Area Forecast Discussion
Issued by NWS Burlington, VT

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000
FXUS61 KBTV 241508
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1008 AM EST Fri Nov 24 2017

.SYNOPSIS...
High pressure over the mid-Atlantic states this morning will briefly
build northward into the Northeast today allowing skies to clear and
temperatures to rise into the low to mid 40s on increasing southerly
flow. A low pressure system passing to our north on Saturday will
bring a trailing cold front across the North Country accompanied by
scattered rain and snow showers through Saturday night. Cloudy and
dry conditions are expected for Sunday.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 1002 AM EST Friday...A quiet end to the work week is
expected today as high pressure over the mid-Atlantic states
builds northward into the Northeast, gradually scouring out low
stratus deck across the region this morning. Have slowed the
clearing trend based on current satellite trends with the mid-
morning update. Also of note, are well-defined lee waves east of
the Adirondacks/Green Mtns in the stable layer near ridgetop
level. The wave clouds are most pronounced east of some of the
higher summits across the spine of the Green Mtns, and appear
even deeper east of the White Mtns in NH. In any event, outside
of a few scattered snow showers and/or flurries across northern
areas early this morning, it`ll be a dry, mild and increasingly
windy day as a strengthening pressure gradient between the high
and an approaching low to our west will develop southerly winds
of 10-20 mph, with a few gusts to 30 mph in vicinity of Lake
Champlain. Highs will touch 40 across the Adirondacks and
Northeast Kingdom, while warming into the mid-40s elsewhere.

Dry conditions continue through tonight as well as the North
Country will be entrenched in a warm sector with a warm front to
our north and a cold front to our west associated with low
pressure passing well north of the border. South winds will
remain brisk as the pressure gradient remains tight between the
departing high and approaching low. This will keep overnight
mins on the mild side in the mid/upper 30s across the deeper
valleys, while the mid-slopes of the Adirondacks and eastern
Vermont should drop off into the upper 20s to around 30.

Aforementioned cold front approaches Saturday but really
doesn`t swing through the forecast area until after sunset with
a little pre- frontal trough and associated deep layer moisture
producing some scattered showers through the day, mainly in the
form of rain but a few snow showers are possible across the
higher elevations during the morning hours. Overall QPF is very
light, generally less than a tenth of an inch, so expect little
to no snow accumulation and minor impacts to outdoor activities.
Temps remain mild through the day, warming a couple degrees
from Friday`s maxes in the low/mid 40s.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 326 AM EST Friday...00Z guidance all still indicating a
shortwave moving across the region Saturday night, but have
backed off a bit on its intensity. Still looking at a period
where scattered snow showers will increase in coverage,
especially across the higher terrain of northern NY and northern
Vermont. The primary tweak to the going forecast is to decrease
the PoPs a few hours quicker on Sunday. Could still have a few
high terrain snow showers Sunday morning, but think by noon
those will be all gone. Still only expect minor accumulations,
perhaps 1-2" at the higher elevations, and a dusting at low
elevations. Once the snow showers across the north diminish, it
will be a dry but rather cloudy afternoon with northwest winds
occasionally gusting to 20 mph. Highs will be slightly below
normal, generally low-mid 30s.

Sunday night we should see another round of scattered snow showers
or periods of light snow across the region as a weak Alberta Clipper
and it`s associated upper level trough zips by just to our north.
This system will also not have a lot of moisture to work with,
basically what it can tap from the Great Lakes. So it looks like
another situation where we have 1-2" at higher elevations, with a
dusting at lower elevations.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 326 AM EST Friday...00Z guidance still pointing at a rather
progressive synoptic pattern next week. We`ll start off with a
brief shot of cooler northwest flow for Monday, but quickly
transition to a westerly flow pattern that turns more southwest
by mid/late week. So it looks like from Tuesday onward,
temperatures will be above normal. 00Z GFS and ECMWF are in
decent agreement with the overall pattern. The main "weather"
features will be a weak front late Tuesday/early Wednesday, and
then the next low pressure approaching late Thursday. A few
notes on each day follow...

Monday: Looks to be the coldest day of the week. Perhaps a few
morning mountain snow showers, but some prospects for some sun by
afternoon.  925mb temperatures drop to -8 to -10C, so expecting
highs only in the upper 20s to lower 30s, with mid 30s in southern
valley locations.

Tuesday:  Looks dry. Flow turns southwest ahead of an approaching
front, with warmer air advecting in. 925mb temperatures should warm
to about +5C by late in the day. This will support temperatures well
into the 40s for most areas - perhaps a few places nearing 50F.
Reasonably tight pressure gradient will support 40-50kts of wind
around 850mb. So it will likely be a bit breezy (20-30 mph gusts)
especially in the St Lawrence and Champlain Valleys. Did try to
enhance the winds some in the gridded forecast as base model data
that far in the future typically underestimates wind speeds.
Weakening front comes through Tuesday night. Temperatures should be
warm enough aloft and in the boundary layer that we are looking at
light rain as the dominant precipitation type.

Wednesday: 00z guidance is a little faster with previous model runs
and suggests that it will be mostly dry for the day. However, given
uncertainty in timing, maintained some PoPs in the event the front
comes through during the morning. Temperature profiles would suggest
rain showers ending as a little bit of higher elevation snow
showers. Not a very robust front, so we aren`t talking about a lot
of rain or snow.  Also not a lot of cold air behind the front, so
temperatures will still be above normal with highs in the lower
40s.

Thursday: Uncertainty in the forecast increases as GFS and ECMWF
have more significant timing differences. Both indicate high
pressure moves off the coast with flow turning southwest ahead of
the next low pressure system. However GFS is faster with bringing in
moisture and precipitation by later in the day. ECMWF is about 12
hours slower. Do have some 15-25% PoPs in for Thursday and at
the very least increasing clouds. In any event, highs will again
be slightly above normal.

&&

.AVIATION /15Z FRIDAY THROUGH TUESDAY/...
Through 12Z Saturday...Widespread OVC VFR ceilings with a few
areas of MVFR will lift from south to north and scatter out to
FEW200/SKC this afternoon and remain VFR through the rest of
the period.

Winds will be mainly south/southeast at 6-10kts from KPBG
eastward with some gusts this afternoon and evening up to 20kts
at KBTV. Westward at KSLK and KMSS southwesterlies will prevail
at 08-12kts with gusts to 20kts and likely some LLWS and
turbulence after 23Z as a low level jet streaks in. Approaches
over Lake Champlain will also be quite bumpy this afternoon and
overnight with low level winds in excess of 30kts likely over
the open waters.

Outlook...

Saturday: Mainly VFR, with local MVFR possible. Scattered SHRA.
Saturday Night: Mainly MVFR, with areas VFR possible. Chance
SHRA, Slight chance SHSN.
Sunday: Mainly VFR, with local MVFR possible. Slight chance SHSN.
Sunday Night: Mainly MVFR, with local VFR possible. Chance SHSN.
Monday: Mainly MVFR, with areas VFR possible. Slight chance SHSN.
Monday Night: Mainly VFR, with local MVFR possible. NO SIG WX.
Tuesday: VFR. Slight chance SHRA.

&&

.MARINE...
As of 257 AM EST Friday...A LAKE WIND ADVISORY is in effect for
increasingly strong winds over the open waters of Lake
Champlain this afternoon through Saturday morning. South winds
of 10 to 20 knots over the lake this morning will increase
markedly this afternoon and especially overnight, where winds
will likely top 30 knots with some gusts to 40 knots possible.
This will produce very hazardous conditions with wave heights
building to peak heights of 5 to 7 feet for a period tonight.
Behind a cold front passage, winds will shift to the west and
decrease Saturday afternoon.

&&

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

&&

$$
SYNOPSIS...Lahiff
NEAR TERM...Banacos/Lahiff
SHORT TERM...Nash
LONG TERM...Nash
AVIATION...Lahiff
MARINE...Lahiff



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