Scientific Forecaster Discussion
fxus61 kbtv 190338
Area forecast discussion
National Weather Service Burlington Vermont
1038 PM EST Sat Nov 18 2017
strong low pressure will pass through the region tonight into
Sunday with widespread rainfall and milder temperatures. Rain
will taper to snow showers on Sunday afternoon as much colder
air surges back into the area along with gusty winds. The
general weather pattern next week will feature mainly seasonable
weather. There will be a chance of a few rain or snow showers
Wednesday, but otherwise it looks mostly dry for the
Near term /through Sunday night/...
as of 1032 PM EST Saturday...leading band of isentropic
lift/warm advection associated precipitation has lifted across
nrn New York and central/northern Vermont this evening. Mainly a cold rain
across the north country, but a few pockets of temps near
freezing in the deeper Mad River valley and adjacent valleys of
central Vermont yielding some localized/brief freezing rain. Had one
such report from Waitsfield with the onset of pcpn. Likewise,
some of the valleys of nern Vermont have temps right at 32f. Issued a
Special Weather Statement to cover any brief/localized freezing
rain. Overall warming trend expected overnight with S-southeast winds,
so winter driving conditions generally not expected overnight.
Have seen 0.10" rainfall thus far at btv. A bit of a lull in the
precipitation next few hours, but parent sfc low near kbuf
continues to deepen (985mb at 03z), and will be associated with
next wave of rainfall during the pre-dawn hrs. Should see an
additional one to three tenths of an inch in most locations by
12z. Made some minor changes to temperatures and precipitation
type based on current observational trends, but overall
expectations remain on track. The previous discussion follows.
Previous discussion...no big changes in the forecast after
review of the 12z guidance. Deepening surface low in western
Ohio is already down to about 988mb as of mid afternoon, and
will continue to strengthen as it tracks to the northeast. All
guidance are pretty close on track and intensity, so we expect
the center of the low to track right up the St Lawrence Valley
and by 12z Sunday, likely sitting nearly on top of Massena with
a pressure somewhere in the 978-982mb range. The low will push
rapidly to the northeast of the region Sunday, pushing a strong
cold front through the area. Rain overspreads the area tonight,
becoming more showery in nature tomorrow morning. The showers
will transition to snow showers and as moisture pulls away, the
coverage will take on an orographic look and be concentrated
across the higher terrain of the Adirondacks and northern
greens. A tight pressure gradient will also develop as the low
departs, resulting in a gusty west- northwest wind area wide.
Regarding various elements of the forecast, here are a few items
Temperatures: it's a tricky forecast, and prone to large errors.
In general, southerly winds will be resulting in steadily
warming temperatures for most of the region overnight. Sunday's
high temperatures will occur during the morning, with
temperatures falling all afternoon to the upper 20s to low 30s
by late day. Most of US will be in the 40s overnight. There is
actually a couple of models that indicate portions of the
Champlain Valley will rise into the lower 50s after midnight as
a southerly low level jet develops. Wasn't quite that bold in
the forecast, but we can't rule it out. It will be harder to
scour out the colder air in eastern VT, but still everywhere
will be above freezing. The immediate St Lawrence River valley
region will not see those southerly winds. Instead, a cold
northeast wind will persist as is common in situations with lows
coming up the valley. This will keep temperatures there in the
low/mid 30s all night, so when the cold front moves through,
there won't be much of a temperature change.
Winds: southerly winds will increase overnight, at times a
little breezy in the Champlain Valley. As mentioned above, a
brisk northeast wind will persist in the St Lawrence Valley. The
primary winds will be after the cold front passes. Strong cold
air advection will keep the boundary layer well mixed. With
winds around 40-45kts at 850mb, some of that wind will come down
to the surface at times. Models today are a smidge weaker with
the winds than yesterday, so thinking 35-40 mph gusts will be
common. Could be some downslope enhancement, especially on the
eastern side of the Adirondacks and Green Mountains for some
local gusts Sunday afternoon around 45 mph. At this time these
winds will be just below our Wind Advisory threshold, so won't
raise those headlines. However later forecasts will have to
monitor that potential.
Precipitation type: strong warming aloft this evening and
overnight will mean rain. Can't rule out isolated sleet pellet
or two at the onset of the precipitation this evening as a dry
boundary layer helps with evaporative cooling. There will be a
quick crash of temperatures aloft and at the surface with the
cold front passage, so as it moves through, any rain showers
around will transition fairly quickly to snow. By late Sunday,
any precipitation will be in the form of snow showers.
Snowfall accumulations: not looking at much in the way of
accumulation, as by the time the precipitation turns to snow,
the bulk of the deep moisture will be pulling out. Expecting
perhaps up to 1" at elevations from 800ft to 1800 ft. Maybe
2-3" or so at elevations above that. Nothing more than a flurry
or light dusting at lower elevations.
Short term /Monday through Monday night/...
as of 154 PM EST Saturday...deep cold trof rotating out of area
during this period with building heights and zonal flow and
surface ridging while the main surface high is located along the
Primarily dry and unseasonably cool with gusty northwest winds of sun-sun
ngt gradually diminishing and shifting W-WSW. Highs 25-33. Return
flow Monday night means not as cold as sun ngt-Mon morning with the
exception of eastern Vermont and lows in the 20s with teens in NE Vermont and
deep Adirondacks vlys.
Long term /Tuesday through Saturday/...
as of 154 PM EST Saturday...primarily a very broad cyclonic
flow pattern for the period with very minor disturbances and
slight roller coaster of temperatures but largely below normal.
There is an outside threat of a coastal storm Wed-Wed ngt but
most current indications are keeping this a mid-Atlantic and
then out to sea storm with no impacts for our area but still
Worth monitoring for the next few days.
Tuesday: high pressure sliding offshore for a return flow ahead of
northern stream shortwave for moderating temperatures in the 40s.
Northern shortwave and cold front move across area Tue ngt and
largely exit by Wednesday. This will bring rain to mixed rain/snow
showers and colder air once again.
Wednesday: cold front exiting region, although we still must look to
our south and model trends about possible coastal. Currently,
exiting drier conditions with some mountain snow showers possible
with temperatures in the 30s/40.
Thanksgiving: quiet with surface high in control but the eventual
approach of another northern stream shortwave by Thursday night.
Currently dry with temperatures in the 30s.
Thursday night/friday: much of the energy with northern stream
shortwave is in Canada but can't rule out some isold/sct snow
showers, especially in the mountains. Lows in the 20s and highs in
the 30s, a tad milder than Turkey day.
Friday night/saturday: we return to a more zonal flow with another
minor shortwave and surface reflection moving along the Great Lakes
and international border with some decent warm-air advection
ahead of it for light snow/snow showers Friday night and
scattered rain/snow showers on Saturday with temperatures in the
Aviation /04z Sunday through Thursday/...
through 00z Monday...expect a mix of MVFR/IFR as widespread rain
moves into the region this evening. All terminals except mpv
should see rainfall by 01z with MVFR ceilings lowering to
between 1000-2000 feet overnight. As a cold front moves closer
anticipate some periods of IFR at slk/btv with a more prolonged
period of LIFR at mss under pressure driven northeast winds.
After the front pushes across the region between 13-16z expect a
sharp wind shift with gusty winds on the back side of the
front. Winds will shift to northwest and gust between 20-30kts.
With cold air building in the rain will abruptly switch to snow
behind the front so there could be periods of IFR snow at
mss/slk in the morning hours Sunday.
Sunday night: VFR. Windy with gusts to 30 kt. Chance shsn.
Monday: VFR. No sig weather.
Monday night: mainly VFR, with local MVFR possible. No sig weather.
Tuesday: VFR. No sig weather.
Tuesday night: mainly VFR, with local MVFR possible. Slight
chance shra, slight chance shsn.
Wednesday: VFR. Chance shra, chance shsn.
Wednesday night: VFR. Slight chance shsn.
Thanksgiving day: VFR. Slight chance shsn.
as of 245 PM EST Saturday...a lake Wind Advisory is in effect
for overnight and into Sunday. Southerly winds overnight will
increase to 20-30 knots. A strong cold front will move across
the lake during the mid to late morning on Sunday. Winds will
quickly switch from south to west with the frontal passage and
remain strong and gusty. Some gusts over 35 knots are possible
during the afternoon. These winds will result in wave heights of
at least 2 to 4 feet, producing very choppy conditions. These
conditions may prove hazardous to those operating small craft