoon, then
come back up to chance with low level convergence along wind
shift/frontal boundary moving through later today.
Full latitude trough at 500 mb over the central US with
southwesterly flow in the east riding up over a western Atlantic
ridge. Shortwave trough moving out of Ohio Valley northeast into
eastern Great Lakes with surface warm front trailing along into
our forecast area through this morning. Temperatures quite
warm...in the upper 50s to lower 60s supported by surge of warm
southerly flow bringing 925 mb temperatures in the near 13 c. Speaking of
southerly flow...boundary layer winds quite strong with a low
level jet over 60 knots through midday. Do not believe winds will
be able to mix to surface however as they remain above the low
level inversion and rainfall tends to stabilize lowest levels and
prevent wind from mixing. Mountain summits & highest ridgetops
will see stronger winds however no population up there to warrant
Short term /7 PM this evening through Wednesday night/...
as of 327 am EST Monday...after passage of warm front low level
frontal inversion is eliminated and more mixing occurs from
surface through boundary layer. Stronger winds do mix down,
especially northern New York, however low level jet diminishes
somewhat during this time period. Northern New York along
northwest slopes of the Adirondacks will see sustained winds
around 25 kts with in the middle 30s kts with widespread 15-25 kts
elsewhere. Very near Wind Advisory levels and may need to issue
advisory in upcoming forecast.
Cooling trend begins in the short term period. Low level winds
turn southwesterly, and approaching upper low from the west starts
a trend of lowering heights and cooling of the air column.
Relative quiet period into Wednesday with southwest flow over the
region and some lake effect precipitation off Eastern Lake Ontario into
the northwest Adirondacks. Starts off warm enough for rain then
eventually cools to snow late Tuesday before ending Tuesday night.
Surface high pressure builds in late Tuesday and early Wednesday,
then coastal low begins to make presence felt.
GFS/European model (ecmwf) beginning to align a little better than previous runs
however general trends of GFS being further east and faster with
the surface low continues. GFS track would keep forecast area in
the colder air with less forecast precipitation totals, while
European model (ecmwf) is wetter but warmer solution with possibility of rain mixed
in at some point. Timing would be precipitation beginning after 18z
Wednesday with bulk of precipitation Wednesday night. Believe it
would be nearly all snow as temperatures from 925 mb upward below
freezing. Surface temperatures above freezing at onset of precip, and
western European model (ecmwf) could throw some warmer air in. However with cooling
aloft throughout the life of the storm and wet bulb cooling of
near surface layer expect mainly snow.
Using model blend of quantitative precipitation forecast came up with a half inch or more in the
lower CT River Valley and southern tier of Vermont counties and a
quarter inch or less in Champlain Valley and northwest. Resulting
snowfall using a Standard 13 to 1 ratio puts southern Vermont
right at Winter Storm Watch criteria. However not up to the 50%
certainty to warrant a watch given continued model differences and
run to run changes between each. Will wait another forecast cycle
for a headline decision which will also allow incorporation of 12z
Thursday-00z Friday quantitative precipitation forecast/snowfall forecast that would encompass entire
Long term /Thursday through Sunday/...
as of 354 am EST Sunday...low pressure will be moving away from
the region on Thanksgiving with upper level trough passing by
evening. Expecting some lingering light snow early tapering to
snow showers or flurries which will continue periodically
Thanksgiving night. Light accumulations are expected mainly in the
northern mountains and nek. Temperatures either side of freezing on
Thanksgiving day dropping into the teens to around 20 at night.
Northwest flow on Friday may bring a few mountain snow showers or
flurries before a ridge of high pressure moves by Friday night. It
will be chilly with high temperatures mainly in the 20s and over night
lows in teens, perhaps a bit colder depending on cloud cover.
A warm then cold front passages are likely Saturday night into
Sunday with timing and temperature differences noted in the
models. This will dictate whether the showers are rain or snow but kept
close to the blend but temperatures could swing a bit milder it would be
more in the way of rain showers, especially in the valleys. Highs
in the 30s and lows in the 20s.
Aviation /12z Monday through Friday/...
through 12z Tuesday...threat of low level wind shear through the morning with
winds 2000-4000ft of 45-70kt. A large cloud and precipitation
shield associated with a warm front will be passing through this
morning ending from west to east. Mainly MVFR ceilings and
visibilities will improve to VFR by 18z...but ceilings may linger
in the MVFR category on and off in the mountains. South and
southeast 10 to 20 knots gusting locally to 30 kts. Winds will
gradually back around to the south and southwest during the
afternoon and evening and some gusts of 30 to 40 kts possible as a
cold front makes it way into northern New York. Could be a scattered
shower but left out for now.
Outlook 12z Tuesday through Friday...
12z Tuesday - 00z Thursday...generally VFR with MVFR/IFR ceilings/visible
in lake effect snow possible at slk.
00z Thursday - 00z Friday...low pressure moves NE just off the
New England coast with IFR in snow/snow showers.
00z Friday - 00z Sat...mainly MVFR with local IFR in snow showers.
a lake Wind Advisory in effect today as winds will be increasing
to 25 to 35 knots with waves 3 to 5 feet on average. Low pressure
will track up through the Great Lakes this morning with a warm
front bringing rain to the lake mainly this morning, then only a
chance of a shower for the rest of the day. A cold front will
bring a gradual shift to southwest tonight when the strongest
winds are expected. Southwest winds will gradually subside during