Area Forecast Discussion
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FXUS61 KBTV 252018
Area Forecast Discussion
National Weather Service Burlington VT
318 PM EST Sat Feb 25 2017
A strong cold front will continue move eastward across the
North Country this afternoon and early evening. The leading edge
of the front will have strong gusty winds and heavy rain. Rain
will continue behind the front continuing the potential for ice
jams and river flooding through the weekend. Tonight, lingering
snow showers concentrated over the higher terrain will taper off
Sunday morning. More seasonable weather returns Sunday with
some light snow in the higher elevations before a quieter period
of weather to start the work week.
.NEAR TERM /THROUGH SUNDAY/...
As of 318 PM EST Saturday...Strong cold front moving through
Northern New York this afternoon has produced strong gusty
winds, heavy rain and isolated lightning/thunder. Gusty winds
out ahead of the front from strong 850mb jet...CXX VWP showing
50kts at 850mb has also helped with deeper mixing and strong
WAA, resulting in temperatures in the 60s to around 70. Expect
the leading edge of to reach the Champlain Valley around 22Z,
continuing east into central VT around 00Z and eastern VT
shortly thereafter. The very warm temperatures and the heavy
rain that is moving eastward across the area will continue the
flood threat. Already have some areas/rivers flooding (see
FLW`s) and expect the rain this afternoon and evening to result
in runoff reaching the rivers and rivers cresting on Sunday.
Observed 6-hourly rainfall amounts have generally ranged from
quarter inch to half inch. Rain will continue with still some
embedded areas of moderate to heavy rain possible into this
evening. Expect the back edge to move out of the SLV around 03Z,
CPV after midnight/05z. Lingering precipitation focused around
the higher terrain is expected through Sunday morning. Also
behind the front, the cold air advection surges in and we will
see 25-35 degree diurnal swings with lows in the mid-upper 20s
expected. Thus the precip lingering behind the anafront will
likely end as end as a period of rain/snow in the valleys and
heavy wet snow in the higher elevations where several inches of
accumulation are possible.
Sunday, some gusty winds of 30kts or less are possible in
lingering PGF before subsiding in the afternoon. Drier air will
move in with slight ridging at the surface. Max temperatures in
decreasing cloud cover will generally be in the 30s.
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 318 PM EST Saturday...Ridging at the surface continues
Sunday night, but a mid level shortwave will near the
international border Monday morning. Models disagree how far
south the shortwave will reach, but with limited moisture
available, have kept only slight chance POPs throughout the
period, mainly for higher terrain near the international border.
With increased cloud cover possible from the shortwave and
generally moderating temperatures as low level flow becomes for
SW, expect min temperatures Sunday night to be in the 20s.
Increasing 500mb heights indicative of continued moderating
temperatures in SW flow on the NW edge of surface ridge will
have Monday and Monday night dry with max temperatures in the
40s and mins in the 20s.
.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 318 PM EST Saturday...Tuesday the area will remain under
slight ridging aloft, but moisture and weak vorticity attempt to
move in from the south. NAM and GFS in agreement bringing
precipitation into at least the southern half of the forecast
area Tuesday afternoon, while ECMWF wait for developing low to
bring precipitation Tuesday night-Wednesday. This system
associated with deepening 500mb trough over the northern plains
states. Details of track of developing surface low and strength
continue to be under debate. Overall 12Z GFS and ECMWF show the
surface low to track near the international border, which could
start precip as rain through most of Thursday before the
associated cold front moves through. Lingering snow showers
possible late Thursday. Overall still time for models to focus
around a solution.
.AVIATION /20Z Saturday THROUGH Thursday/...
Through 18Z Sunday...Active weather is descending on the area
this afternoon with a line of showers and isolated thunderstorms
moving from west to east across the area between 18z and 02z.
During this time expect MVFR/IFR conditions for both ceilings
and visibilities due to the showers and isolated storms. Gusty
south winds...in the 20 to 30 knot range...will exist in advance
of the precipitation...then shift to the southwest and west
after 02z through the remainder of the period. Winds will taper
down a bit...but still be gusting in the 15 to 25 knot range. As
precipitation ends after 02z...visibilities will improve into
the VFR category and in the MVFR/VFR categories for ceilings.
Outlook 18Z Sunday through Wednesday...
18Z Sunday - 12Z Tuesday...Mainly VFR under high pressure.
12Z Tuesday - 00Z Thursday...VFR with chance MVFR/IFR rain
As of 430 AM EST Saturday...The flood watch remains in place
and is effective through Sunday evening. The record setting
warmth from Thursday through Saturday has already melted out a
significant portion of our snowpack with more warm air this
afternoon. The snow melt will combine with periods of heavy
rainfall associate with a cold front and produce significant
rises on nearly all rivers and streams across the region. And
the ground is also frozen, so not much will soak in.
Complicating matters is that some rivers, especially across
northern/northeast VT and in the Adirondacks are still ice
covered. Thus as the water levels rise and the ice weakens,
we`ll start to see ice movement. Which could very well then get
stuck in bends in the river or along bridges or where the rivers
go from a steeper to more gentle slope. By their nature, ice
jams are impossible to predict but can result in localized
flooding occurring quickly. In general, it takes the river to
rise 1.5 to 3 times the thickness of the ice to start the
breakup process. Based upon NERFC forecasts as well as ensemble
river simulations we continue to look at the Winooski @ Essex
Jct, and the Mad River @ Moretown for the primary focus of more
significant river flooding. Best river response will be late
Saturday through Saturday night due to runoff from snowmelt and
expected rainfall. Thickest river ice is in place across nern NY
basins and nrn VT, including the Chazy, Ausable, Winooski,
Lamoille, Missisquoi, and Passumpsic. Uncertainty in the river
forecasts are due to unknown exactly how much snow melt we are
getting and how much rainfall we will see on Saturday. Those
uncertainties are pretty large, so forecast changes are possible
as we move closer to the main event on Saturday.
Several more record high temperatures are expected to be broken
tomorrow on February 25, 2017. Here are the current records for
our long standing sites:
Burlington, VT 55|1985
Montpelier, VT 59|1985
St. Johnsbury, VT 60|2016
Massena, NY 50|1956
Mount Mansfield, VT 49|1961
VT...Flood Watch through Sunday evening for VTZ001>012-016>019.
NY...Flood Watch through Sunday evening for NYZ026>031-034-035-087.