NWS Burlington, VT wrote its last area forecast discussion before the first event at Mar 9, 7:08 PM EST, 52 minutes earlier.
Area forecast discussion, Mar 9, 7:08 PM EST, 52 minutes before
Area Forecast Discussion
National Weather Service Burlington VT
708 PM EST Sat Mar 9 2024
.SYNOPSIS...
A powerful late winter storm will impact the North Country with a
wide varied of weather, from heavy wet mountain snowfall to a mix of
rain and snow in the valleys and breezy wind along the Western
Slopes. Given the heavy wet snowfall, scattered to numerous power
outages are possible, especially in the mountain towns above 1000
feet. A prolonged upslope accumulating snowfall is likely late
Sunday through Monday with significant additional snowfall expected.
Temperatures fall to near normal values for Sunday and Monday.
&&
.NEAR TERM /THROUGH SUNDAY/...
As of 640 PM EST Saturday...Main adjustment concerned tapering
winds gusts down a little with precipitation loading tamping
speeds by 5-10mph for most spots. Still, gusts 30-40 mph
possible through midnight for portions of the Highway 11
corridor across far northern New York. Winds shifting more
southeasterly overnight will favor stronger gusts along the
west slope of the Greens as the lljet moves across the North
Country. We're still on tap to see some gusts 40-50 mph in
Rutland and eastern Addison counties. Snow is ongoing above
1000ft elevation with rain/rain-snow mix elsewhere. The
forecast remains on track for a decent shot of mid-high
elevation snows with lower elevations accumulating tomorrow
evening/overnight into Monday.
Previous Discussion...All winter storm warnings and advisories
continue for our cwa, with very little change made to snowfall
and expected impacts.
Did issue wind advisory for central/southern Western Slopes from 00z
to 12z Sunday for localized gusts 45 to 50 mph.
Hydro continues to be watched very closely and is challenging to
determine amount of runoff with rain/snow event, but Otter Creek at
Center Rutland is now forecasted to reach minor flood stage on
Sunday aftn/evening and we are watching other lower elevation sites
like Winooski at Essex closely.
Greatest impact from this system wl be numerous power outages to
towns and cities above 1000 feet from the expected heavy wet
snowfall.
A large spread in the 10th and 90th percentile snowfall amounts
continues, indicating the challenge with this system, with
several sites increasing in the past 12 hours. We have continued
a conservative approach in our snowfall amounts toward the 25th
percentile, especially in the valleys.
Crnt radar and sfc obs indicate rain has overspread northern NY
this aftn, with snow occurring atop Whiteface and a temp of
27F. Without obs/webcams difficult to determine snow levels, but
feel they are pretty high and mostly above 2.5kft today. Winds
have been gusty from the south/southeast at 15 to 35 mph.
Have noted a slight shift in the RAP and latest HRRR/NAM 3km
guidance with track of sfc low pres, which pushes slightly
warmer air into VT and more potential for a mix of rain in the
midslope locations overnight.
Water vapor shows evolving full latitude mid/upper lvl trof with
elongated sfc low pres extending from the northern Great Lakes into
the southern Appalachian Mtns. As potent 500mb s/w energy
located over the MS Valley ejects northeast this evening,
primary low pres wl develop on leeside of the Appalachian mtns
tonight and track northeast toward SNE on Sunday. A strong sub-
tropical jet of 120 to 140 knots is helping with scale synoptic
ascent, along with advecting deep/rich moisture into our region,
as pw values surge btwn 0.75 and 0.90. This system wl have no
issue with available moisture, based on latest water vapor
trends, but initially lacks cold air making for an extremely
challenging and elevational dependent snowfall fcst.
The combination of dynamical and evaporational cooling wl help cool
the column just enough to support a heavy wet snowfall for towns and
cities above 1000 ft tonight. A strong elevational dependent
gradient is still anticipated from valley floors to mtn summits.
Soundings continue to show a large near isothermal layer near 0C
from sfc to 800mb for initial precip surge tonight, with strong
925mb to 850mb se flow helping to cool east side of the Greens just
enough, along with the eastern Dacks. Meanwhile, downslope warming
develops on western slopes, northern Dacks and parts of the NEK,
resulting in slightly warmer bl temps and a mix of rain/snow. I have
to admit its a been concerning to examine the 12z GFS output at MPV
and seeing 2.0" of qpf as heavy wet snow from 00z to 12z Sunday and
near 1.0" of qpf as snow for BTV. Given complexity of the system and
thermal profiles hovering near 0C, we are expecting some surprises
with this system in terms of areas under and overproducing on the
front end. Areas of greatest concerns are locally here in the CPV,
valley cities of central/eastern VT, including the NEK, and parts of
the northern SLV. As upper lvl dynamics and associated cool pocket
of air moves directly overhead btwn 09z-14z Sunday, expect a burst
of wet snow for most, including valley locations. Snowfall totals
have changed very little for first part, ranging from a dusting to
several inches in the valleys below 1000 feet to 6 to 12 inches
midslopes and summits. Temps hover either side of freezing
overnight. Total qpf for first part ranges from 0.50 to 1.25 with
localized higher amounts in the se favored upslope regions of the
central/southern Greens.
Have continued wind advisory for central/southern Western Slopes of
the Greens from 00z-12z Sunday. The core of strongest 925mb to 850mb
winds of 45 to 65 knots occurs btwn 03z and 09z, before axis shifts
to the east. Mixing is questionable as core of strongest winds are
colocated when precip is the heaviest, but examining sounding data
at RUT showed the potential for localized gusts 45 to 50 mph.
For Sunday, initial surge of deep layer moisture and associated fgen
forcing wl exit our northern cwa btwn 14z and 16z, with a decrease
in areal coverage of precip. Feel lingering snow showers wl be most
concentrated over the mtns on Sunday midday. With break in precip
and limited caa, temps should warm into the mid 30s to lower 40s,
with any slick travel quickly improving for a period of time. After
18z winds begin to shift to the northwest as deepening system
becomes vertically stacked to our east. Developing upslope flow and
associated caa and backside 700mb deformation zn wl enhance areal
coverage of precip again acrs most of the region. Initially bl temps
support all snow above 1500 feet, but as caa continues rain quickly
changes to all snow to the valley floors by 00z Monday. Additional
moderate to heavy snowfall is anticipated Sunday night into Monday,
with significant accumulation likely in the western slopes and
northern dacks.
&&
.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
As of 354 PM EST Saturday...Conditions look very favorable for a
prolonged and significant upslope event for the northern Dacks and
central/northern Greens during this time frame. A much drier and
fluffier snowfall is anticipated with additional snowfall amounts
varying greatly based on elevation. A dusting to 4 inches here in
the CPV to 6 to 12 inches likely Western Slopes, with localized
amounts from Mt Mansfield to Jay Peak of 12 to 18 inches possible.
Northern Dacks see similar type amounts of 6 to 10 inches with
localized amounts of 10 to 16 inches possible with 2 to 6 inches in
parts of the SLV. Much lighter in the lower CT River Valley
associated with downslope flow. Snow ratios wl quickly be changing
as thermal profiles cool and progged 850mb temps drop btwn -10C and
-14C by 03z Monday. Given deepening low pres near 985mb, expect
breezy to gusty northwest winds of 15 to 30 mph with gusts 30 to 45
mph possible acrs downslope areas of the mtns. Eventually vertically
stacked system slowly pulls away and upslope snow showers wl slowly
decrease in areal coverage on Monday night. Have pops/qpf and snow
amount grids to match this thinking. Temps are below normal on
Monday with northwest winds and precip.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 354 PM EST Saturday...Uneventful weather is expected Tuesday
through Thursday with a return to above normal temperatures and
possibly some rain showers as clouds tend to increase midweek. The
Friday - Saturday timeframe looks unsettled with a frontal boundary
likely in the vicinity with a weak wave or waves moving along it to
help produce mainly rain but possibly higher elevation snow
depending on the storm track.
Have PoPs in the likely category Friday night when best consensus
exists on a period of steady precipitation, but this pattern does
not lead to high confidence onset/cessation of rain and/or snow.
Also snow level uncertainty is large given that north of the frontal
boundary low level temperatures probably will be cold enough for
higher elevation snow. So while this precipitation event will likely
be rain for most locations as the latest forecast shows, the west-
east orientation of a thermal gradient will also mean wet snow could
fall if a wave passes to our south and would be more likely as one
goes northward for a given elevation.
The flow pattern looks rather zonal, especially compared to recent
storms, which will limit the potential precipitation amounts. The
latest NBM currently suggests a roughly 5 to 15% chance of exceeding
an inch of precipitation over this 48 hour period. That being said,
southwesterly low level flow looks moist enough such that NAEFS
water vapor transport and PWAT for that period is in the 90th
climatological percentile supporting heavy rain if other ingredients
line up. The 12Z global models do show a very low probability
scenario (9% of all ensemble members), driven mainly by the GEPS,
with a more amplified upper air pattern and chances of heavier
precipitation. It bears watching if this idea gains more support, as
it would change the forecast towards potentially heavier showers and
a more significant warm up that could lead to flooding given the
recent wet/snowy weather.
Overall, this period will be rather mild if not unusually so with
temperatures on Tuesday mainly in 35-45 range and mainly in the 45
to 55 range Wednesday through Friday, likely trending cooler over
the weekend especially if skies remain cloudy.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
Through 00Z Monday...Overall trends through the next several
hours will be from VFR/MVFR to widespread MVFR by 05Z and
eventually IFR at all sites by 10-12Z. Precip type will mainly
be snow, though locally rain or rain/snow at KBTV/KMSS. After
12Z, precip tapers off but IFR/MVFR ceilings will persist
through the remainder of the period. Winds will remain brisk at
the surface and aloft tonight with areas of LLWS and local gusts
of 20-30kts from the SE at KRUT. After 12Z winds drop off
significantly below 10kts, before ramping back up from the W
after 18Z to 10-20kts.
Outlook...
Sunday Night: Mainly MVFR and IFR, with local VFR possible.
Definite SHSN.
Monday: Mainly VFR, with areas MVFR possible. Windy with gusts to
30 kt. Chance SHSN.
Monday Night: Mainly VFR, with local MVFR possible. Chance SHSN.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.
Wednesday Night: Mainly MVFR, with local IFR possible. Slight
chance SHRA.
Thursday: Mainly VFR, with local IFR possible. NO SIG WX.
&&
.HYDROLOGY...
A widespread mix of rain and snow will develop across the HSA
tonight with liquid precipitation amounts of 0.50 to 1.25 inches
expected in the valleys. It is very difficult to determine rain/snow
and potential runoff, but given high river flows currently our best
river forecasts indicate the Otter Creek at Center Rutland could
reach minor flood stage late Sunday. In addition, the Winooski at
Essex may reach action stage, with several other rivers rising to
bankful. It should be noted, if a warmer solution verifies with more
rain, additional minor flooding is possible.
&&
.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Weather Advisory until 8 PM EDT Monday for VTZ001>005-
007-009-011-021.
Winter Storm Warning until 8 PM EDT Monday for VTZ006-008-010-
016>020.
Wind Advisory until 8 AM EDT Sunday for VTZ011-018-019.
NY...Winter Weather Advisory until 8 PM EDT Monday for NYZ026-028-
035-087.
Winter Storm Warning until 8 PM EDT Monday for NYZ027-029>031-
034.
&&
SYNOPSIS...Taber
NEAR TERM...Boyd/Taber
SHORT TERM...Taber
LONG TERM...Kutikoff
AVIATION...Lahiff
HYDROLOGY...