000
FXUS61 KBTV 221801
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
101 PM EST Mon Jan 22 2018

.SYNOPSIS...
A warm front will lift northeast into the region this afternoon
and evening. Widespread precipitation is expected to develop as
a result. The precipitation will begin as a wintry mix this
afternoon and tonight before changing over to rain during the
morning hours on Tuesday. Light ice accumulations are expected...
especially across portions of northern New York and areas east
of the Green Mountains in Vermont. The warm front moves north of
the area early on Tuesday and rain is expected for all areas as
highs climb into the 40s.

&&

.NEAR TERM /THROUGH TUESDAY/...
As of 1042 AM EST Monday...Minor updates to hourly temperatures
and dewpoints through late afternoon/early evening were made to
account for observational trends. Little adjustments were
needed to our current p-type forecast or expected light snow/ice
accretions at this point. Enjoy your day.

Prior discussion...
Noticing some colder air from Canada making a push southward
this morning...especially across the Saint Lawrence
Valley...northeast New York...and the northern third of Vermont.
Flow aloft will be backing to the southwest as the morning
wears on so at some point the flow of shallow cold air will
stop...but this helps set the stage for mixed precipitation at
the onset of the warm air advection event and places like the
northern Champlain Valley may hold onto mixed precipitation an
hour or two longer before changing over to rain. This subtle
change does not change the overall ice forecast as the warm nose
aloft does not really have an impact until after 00z. But some
areas could see just a bit more snow before the
changeover...generally up to an inch. Rest of forecast remains
unchanged.

Previous Discussion...
Winter Weather Advisory remains in effect for portions of
northern New York and eastern Vermont. Light ice accumulations
are expected to have an impact in these areas.

Weather starts off quiet this morning before a warm front lifts
northeast into the region later in the day and into the first
half of the night. Precipitation really gets going around mid-
afternoon through about midnight before the warm front lifts
north of the border and areas gets into the warm sector. Thermal
profile still supports the idea of mixed precipitation over much
of the area. The only exceptions being southeast Saint Lawrence
County and a good portion of the Champlain Valley where a brief
period of mixed precipitation develops before changing over the
rain as temperatures warm above freezing and remain above
freezing through the night. The real areas of concern are across
the Saint Lawrence Valley...the northern portions of the
northern Adirondacks...and Clinton county in New York and areas
east of the spine of the Green Mountains in Vermont. Low level
cold air holds on in northern New York in response to northeast
winds...but strongest push of the warm layer aloft moves into
this region and thus we continue to expected one to two tenths
of ice accumulation across this areas. A bit more of mixed
precipitation will occur over eastern Vermont and it will not be
until later tonight that more icing develops as thermal profile
becomes more favorable for freezing rain. However...this is all
taking place as warm front lifts north of the border and that is
why we are expecting lower ice accumulation numbers in eastern
Vermont...generally up to a tenth of an inch of ice. Still
enough to cause problems.

Once warm front lifts north of the border after midnight
tonight...area gets in the warm sector and precipitation will
shut down for a bit...especially from the Champlain Valley
eastward. A cold front is still expected to move into the region
on Tuesday and enhance the potential for rain as temperatures
should warm into the 40s across the entire area. Most areas will
see at least a quarter to half inch of rain with higher amounts
possible over southern Vermont. See hydrologic section below for
details on how this will affect river levels and ice jam
potential.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
As of 409 AM EST Monday...As the aforementioned surface low
pressure continues to lift northeast from the St. Lawrence
Valley into southern Quebec and the parent upper trough swings
in behind it, the attending cold front will sweep across the
forecast area Tuesday night with rain changing to snow from west
to east through the pre-dawn hours of Wednesday. Behind the
front west-northwest flow will aid in some lingering snow
showers across the upslope regions of the Adirondacks and
northern Greens through early afternoon, but the deeper valleys
will trend towards drier conditions. A dusting to perhaps 2
inches is possible through Wednesday in the valleys, with 2-5"
across the higher peaks, especially in northern Vermont. Temps
fall sharply behind the front, running in the mid-30s to low-40s
before midnight Wednesday, then plummeting into the teens and
20s by sunrise, and steadily falling further through the day to
widespread low/mid teens by sunset. In addition, a brisk
northwest wind Wednesday will make for wind chills in the single
digits above and below zero.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 409 AM EST Monday...Quieter yet unseasonably colder
conditions develop for the latter half of the work week as
surface high pressure builds in behind the departing low
pressure system, yet the upper trough remains aloft. No
precipitation is expected for Wednesday night through Friday
night, but high temps will be widespread in the teens Thursday,
and struggle to hit the low 20s for Friday. Both Wednesday and
Thursday nights will see a return of single digit lows above and
below zero.

Heading into the weekend the pattern continues to look more active
as we continue to monitor model trends which indicate the potential
for another warmup and mixed precipitation event. The combination of
strong high pressure exiting off the eastern seaboard and a clipper
low moving through southern Ontario will develop strong
south/southwesterly flow across the Appalachian mountains tapping
into rich Gulf moisture ahead of a cold front. Timing continues to
be uncertain in regards to the frontal passage, but trends are
towards a more progressive system with thermal profiles supporting
mainly rain Saturday night through Sunday, possible starting as a
wintry mix, before ending rapidly Sunday night as a mix of rain and
snow. We`ll certainly be ironing out the finer details as the week
goes on so stay tuned.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Through 18Z Tuesday...Widespread MVFR/IFR conditions expected
over the next 24 hours as a combination of a warm front and cold
front cross the region. Initial round of mixed precipitation to
affect terminals in the 18-06Z time frame with a wide variety
of types (-sn/pl/fzra/ra). Warming over time pushes temperatures
above freezing thereafter with remaining precipitation falling
in the form of rain. Southwest LLWS a minor concern overnight at
selected terminals. Surface winds light initially, trending
bodily south/southeasterly overnight into the daylight hours on
Tuesday and occcasionally gusty. Exception at KMSS terminal
where modest northeasterly flow will persist.

Outlook...

Tuesday Night: Mainly VFR, with areas MVFR possible. Chance RA,
Chance SN.
Wednesday: VFR. Slight chance SHSN.
Wednesday Night: Mainly VFR, with local MVFR possible. Slight
chance SHSN.
Thursday: Mainly VFR, with local MVFR possible. NO SIG WX.
Thursday Night: Mainly VFR, with local MVFR possible. NO SIG WX.
Friday: Mainly VFR, with local MVFR possible. NO SIG WX.
Friday Night: VFR. NO SIG WX.
Saturday: Mainly VFR, with areas MVFR possible. Slight chance
SHRA, Slight chance SHSN.

&&

.HYDROLOGY...
As of 409 AM EST Monday...Widespread rainfall is expected
across the area late Monday night and especially on Tuesday.
Current data suggests 36 hour rainfall totals ending at 700 pm
Tuesday will range from 0.50 to 1.00 inch across the area.
Given the substantial loss of snowpack across lower elevations
during last week`s storm, and the fact that the warm-up will be
of lesser magnitude we are not expecting significant ice
movement or water rises on area rivers at this time. This is in
close agreement with NERFC guidance and our latest river forecasts.
Conditions will continue to be monitored closely over the next
48 hours and will be updated if later information suggests a
different scenario than current thinking.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST
     Tuesday for VTZ003-004-006>008-010-012-018-019.
NY...Winter Weather Advisory until 7 AM EST Tuesday for NYZ026>028-
     030-031-034-087.

&&

$$
SYNOPSIS...Evenson
NEAR TERM...Evenson/JMG
SHORT TERM...Lahiff
LONG TERM...Lahiff
AVIATION...JMG
HYDROLOGY...Evenson/JMG

NWS BTV Office Area Forecast Discussion