Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
346 PM EST Tuesday Jan 27 2015
a strong coastal low pressure east of Cape Cod will
slowly move away from the region tonight...with areas of snow
tapering off to scattered flurries by Wednesday morning. In
addition...gusty north winds will slowly decrease as surface high
pressure builds into the region. A fast moving clipper like system
will impact the north country late Thursday into Friday with another
round of light accumulating snow likely. Temperatures will start
below normal...but warm to near normal levels by Thursday.
Near term /until 6 am Wednesday morning/...
as of 345 PM EST Tuesday...Ave cancelled Winter Storm Warning and
replaced with Winter Weather Advisory for snow and blowing snow.
Also...expanded advisory to cover parts of the Champlain and
western slopes for the combination snow and blowing snow through
the evening commute. Expecting a difficult evening commute across
most the region. Btv picked up 3 inches of snow in just several
hours under this band of heavy snow this afternoon. Expecting additional
accumulations of 1 to 3 with localized higher amounts under this
narrow mesoscale band of moderate snow across portions of the Champlain
and western slopes.
Forecast challenge tonight will be areal coverage/intensity of snow through
midnight...especially for the Champlain Valley and parts of Green
Mountains current water vapor shows deep closed cyclonic circulation just
east of Cape Cod this afternoon...with several band of middle/upper level
moisture rotating back toward our County Warning Area. Water vapor and rap shows
this middle level moisture and elongated 500 mb vorticity maximum will become
stationary across the Champlain Valley/central Vermont this
aftn/evening...with occasional snow lingering through the evening hours.
This support aloft...combined with favorable northerly follow will
enhance convergence on the eastern side of the Champlain
Valley...supporting light snow through 06z...before tapering off to
flurries. In addition...NAM Froude number shows blocked follow with
values <0... enhanced snowfall along and upstream of
the Green Mountains into the Champlain Valley. Will try to show this detail
in the grids and increase the snowfall amounts slightly across this
region...thinking between 1 and 4 inches...with isolated higher amounts
possible. Elsewhere...areal coverage of middle level moisture decreases
rapidly this aftn/evening...and additional snowfall will be limited.
This is already supported by radar showing large hole of no precipitation
across most of the CT River Valley and nek of Vermont. Additional snowfall
will be a dusting to an inch or two possible in these areas...with
only flurries for the Saint Lawrence valley/western dacks.
Also...expect gusty north winds to continue...especially Champlain
Valley with some enhanced channeling...which will cause areas of
blowing and drifting snow. Gusty to 30 miles per hour will be likely through 03z
tonight. Temperatures will remain nearly steady in the single digits
above/blw zero to near 10f most locations.
Short term /6 am Wednesday morning through Thursday night/...
as of 345 PM EST Tuesday...surface high pressure builds across our County Warning Area on
Wednesday...resulting in a slow west to east clring trend. GFS/European model (ecmwf)
still shows some lingering 850 to 500mb relative humidity across our central/eastern
County Warning Area through 15z...before shifting it eastward. Large scale subsidence
and deep drying will result in clring skies by 18z Wednesday. Next fast
moving clipper like system arrives late Thursday into Friday. Latest
guidance tracks this system across our County Warning Area...which will cause a
widespread light snow event. Expecting an advisory level event with
general accumulations of 3 to 5 inches...except slightly higher
amounts of 6 inches in the favorable upslope regions. Temperatures will
rebound to near normal levels after a cold start on Thursday morning.
Long term /Friday through Tuesday/...
as of 335 PM EST Tuesday...an active pattern is quite likely for
the period, with two opportunities for snow and several days with
well below normal temperatures. Given the ongoing weather, and
focus needed on that, I relied rather heavily on a "down the
middle" model blend for most of the forecast period, with only a
few manual modifications. From what I saw, the 12z suite of GFS,
GFS ensemble and European model (ecmwf) were all in the ballpark enough that a
blend should work out pretty good.
Daily details below...
Friday: clipper will be quickly exiting during the day, and as it
moves east of here it should strengthen once it reaches the
"warmer" Atlantic Ocean waters. Net result will be an increase in
northwest winds -- could be gusty at times. Painted in some
20-30mph gusts. These northwest winds will also usher in colder
air as the day GOES on. Definitely a non-diurnal temperature trend
with highs first thing. The middle 20s "warmth" at 8am will end up
in the 5-15f range by evening time. Could have some wind chill
issues to track come Friday/Friday night. On the precipitation
side of things, snow showers first thing in the day will diminish
and be more confined to the mountains by afternoon. In the end,
looks like a solid 3-5" "advisory" level event (locally a bit more
in the northern mountains). Generally clear and cold Friday
night. Sub- zero for everybody!
Saturday: high pressure builds in. Should be sunny, but always
beware of sunny days in mid-winter. That means cold too. 925mb
temperatures down around -20c. Highs 0 to 8f where we live. Brrr.
Warm weather fans will need to look at the sunny skies and pretend
to feel the warmth. Saturday night - another quiet and cold night.
Sub-zero for US all again.
Sunday/monday: fast moving trough in the upper flow will result in
cyclogenesis in the Ohio Valley Sunday, followed by perhaps the
development by Monday of a strong surface low that will track
somewhere just south of here. GFS suggest just south of Long
Island. European model (ecmwf) is a bit farther north and GOES across southern New
England. Have gone ahead and bumped probability of precipitation up to the 50-60% range
for Sunday nite/Monday. Certainly still a lot of uncertainty with
regard to track and intensity. At this point looks like an all
snow event with likely a plowable amount of snow. However, if the
track ends up going a little further north, then we may be looking
at some mixed precipitation issues for parts of the forecast area.
As mentioned, earlier, just went with model blends for
temperatures but above the blends for precipitation chances.
Tuesday: another shot of bitter Arctic air in the wake of the
Sunday/Monday storm. GFS is brutally cold. 925mb temperatures down
to -35c! The raw model surface temperature come Tuesday morning is
-25 to -35f! (Note that MOS turns that into a -3f for btv), and
high temperatures would only be -5 to -15f. The European model (ecmwf) is "much"
warmer -- 925mb temperatures of -20c with it's raw surface
temperatures about -15f in the morning with highs -5 to +5f. At
this point, have made the forecast closer to the ecwmf.
I did want to make the 7th day of the forecast to show a +1c for a
high temperature, just to give some hope to warm weather fans
after days of sub-freezing (< 0c) highs. But alas, it wasn't
Aviation /20z Tuesday through Sunday/...
through 18z Wednesday...confidence on the low side for specific
details in the tafs for now through 03z. Just wanted to get that
out there first.
Currently, conditions range from IFR/LIFR across much of Vermont
to VFR across much of northern New York. Bands of snow are slowly
pushing from east to west across Vermont. In spots, the snow does
briefly result in visibility reductions down to 1/4sm, but in
general it's more like 3/4sm to 1 1/2sm.
Radar trends showing the initial batch of snow is drying up as it
moves toward northern New York. There is uncertainty as to whether
it makes it to slk, though it appears mss will stay VFR. Radar
also showing a "break in the action" developing across the Vermont/New Hampshire
border. It could be that this is a sign that the snow wont last
all that long (6 hours or so) in any spot. However, some guidance
suggests light snow continues all the way to 12z.
Gave it my best shot. In general going with the idea that the bulk
of the moderate snow & lowest visibilities will last up to 20-23z
or so, with diminshing snow through 03z (and MVFR conditions).
After that, VFR should be the rule. May end up needing to amend
forecasts if the radar trends indicate the forecasts need some
Northerly surface winds will remain gusty, especially in the
Champlain Valley. 20-25kts should be common. Perhaps some lower
30kt gusts. These winds will diminish by late afternoon. Though
not explicitly shown in the tafs, minor blowing snow may occur as
From 12z Wednesday Onward, looks like VFR conditions area wide.
Outlook 18z Wednesday through Sunday...
18z Wednesday through 00z Friday...VFR.
00z Friday through 00z Saturday...MVFR/IFR in periods of snow.
00z Saturday Onward...VFR.
as of 122 PM EST Monday...the ktyx 88d Doppler radar located near
Watertown New York will be down at least through Tuesday. This is
due to a pedestal dynamic fault. Electronics technicians have
ordered new parts to fix this problem. However...the new parts
have not arrived as of this time and the ktyx radar will likely
not be restored to service until sometime this week.
Vermont...Winter Weather Advisory until 1 am EST Wednesday for
New York...Winter Weather Advisory until 1 am EST Wednesday for nyz035.
equipment...weather forecast office btv