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  Sunday January 20, 2019

 

NWS Area Forecast Discussion


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FXUS61 KBTV 201757
AFDBTV

AREA FORECAST DISCUSSION
National Weather Service Burlington VT
1257 PM EST Sun Jan 20 2019

.SYNOPSIS...
Winter storm conditions will continue across the North Country today
with periods of heavy snow and blowing snow, especially this morning
where 1 to 2 inch per hour snowfall rates are likely, making for
hazardous travel. As low pressure departs to our east tonight,
frigid temperatures and very low wind chills are expected to develop
and continue through Monday night. Temperatures will moderate back
into the teens on Tuesday, and into the low to mid 30s Wednesday
when another storm system will bring another round of snow showers
with some rain possible in the deeper valleys.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 856 AM EST Sunday...Impressive UVV and snowfall rates
next 2-4 hrs, as combination of synoptic lift, strong 850mb
frontogenesis and strong moisture advection produce widespread
1.5-2"/hr snowfall rates. Seeing an increase in 35-40 dBZ echoes
in the Champlain Valley since 13Z (amazing with -1F to -2F at
the surface), and vsby is only 1/8SM at BTV. Temperatures remain
below zero, so conditions are dangerous (wind chills 10 to 20
below) and travel is generally not advised thru early afternoon
when snowfall rates start to taper off. Have increased snowfall
amounts 1-2" most sections with this update, with widespread
10-18" storm totals expected, and generally 8-12" in the St.
Lawrence Valley. SLRs remain near 10:1. The mix with sleet is
also on track for Rutland/Windsor counties, and should mainly
occur between now and 18Z. Please see our Local Storm Reports
and Public Information Statements for observed snow totals
across the region as we receive them.

Previous Discussion...Winter storm warnings continue across the
North Country today as surface low pressure over the central
Appalachians this morning tracks to the tip of Cape Cod by later
this afternoon and then off into the Gulf of St. Lawrence
tonight. Little overall change was made to the forecast this
morning but there are a few challenging parts to talk about.
First and foremost is snow ratios and temps. Models continue to
struggle mightily with low level cold air advection persisting
down the Champlain and St. Lawrence Valleys where temperatures
as of 4AM are still in the single digit below zero. Elsewhere
across the central Adirondacks and central/southern Vermont
where the 925mb flow has shifted southeasterly, temps have risen
into the single digits and teens above zero. A handful of
reports upstream indicate where southeasterly flow is more
prevalent, snow ratios have been ranged from 10-20:1, while here
at BTV where temps are much colder we`ve seen mostly needles
falling with very low ratios in the 8-12:1 range. Ratios have
increased recently across the Champlain Valley as a mesoscale
band associated with an enhanced ribbon of 700mb fgen is lifting
through, but expect after it passes we`ll be back into lower
ratios again until later this morning when better 850mb fgen
will pivot through the area. All told, I`ve lowered our snow
totals a couple inches from the previous forecast based on the
lower snow ratios, but we`re still highlighting a general 10-15"
from the Adirondacks westward through Vermont, with lower
totals of 7-9" across the St. Lawrence Valley through this
afternoon.

Snow tapers off later this afternoon and for this evening through
Monday the focus shifts towards rapidly falling temperatures and
areas of blowing snow as low pressure exits eastward and arctic high
pressure begins to build in from the west. Strong pressure gradient
between these features will support winds gusting 25-35 mph and when
combined with temperatures falling well below zero, dangerously cold
wind chills of -25F to -40F are likely. We`ve hoisting a wind chill
warning for tonight through Monday mid-day, with some additional
snowfall likely across northern areas as the parent upper level low
shifts over the region and some enhanced 700mb moisture rotates in
from the north. Could see an additional 2-4", and perhaps 6" at the
higher elevations late tonight through Monday.

&&

.SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
As of 307 AM EST Sunday...Dangerously cold wind chill continue
Monday night with values between -20 to -40 below, with coldest
values across the northern Dacks into the central and northern
Greens.

Deep closed mid/upper level circulation and associated sfc low pres
will be lifting across eastern Canada while 1039mb high pres builds
into our cwa. This continues to support brisk northwest winds thru
06z at 10 to 15 knots with localized gusts. However, expect winds to
slowly weaken toward sunrise, as high pres builds into the cwa,
especially over northern NY and temps will fall quickly btwn 09z-
12z. Expecting lows btwn -5f and -25f with coldest values over the
northern dacks/parts of the SLV. Any lingering snow shower activity
will quickly end over the northern Greens by 03z, soundings show
limited moisture.

By Tuesday, low level waa develops as winds shift to the southwest
and sfc high pres moves into eastern New England. Tues will be dry
with temps warming back into the teens. The warming trend continues
overnight Tuesday Night with strong low level waa on breezy 850mb
winds of 30 to 40 knots. Progged 925mb temps warm btwn -4c and -10c
by 12z Weds with increasing clouds and snow showers developing by
sunrise. NEK will see temps fall quickly in the evening, before all
areas warm into the mid teens to mid 20s with likely pops entering
the slv by 12z Weds.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
As of 307 AM EST Sunday...The combination of waa lift/moisture will
produce a period of mainly snow showers on Weds morning.
Initially thermal profiles support all snow with 925mb to 850mb
temps <0c thru 18z, before 925mb temps warm above 0c across the
slv/western dacks. Thinking as temps warm enough to support a
mix, best lift/moisture will be exiting our cwa, with just some
lingering light rain/snow showers possible. In addition, gusty
850mb southwest winds of 40 to 50 knots will create some
shadowing across the cpv on Weds, which will limit qpf/snowfall.
A general 1 to 3 inches likely with localized 4 inch amounts
for high peaks and northern Greens. Temps warming mainly 20s
east of the greens to mid 30s.

Uncertainty develops associated with potential wave along the
boundary on Weds Night into Thurs. In addition, plenty of
uncertainty with regards to low level thermal profiles and
associated ptype. Have kept things simple for now with high chc/low
likely pops and rain or snow showers. System sweeps off the east
coast overnight Thursday with much cooler air arriving for Friday
into the weekend. Some lingering mountain snow showers are possible
with temps falling back to below normal values.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
Through 18Z Monday...IFR/LIFR conditions will continue through
much of the period as a winter storm affects the area with
widespread moderate to locally heavy snow. The heaviest snow
with visibility 1/2sm or less will affect the terminals through
about 20z this afternoon, but overall anticipate snow to wane in
intensity through the evening hours as the storm pulls away.
However, winds have intensified in most spots and gusts to
22kt will be possible the remainder of the period. These winds
will keep visibility in the IFR category due to BLSN at most
terminals. Ceilings AOB 1500 ft will continue through the
period, though KRUT may pop up to 2500 ft after 02z tonight.


The heaviest snow
with vsby 1/2SM or less will affect terminals in the through
about 16Z with some sleet possibly mixing in at KRUT. Snow
lightens in intensity beyond 16-18Z as storm starts to pull away
but northerly winds gusting >20kts will keep vsby IFR or below
at many sites in BLSN through the remainder of the period.
Exception on winds will be KRUT where east-southeasterlies will
continue.

Outlook...

Monday Night: VFR. NO SIG WX.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. Chance SHSN.
Wednesday: Mainly VFR, with areas MVFR and IFR possible. Definite
SHSN, Likely SHRA.
Wednesday Night: MVFR/IFR conditions possible. Likely SHSN,
Likely SHRA.
Thursday:  Chance SHSN, Likely SHRA.
Thursday Night:  Chance SHSN.
Friday:  Chance SHSN.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...Winter Storm Warning until 4 PM EST this afternoon for
     VTZ001>012-016>019.
     Wind Chill Warning from 6 PM this evening to 1 PM EST Monday
     for VTZ001>012-016>019.
NY...Winter Storm Warning until 4 PM EST this afternoon for
     NYZ026>031-034-035-087.
     Wind Chill Warning from 6 PM this evening to 1 PM EST Monday
     for NYZ026>031-034-035-087.

&&

$$
SYNOPSIS...Lahiff
NEAR TERM...Banacos/Lahiff
SHORT TERM...Taber
LONG TERM...Taber
AVIATION...Hastings



 
 
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