Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
156 PM EDT Wednesday Mar 12 2014
a powerful late winter storm will bring heavy snow to the north
country by middle day...and will continue through tonight. Strong
north winds will blow and drift snow...and reduce visibilities.
Snow will taper off to mountain snow showers on Thursday. As the
storm system passes temperatures will fall to well below
normal...with lows tonight and Thursday night near zero.
Temperatures will moderate heading into the weekend but remain
Near term /until 11 PM this evening/...
as of 116 PM EDT Wednesday...going forecast in good shape. No
significant changes made. Snowfall coverage and intensity will
continue to increase across the region this afternoon with rates
approaching 1-2 inches per hour this evening. Winds continue to
increase as well with gusts from 20 - 30 miles per hour across northern New
York and the Champlain Valley and 10 - 20 miles per hour elsewhere. This will
create near-blizzard conditions in some areas this afternoon and
evening. Travel will become dangerous as we head into the evening
Previous discussion from 1028 am Wednesday...
forecast playing out well so far. 990 mb low tracking out of the
Ohio Valley will move to a position near New York City this
evening and off the coast of New England overnight...all while
strengthening to 975-980 mb. Snow has overspread the majority of
the area with the exception of far northern Vermont and the Saint
Lawrence valley of New York. Anywhere that's not currently snowing
will be shortly. Heaviest snow still on track for late this
afternoon...this evening...and overnight (21z- 09z)...with bulls-
eye over central Vermont. May even see some thunder-snow this
evening and first half of tonight. Winds will also continue to
increase with gusts from 25 - 35 miles per hour...peaking late this afternoon
in the Saint Lawrence valley and overnight and Thursday morning
elsewhere...especially in the Champlain Valley. This will create
near-blizzard conditions with a whiteout expected at times.
Thinking we fall just short of blizzard criteria (3 hours of 35+
miles per hour wind gusts and 1/4 mile visibility). Snow may hang on longest
in the Champlain Valley Thursday morning with some Champlain
Valley convergence and btv4 WRF forecast Froude numbers below
Previous discussion from 705 am Wednesday...
infrared and water vapor satellite showing shortwave trough moving
through Indiana at 7am EDT. Lightning detection showing convection
continues Indiana with this system after producing overnight
thunderstorms in Missouri and Illinois. Meanwhile a low moving
across the southeastern US will phase with northern stream trough
and aid in northward moisture transport today. Surface front has
moved south of Saint Lawrence valley and is draped across the
Adirondacks...and will provide focus for initial band of snow this
morning. Forecast on track for snow to spread into the northern
Adirondacks first this morning in warm air advection band oriented
east-west across the Adirondacks as overrunning encounters the
surface cold front.
Snow...becoming heavy...will fill in area wide in the afternoon
when surface low moves across southern PA to New York City by
00z. 850 mb low tracks to the north of the surface feature...and
heaviest snowfall in a band along the 850 mb warm front...over
Vermont and northern New York. Warmer low level air will move into
southern Vermont and produce a mix of sleet with the snow this
afternoon...but change to all snow again by nightfall with colder
Long duration period of synoptic scale lift this afternoon
through evening in right entrance and left exit regions of
coupled 250 mb jets. -12 to -18 snow growth zone extends above
700 mb during this time period and coincides with saturated layer
in area of isentropic upglide. Precipitable water in excess of
120 percent across most of the area this afternoon into
evening...and over 200 percent normal in southern Vermont.
Expect band of heaviest snowfall to set up just north of sleet
mix...generally across Essex County New York and central Vermont. 1 1/2
to 2 feet of snow possible in this area.
Little change to going forecast in the near term...loaded up
fresh guidance blend of temperatures. Quantitative precipitation forecast increased small amount this
model run...used a blend of superblend with HPC quantitative precipitation forecast. For snow
amounts used a 10 to 1 ratio through 18z while temperatures near
freezing...then 12 or 13 to 1 afterwards as colder air moves in.
Other part of the story is gusty north to northwest winds behind
the approaching cold front later today into tonight.
Blowing/drifting snow in the forecast in 15-25 miles per hour sustained and
20-30 miles per hour gusts. At this time appears to remain near but below
Some model differences...GFS precipitation is oriented further south
closer to the surface low over southern New England. Per model
diagnostic discussion from National Weather Service weather prediction center the 00z
GFS quantitative precipitation forecast is generally discounted.
Temperatures...steady this morning then falling into the single
digits above and below zero tonight. Mav guidance too cold...and
went with more of a blend of other guidance to minimize mav
Short term /11 PM this evening through Friday/...
as of 431 am EDT Wednesday... surface and upper low passes
by...and northwesterly upslope flow and lingering humidity will
result in mountain snowshowers continuing into Thursday...and
highs in the teens. Surface ridge centers over region around 12z
Friday with shortwave ridging aloft. Subsidence and dry air will
allow for good radiational cooling Thursday night with
temperatures near to below zero. Surface ridge to shift east
during day Friday with return flow in advance of next shortwave
trough. Temperatures to moderate into the low 30s.
Long term /Friday night through Tuesday/...
as of 420 am EDT Wednesday...weak low pressure system passes just
north of our County Warning Area Friday night bringing a chance for snow showers
to the area...especially our northern mountain zones. Snow
showers wind down on Saturday and Saturday night...but as upper
trough crosses the area will still see some mountain snow showers.
Sunday through Monday night will generally be dry with surface
high pressure over the area. Another low will cross north of our
forecast area Tuesday night into Wednesday...bringing another
chance for snow showers to the area. Temperatures will continue
to run below normal through the entire period.
Aviation /18z Wednesday through Monday/...
through 18z Thursday...snow continues with LIFR and vlifr
conditions this afternoon and evening. Snowfall rates around 1 inch
per hour in heavy snow expected during the middle/late afternoon into the
early evening as low pressure system moves across PA toward the
Atlantic. Northerly winds will also impact the region with
sustained speed of 10-20kts affecting northern New York and the
cpv...spreading eastward into southern and central Vermont this evening. Wind
gusts of 20-30kts will result in blsn and reduced visibilities
during the ongoing snow today and tonight.
Conditions will slowly begin to improve after 07z from northwest to
southeast...though snow will probably linger through 12z in northern New York and
into the early afternoon across the Green Mountains winds continue to gust
through the period...up to 30 kts at times.
Outlook 18z Thursday through Monday...
18z Thursday through 00z Friday...improving to VFR conditions at
all taf sites. Northwest winds 10-20 kts.
00z Friday through Sunday...brief MVFR in snow showers Friday
afternoon and evening. Scattered rain and snow showers
Saturday...with brief periods of MVFR/IFR. Frontal passage brings
gusty northwest winds Saturday night into Sunday...20-25 kts at times.
Isolated -shsn...mainly for slk/mpv.
Monday...VFR with high pressure building in at the surface.
Vermont...Winter Storm Warning until 8 PM EDT Thursday for vtz001>012-
New York...Winter Storm Warning until 8 PM EDT Thursday for nyz026>031-