Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/07/23

Area Forecast Discussion

National Weather Service Burlington VT

 925 PM EST Mon Nov 6 2023

.SYNOPSIS...
Winds increase through tonight with gusty conditions continuing into
Tuesday as a passing low pressure system brings unseasonably warm
temperatures and scattered to numerous rain showers. A passing cold
front Tuesday will bring colder and drier conditions through
Wednesday night with freezing temperatures expected. Then another
system will move northeastward Thursday bringing increasing concerns
for a mixed precipitation event that might impact the morning
commute for portions of the North Country. Another round of
unsettled and colder conditions possible for the weekend.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
* Gusty southerly winds develop tonight with potential to bring down
  a few tree limbs possibly causing some isolated power outages,
  especially for exposed locations adjacent to Lake Champlain and
  along portions of Highway 11 in northern New York.

As of 924 PM EST Monday...The forecast is in pretty good shape
so there were only a few updates. The main story tonight
continues to be the winds, especially north of the Adirondacks
and in the Champlain Valley, where gusts are currently
forecasted to peak around 35-40 mph later tonight. Gusts have
exceeded 30 mph in most of these areas but they will still
increase a little from there as the axis of strongest winds
moves through. No significant wind changes were made at this
update but they will be mentored closely tonight. The POPs
associated with the steadiest rain were lowered a little as it
does not seem as full as previous forecasted, but the timing
remains the same. Temperatures were adjusted slightly to match
obs but there were no major changes. Previous forecast
follows...

The much mentioned clipper style low will move through southern
Canada tonight and Thursday with two distinct surface waves
moving through the North Country. Models continue to prog a
strong LLjet associated with this system to move over the North
Country in between 7pm this evening and 7am Tuesday morning
nearly coincident with the first surface wave. With surface flow
southerly, there will be downsloping along the northern flanks
of the Adirondacks towards Highway 11 in northern New York;
strongest winds here will be in the general area of Malone, NY.
Meanwhile, flow will channel in the Champlain Valley across Lake
Champlain. These processes will help bump surface speeds with
gusts generally 30-40 mph in general with more intermittent peak
gusts around 45 mph. These speeds may bring down some weaker
limbs and potentially cause very isolated power outages.
Elsewhere, winds will be more dampened gusting 20-35 mph in
general. Winds will begin to shift Tuesday morning through the
afternoon becoming southwest then west as the second trough
pushes through the region. Downsloping to the east of the Greens
will peak Tuesday afternoon with gusts 30-40 mph possible.
Winds will taper down Tuesday evening, but remain breezy through
Tuesday night with moderately strong cold air advection
bringing temperatures below freezing for most spots outside of
Lake Champlain.

Precipitation-wise, this system will be largely limited by its
translational speed with general amounts ranging from around 0.1" or
less in areas shadowed by the downsloping winds to around 0.5" in
higher terrain. Northern New York will likely do better after the
first surface feature when winds shift more upslope with generally
amounts closer to 0.25". Strong warm aid advection will keep
freezing levels elevated above 3500ft with the peaks potentially
seeing some snow totaling less than 1". Winds will keep temperatures
from decoupling tonight as well as continue to advect warm air into
the North Country; lows in the 40s will likely occur towards
midnight with a non-diurnal trend of warming through the early
morning hours. Daytime temperatures Tuesday will likewise be well
above seasonal averages in the low/mid 50s for broader valleys and
around 50 degrees elsewhere. After the second trough passes,
temperatures will cool through the late afternoon and overnight
hours with lows in the 20s for most spots and lower 30s for the
Champlain Valley.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 328 PM EST Monday...Unseasonably cold weather is the main story
for Wednesday. A lobe of polar air that dropped southeastward
Tuesday night will settle into the region as high pressure follows
behind. The air mass can be characterized by 850 millibar
temperatures near 12 to 14 degrees below zero Celsius, roughly
typical of mid-winter. With this cold air mass aloft only slightly
moderating during the day, even good mixing will bring temperatures
only up into the mid and upper 30s for most spots during the
afternoon. Breezy northwest winds will produce wind chills in the
teens to low 20s during the morning with some improvement as the day
wears on.

The secondary weather story will be light precipitation. During the
morning, we will see some snow showers in northern Vermont diminish
with advection of drier air aloft. While not explicitly forecast,
favorable temperatures for snow growth could lead to flurries where
skies remain overcast through at least the first half of the day,
especially in favorable upslope locations. Then by late Wednesday
night, we will be focused on the next system, a warm front that will
be pushing northeastward bringing a wave of light widespread
precipitation. Given that a ridge of high pressure will still be
overhead Wednesday night and dry air mass, temperatures should fall
back below freezing in advance of the precipitation, setting the
stage for potentially impactful winter weather. Onset time is an
important forecast, and the best guess at this point is
unfortunately daybreak, generally spreading southwest to northeast
in the predawn hours. That means greatest chance of a wintry mix
overnight will be in our southern and western areas. Current PoPs at
4 AM show 33-50% chances roughly across Windsor, Rutland, and
Addison County in Vermont and most of northern New York save far
northern areas and northern Champlain Valley. Precipitation type
discussion will be below in the Long Term section.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 328 PM EST Monday...Thursday will feature a light wintry mix of
precipitation, with all precipitation types probable in the region
trending towards plain rain. Due to the initially very dry low level
air, wet bulb cooling will support onset as a burst of snow before
we see that wintry mix. Valley locations that see southerly surface
winds, such as up the Champlain Valley, may see only plain rain.
While there is important spread in how cold the air will be,
forecast soundings generally suggest snow will develop and then melt
fairly high up before refreezing near the surface. Depending on the
depth of the refreeze layer and magnitude of the warm layer, we
could see periods of both sleet and freezing rain. Regardless,
chances of frozen precipitation is high. With that idea,
precipitation types for most locations shows a progression from snow
or sleet to sleet and freezing rain, with our likely colder hollows
in central and eastern Vermont still seeing some frozen
precipitation with lingering sub-freezing air even late in the day.
A wild card is ground temperatures; many surfaces after the cold
Wednesday may become frozen, but expect many roads, especially in
lower elevations, could stay warm enough to reduce ice accumulation.

Some of the variations in precipitation type are tied to storm
track. Ensemble members have become a bit more clustered to the idea
of a track near the St. Lawrence Valley. With low pressure passing
to our west, we due tend to maintain a cooler easterly wind east of
the Green Mountains and hourly temperatures in many areas are shown
to stay near 32 through much of the day. Northeasterly winds in the
northern St. Lawrence Valley will also create locally higher chances
of ice accumulation if freezing rain lingers as the main
precipitation type. Overall, given the fast system movement and type
of forcing, precipitation amounts will not be heavy, likely in the
range of 0.1" to 0.33" of liquid.

The upper level flow pattern suggests that the surface wave and weak
low pressure system that brings the wintry mix will be absorbed in a
gyre centered to our northwest. As another wave pushes eastward, it
will down polar air with a sharp front on the leading edge located
across southern Canada on Friday. Expect some decent southerly flow
trending westerly in advance of the main frontal boundary which will
be driven southward by a strong upstream ridge. For now,
precipitation chances suggest isolated to scattered snow showers,
but we`ll have to watch if ingredients come together for more
intense and widespread snow showers. Given marginal surface
temperatures ahead of the boundary, there would be potential impacts
with any heavier snow showers. However, the air mass change doesn`t
look particularly large; even the 10th percentile of the global
ensemble 850 millibar temperature is warmer than what we will see on
Wednesday. Saturday will be blustery with perhaps another round of
flurries and a few snow showers, while Sunday likely will be the
colder and sunnier day of the weekend as strong high pressure builds
in. Overall, temperatures throughout the long term period will be on
the cool side during the day, mainly in the 30s and 40s. The
persistent breezes and cloud cover will keep temperatures at night
more typical of the season in the 20s to low 30s.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Through 00Z Wednesday...Primary aviation concern for this
period continues to be the LLWS and mechanical turbulence as a
strong LLjet transit the North Country. LLjet of 45-60kts will
move across the region west to east mainly 00-15Z with flow
aloft shifting southerly to southwesterly 00-12Z and
southwesterly to westerly 12-18Z. Strong ridge level winds will
oscillate with at least moderate mountain wave turbulence
expected. Southerly winds begin gusting after 22Z around 20-25kt
increasing 01-08Z as high as 35kt at southerly wind favored
terminals like BTV. SFC winds will taper down briefly after
08-12Z before the SFC flow turns southwesterly/westerly ahead of
the next trough(which will pass through 18-22Z Tuesday).

There is an Icing Airmet out for the region mainly above FL020
in cloud cover which could present a hazard for aircraft without
deicing equipment. Precipitation chances will increase after
02Z mainly in the form of rain at terminal surfaces with the
freezing remaining above 2500ft MSL through the period.
Otherwise, conditions will remain largely VFR until after 03-06Z
when surface winds begin shifting southwesterly. CIGS will sag
lower after 12Z, but SFC winds remain gusty out of the northwest
likely keeping IFR conditions at bay. Best chances for any IFR
CIGs will be at SLK/MPV after 12Z.


Outlook...

Tuesday Night: Mainly VFR, with areas MVFR possible. Slight
chance SHRA, Slight chance SHSN.
Wednesday: VFR. NO SIG WX.
Wednesday Night: VFR. Likely FZRA, Chance SN, Chance PL.
Thursday: Mainly MVFR and IFR, with areas VFR possible. Likely
PL, Chance RA, Likely FZRA, Likely SN.
Thursday Night: Mainly MVFR, with areas IFR possible. Slight
chance SHRA, Chance FZRA, Slight chance SHSN.
Friday: Mainly MVFR, with local IFR possible. Slight chance SHRA,
Slight chance SHSN.
Friday Night: MVFR/IFR conditions possible. Slight chance SHRA,
Slight chance SHSN.
Veterans Day: Mainly VFR, with areas MVFR possible. Slight chance
SHRA, Slight chance SHSN.

&&

.MARINE...
A Lake Wind Advisory is in effect this evening and tonight.
Gusty winds increase tonight with speeds ranging 30-45 mph.
This will create hazardous conditions for small watercraft on
Lake Champlain. Winds will begin to decrease late Tuesday
morning as southerly flow turns westerly, but will increase
again as a second trough moves through the region. Gusts 20-35
mph will be possible Tuesday afternoon.

&&

.BTV WATCHES/WARNINGS/ADVISORIES...
VT...None.
NY...None.

&&

$$
SYNOPSIS...Boyd
NEAR TERM...Boyd/Myskowski
SHORT TERM...Kutikoff
LONG TERM...Kutikoff
AVIATION...Boyd/Verasamy
MARINE...WFO BTV