Area Forecast Discussion
Issued by NWS Burlington, VT

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000
FXUS61 KBTV 230029
AFDBTV

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

.SYNOPSIS...
A storm system will bring mixed precipitation and rainfall to
the region tonight into Tuesday along with milder temperatures.
Colder air returns by Tuesday night with lingering light snows
tapering off. Seasonably cold air persists into Friday before
another substantial warmup and mixed precipitation return by
next weekend.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
As of 532 PM EST Monday...Update to expand winter weather
advisory for the Champlain Valley as quick walk upstairs showed
a mixture of snow/sleet and freezing rain here at btv with a
light glaze already developing. Given the band of moderate mixed
precip lifting across the cpv and our urban areas during the
peak evening commute, expecting areas of difficult travel.
Thinking ice accumulation up to a tenth or so is possible here
across the CPV and up to two tenths or so in the SLV and parts
of eastern/central VT. Temps with northwest winds continue to
struggle in the mid 20s, but all guidance suggests as warm
front lifts north winds will shift to the south and temps will
warm into the mid 30s by midnight in most locations. Have
adjusted pops/temps and precip type accordingly. Expecting band
of light to moderate precip to be along the international border
area by midnight with just spotty rain and pockets of freezing
rain as upper level dynamics and better moisture is either north
or west of our cwa. Better moisture and lift arrives with
surface cold front on Tuesday for another 2 to 4 hour window of
mainly moderate rainfall.

Previous discussion below:
Only minor changes to our current forecast through the evening
and overnight hours as low pressure near KDSM tracks toward Lake
Huron by sunrise Tuesday. We`re still looking at a period of
mixed precipitation along it`s accompanying warm front this
evening with light snow and ice accumulations expected. Latest
trends in the models have been to reduce the overall icing
threat across the southern and eastern portions of the forecast
area and showing more in the way of sleet. Quite a bit of
uncertainty exists in the exact thermal profiles however and
this leads to a low confidence forecast on eventual accretions
in these areas. As a result all Winter Weather Advisories remain
in place with this package. The warm frontal precipitation
should be rather brief (3-6 hours) so the ice amounts should be
generally on the light side, ranging from a few hundredths to
perhaps a quarter inch in the far northern SLV near KMSS. Some
snow and sleet will also be prevalent in the first few hours of
precipitation onset, especially across northern and eastern VT,
though again accumulations should be light and mainly from a
dusting to perhaps 2 inches. As the warm front pushes northward,
the low to mid level flow trends south/southeasterly by mid to
late evening in all areas save the far northern SLV. This will
foster steadily rising temperatures into the overnight hours and
morning hours on Tuesday as we firmly enter a pronounced warm
sector. During this time frame p-type should transition to
mostly spotty areas of light rain or showers with many areas
seeing a period of dry weather.

By Tuesday the system`s cold front marches steadily east through
time, crossing through northern NY in the mid to late morning, and
across VT during the afternoon. A period of steadier rainfall will
occur for several hours ahead of this boundary as temperatures climb
into the upper 30s to mid 40s for most spots. Contemplated adding an
outside shot of thunder as a narrow pre-frontal band of steeper mid-
level lapse rates and slightly negative Showalter values crosses the
area. Confidence is low enough however to preclude mention at this
point.

Behind the front temperatures steadily fall Tuesday night as
lingering precipitation transitions to light snows/snow showers and
takes on a more orographic character with synoptic flow trending
northwesterly. Some light backside accumulations of a dusting to 2
inches will be possible in these areas with some spot totals
slightly higher at the higher summits. Lows by Wednesday morning to
generally bottom out in the 15 to 25 range - coolest north and
west.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 351 PM EST Monday...After the cold front pushes through
Tuesday night, temperatures will fall throughout the day
Wednesday. Expect some residual snow showers lingering through
the day Wednesday. Additional accumulations during the day will
be restricted to under an inch in the northern Greens, with
other areas only seeing a dusting if anything. Behind the
frontal passage, the lower atmosphere will become better mixed
and winds could become gusty at times. The combination of the
colder air mass and the gusty winds will make for cold wind
chills Wednesday lasting through Thursday night. Wednesday
night, a surface high will build in from the northwest. This
will allow cloud cover to decrease and overnight temperatures to
bottom out in the single digits above to single digits below
zero. Thursday through Thursday night will be the coldest day of
the week (highs generally in the teens and lows near or below
zero) before warm air advection commences Friday.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 351 PM EST Monday...The temperature swings will continue
through the longterm with a warming trend starting Friday and
precipitation returning over the weekend.  After the system moves
through, expect early next week to be drier with temperatures
returning down to seasonal norms of 20s to low 30s by Monday.

Details...As the surface high shifts off the Atlantic Coast by
Friday evening, southerly return flow along the Eastern Seaboard
will transport warmer air northward. Meanwhile further west, a
surface low will form in the lee of the Canadian Rockies
Thursday night. Between the surface high to our east and the
strengthening lee low to the west, a southwesterly jet will
transport Gulf moisture northeastward. There is still some
question as to the extent of the amplification of the longwave
trough associated with this system, and the resulting extent of
the moisture transport/warm air advection ahead of the trough.
This is leading to greater uncertainty with the temperatures,
precipitation amounts, precipitation type, and precise timing
through the weekend. The trend of the 00Z ECMWF and the 06Z and
12Z operational runs of the GFS is towards a lesser amplified
trough and more progressive system, resulting in less moisture
transport into the North Country. However, a look at the GFS
ensembles reveals substantial spread among different ensemble
members with regards to the amplification of the upper-level
flow and the subsequent low-level baroclinicity associated with
the amplification of the flow. For this reason, not ready to
bite off completely yet on the deterministic trend towards a
slightly colder, drier system. With complex thermal profiles,
current thinking is we`ll see a fairly quick shot of mainly
rain sometime Saturday night through Sunday with the
possibility of some mixed precipitation on the front end and
back end of the system. If the warmer solutions do verify, the
system could provide some renewed hydro concerns. Will continue
to monitor trends in numerical guidance closely as models begin
converge on a better consensus for this storm.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
Through 00Z Wednesday...Widespread mvfr cigs and vis prevailing
across our taf sites this evening, with localized icing having
major impacts on the aviation community. Expecting conditions to
slowly improve at slk/rut/btv and pbg as temperatures warm above
freezing and steadier precip lifts north of terminals.
However...northeast winds and surface temps below 0c...will
result in additional icing at mss overnight and pockets of icing
at mpv. Thinking with developing southeast flow...areas of ifr
cigs are likely at mpv...while cigs lift to mvfr/vfr across the
CPV. Localized wind gusts btwn 25 and 30 knots possible this
evening at rutland from the southeast...with areas of moderate
low level wind shear and turbulence possible at all sites. A
band of moderate rain with additional mvfr and period of ifr vis
possible on Tuesday.

Outlook...

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

&&

.HYDROLOGY...
As of 320 PM EST Monday...Widespread rainfall is expected
across the area late tonight and especially on Tuesday. Current
data suggests 24 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 36 hours and
will be updated if later information suggests a different
scenario than current thinking.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory until 7 AM EST Tuesday for VTZ001-002-
     005-009-011-016-017.
     Winter Weather Advisory until 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-
     030-031-034-035-087.

&&

$$
SYNOPSIS...JMG
NEAR TERM...JMG/Neiles/Taber
SHORT TERM...RSD
LONG TERM...RSD
AVIATION...Taber
HYDROLOGY...JMG/Evenson



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