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vt discuss

Office: BTV

FXUS61 KBTV 202358

Area Forecast Discussion
National Weather Service Burlington VT
658 PM EST Tue Feb 20 2018

Record breaking warm temperatures expected overnight into Wednesday
which will cause significant snow melt and sharp rises on local
streams and rivers. Areas of ice jam and open river flooding is
possible overnight into Wednesday with scattered rain showers. A
cold front will quickly drop temperatures back into the 20s and 30s
by Wednesday night with drier conditions expected on Thursday.


As of 648 PM EST Tuesday...Forecast remains on track early this
evening. The main concern continues to be hydro and potential
for ice jam and open water flooding tonight into Weds from snow
melt caused by record warm temperatures. Only a few minor
adjustments for hourly temperature trends attm.

Water vapor shows 2 to 3 std above normal height ridge across the
eastern conus with pw values between 1.0 and 1.4, which is 4 to 5
std above normal. In addition, southwest 925mb to 850mb jet of 30 to
40 knots is helping advect very warm temps into our region with
925/850mb values btwn 9-14c. This has already produced temperatures
of 57f at Whiteface base and 50F atop Mt Mansfield, which has caused
some melting of snow pack, per web cams. Expect additional
significant snow melt overnight into Weds as temps remain steady at
mid/upper elevations in the upper 40s to mid/upper 50s. In the
valleys expect a wide range in temps overnight with l/m 50s
cpv/western dacks to upper 30s deeper valleys of central/eastern VT,
including the NEK.

Meanwhile...a sfc warm front is located near the international
border, which will serve as a focal for additional rain showers this
evening...before best 1000 to 500mb rh and 5h vorticity in the
southwest flow aloft pushes north of our cwa. Additional rainfall
amounts will be light and generally between 0.10 and 0.20 from MSS
to PBG to CDA. Highest pops will be across the northern tier...with
just schc over Rutland/Windsor Counties. The combination of very
warm temps and high sfc dwpts in the mid 40s to lower 50s advecting
over cold snow pack...expect areas of fog to develop, especially
eastern/central VT. Winds/mixing should limit fog development over
the cpv and parts of the SLV/dacks overnight.

Weds...very warm day expected as 925mb temps reach 13-14c across
central/southern VT by 18z Weds...supporting record breaking warm
temps of mid 60s to lower 70s. Elsewhere...the approaching sfc cold
front and associated ribbon of mid level moisture and sharp thermal
gradient highs start in the mid 50s to mid 60s...but drop back into
the upper 30s and mid 40s by evening over northern NY. NAM/GFS
continue to show ribbon of 850 to 500mb moisture...good sfc
convergence...and some 5h energy to help enhance a 1 to 3 hour
window of rain showers on Weds aftn. Additional qpf with boundary
will range from 0.05 to the heavier convective elements.
Temps drop 15 to 25 degrees in several hours behind the boundary on
Weds evening.


As of 351 PM EST Tuesday...Forecast area is under modest low level cold
air advection on brisk northwest winds of 10 to 20 knots. By
06z...925mb to 850mb temps range btwn -5c to -8c with lows
generally in the upper teens to mid 20s. The cwa will be between
building 1044mb high pres to the north and leftover
moisture/energy along the boundary across mid Atlantic/SNE. Have
continued to mention schc/chc pops south for Thurs Morning with
thermal profiles supporting a mix of rain/snow. Any qpf/snow
would be best moisture/dynamics still to our south
closer to the boundary. Highs near normal for Thursday with mid
20s to mid 30s.


As of 437 PM EST Tuesday...A deep subtropical high over Florida
will continue to push warmer air northwards and lead to
seasonably warm temperatures through the weekend. Expect highs
in the upper 30s to 40s with lows overnight in the low 30s. We
will still be in a fast flow regime with a shortwave moving in
late Friday and a stronger system moving in late over the
weekend. Both systems will follow a similar track up over the
Great Lakes going west and north of the North Country. This
means we'll be in the warm sector with rain and higher winds.
The winds should be stronger on Sunday as we see some
downsloping developing. Anticipate 20-25kts with gusts of
25-35kts along the western slopes of the Greens and the northern
slopes of the Adirondacks. Based on trends in guidance it does
appear that pattern change heading into next week but that
remains to be seen how it plays out for the North Country.


Through 00Z Thursday...Warm frontal zone remains draped from
west to east near the international border, and will continue to
result in HIR TRRN OBSCD and a range of ceiling and vsby
conditions at the TAF sites. Most of the rainfall will lift
north and west of the region, but periods of light rain are
possible overnight, especially for SLK/MSS. Through much of
tonight, will see conditions varying between MVFR and VFR at
PBG/BTV/RUT, mainly due to ceilings between 2.5-3.5kft. Ceilings
are lower elsewhere, with periods of LIFR expected. Will also
see some BR/FG at SLK/MSS, with vsby occasionally below 1SM.
Can't rule out some periods of fog elsewhere due to dewpoints
near 50F over rapidly melting snow overnight.

Winds overnight generally S-SW 5-10kts, except locally light NE
at MSS. Strong SW flow continues aloft, and will lead to all
stations except BTV seeing periods of LLWS overnight and thru
Wednesday morning. Generally looking at 2000ft AGL winds
30-40kts overnight. Frontal passage eventually brings a final
round of showers and a nwly wind shift between 19-22Z tomorrow.


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


As of 245 AM EST Tuesday...A 42-hour period of anomalously warm
temperatures will affect the region through Wednesday
afternoon. Periods of rainfall, modest winds and dewpoint
temperatures climbing into the 40s to lower 50s will foster
rapid snowmelt and ice break-up across the entire area. Also
boosting confidence are extremely high thawing degree hour
totals - averaging 900 to 1200 over the period. The model
consensus shows rainfall totals averaging from 0.5 to 1.50
inches across far northern VT into the northern Adirondacks and
St Lawrence Valley with the highest totals in the latter
location. Lesser amounts generally under a half an inch are
expected across central and southern VT. Taking this all into
account, modest to substantial river rises look highly probable
starting this afternoon and continuing into Wednesday, supported
by NAEFS/SREF MMEFS hydrograph data. While widespread open
water flooding is not expected, several rivers may approach
minor flood including the Ausable R. at Au Sable Forks, NY,
Missisquoi R. at North Troy, VT and the Winooski R. at Essex
Junction, VT. More importantly, numerous ice jams remain in
place from the substantial thaw this past January so the
potential for localized high water and/or flooding near these
features remain a real threat as ice break- up occurs.


Here are the current record high temperatures for February 20th
and 21st:

Record High Temperatures:

     ............Feb 20th....Feb 21st....
BTV.............58 (1981)...59 (1981)...
MPV.............56 (1994)...57 (1953)...
MSS.............63 (1994)...62 (1953)...
St. Johnsbury...60 (1981)...62 (1981)...

Record High-Minimum Temperatures:

     ............Feb 20th....Feb 21st....
BTV.............50 (1981)...49 (1981)...
MPV.............47 (1981)...47 (1981)...
MSS.............47 (1994)...41 (1981)...
St. Johnsbury...40 (1981)...46 (1981)...


VT...Flood Watch through Wednesday evening for VTZ001>012-016>019.
NY...Flood Watch through Wednesday evening for NYZ026>031-034-035-


NEAR TERM...Banacos/Taber