Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 242332
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
732 PM EDT Tue Apr 24 2018

.SYNOPSIS...
High pressure will give way to low pressure tracking through
the region from Wednesday onward into the first part of the
upcoming weekend. Plenty of clouds along with a periodic threat
of showers or light rain are expected during this period as
temperatures trend cooler. Behind this system, confidence is
increasing for a substantial warm-up by the early to middle
portions of next week as high pressure returns to the northeast.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
As of 723 PM EDT Tuesday...Forecast is doing very well this
evening with mild temperatures and southerly winds at 5 to 15
knots. Updated to lower sfc dwpts 1 to 3 degrees and associated
rh values to match current trends, and bumped temps up slightly.
Otherwise...mid/upper level clouds will continue to overspread
the fa with rain showers arriving toward sunrise on Weds. Timing
of precip is tricky given very dry low levels and the potential
for initial surge to evaporate or fall as virga due to very dry
airmass. Current pops/qpf forecast looks reasonable with no
changes. Temps drop back into the 40s tonight and warm into the
50s on Weds with plenty of clouds/rain showers.

Previous discussion below:
Another outstanding day continues to unfold across the area as
departing high pressure, ample sun and modest southerly return
flow have boosted afternoon temperatures well into the 60s to
lower 70s. Humidity levels remain on the low side, but not as
extreme as we saw yesterday as southerly trajectories are
transporting a slightly higher dewpoints into the forecast area
on the back side of the surface high.

For tonight into Wednesday we continue to watch low pressure and
associated moisture lifting slowly northward from the Ohio
Valley/Mid Atlantic states. High clouds will slowly thicken and
lower over time with chances of showers increasing late across the
southern and western portions of the forecast area. Low temperatures
to run somewhat milder and more uniform as longwave radiative
processes become minimized later tonight - mainly 40s with a few 30s
in favored northern mountain hollows. Models remain consistent in
showing the aforementioned moisture phasing with a digging northern
stream upper trough approaching from the Great Lakes and southern
Canada tomorrow, and our current idea for increasing clouds and the
threat of light rainfall still looks good as we progress into the
daylight hours on Wednesday. The devil lies in the more discrete
details in regard to how "steady" this rainfall will eventually be
through the day with most recent hi-res guidance now suggesting a
more showery regime with orographic influences as the nose of a
modest southeasterly 30 kt jet lifts through the region. As such,
overall QPF was lowered slightly with p-type characterized as more
showery than a steady all-day rainfall. PoPs will remain high
however, so any outdoor recreational interests should be planned
accordingly. Given the abundance of clouds and light precipitation
around highs will trend cooler and range mainly through the 50s.

Showers then continue on and off for Wednesday night as the parent
upper trough tightens atop our area. Good PVA and moisture
convergence is associated with this feature, and combined with
relatively cool 700-500 mb thermal profiles high PoPs will be
maintained. There could be a few wet snowflakes mixed in at the
highest summit levels later at night but precipitation will be
largely characterized as light rain or showers. Given a near neutral
thermal advection regime in the lower levels minimum temperatures
should run quite similar to tonight - mainly upper 30s to mid 40s or
so.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
As of 321 PM EDT Tuesday...The surface low will exit to our northeast
Thursday, allowing for Wednesday`s precipitation to further
taper off into more orographically-focused showers throughout
the day Thursday. With the surface low departing towards the
Canadian Maritimes, the predominant flow over the forecast area
will be northwesterly/westerly. While wrap-around moisture will
be decreasing throughout the day as the low pulls away further
into eastern Canada, enough moisture will still be present
during the day to support an additional tenth to two tenths of
an inch of rain in favorable upslope areas of the western slopes
of the northern Adirondacks and Green Mountains. Other areas,
including the Champlain Valley, will be more prone to
downsloping and pick up lower accumulations on the back end of
the system Thursday.

Thursday night will be drier as shortwave ridging builds in.
Friday the forecast turns tricky as models struggle to come to a
consensus on the interaction of two shortwave features. The
longwave pattern will feature a broad trough digging over the
eastern half of the country, containing multiple pieces of
embedded energy with questionable interactions. A southern
stream cutoff low will lift out of the Southeast Friday just
ahead of a potent northern stream wave digging into the Great
Lakes Region. Initially, thinking was that the southern stream
low would go out to sea, leaving the North Country dry in
between features Friday. However, subsequent model runs
continue to trend slower with the northern wave, which would
open the door for the cutoff low to our south to lift into the
northeastern US and bring us some rain Friday. Both the 12Z
runs of the GFS and NAM are favoring this solution, while the
00Z ECMWF and 12Z GEM model runs continue to keep the North
Country drier Friday with the low tracking to our east. Current
thinking for this forecast package is that the track of the low
will lie somewhere in the middle of the two extremes, so
discounted the outlier 00Z ECMWF solution and favored more of a
12Z GFS/NAM/GEM blend in handling this system. The main changes
to the forecast that this supports is increasing our PoPs
Friday, particularly during the afternoon/evening hours, and
lowering our daytime temperatures slightly for Friday. Stay
tuned for future forecasts as uncertainty is fairly high during
this time frame.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 321 PM EDT Tuesday...The weekend will start off cooler and
showery on the back end of the departing system. After the
passage of a cold front, flow will become increasingly
northwesterly Saturday, advecting in cooler, drier air from
Canada. The good news is the coldest air will remain well to our
north, so the cool down behind the front won`t be anything
extreme. Surface temperatures will be generally in the 50s
Saturday, then fall into the 30s Saturday night as northwesterly
flow continues. Any lingering precipitation from the upper
trough will end Saturday night. Sunday will be drier, albeit
cooler, with highs in the 40s to low 50s.

After a slightly colder than average weekend, Monday will
feature a pattern shift that will usher in much warmer weather.
High pressure over the Ohio River Valley Sunday will shift to
the East Coast by Monday, putting our forecast area in
southwesterly return flow to start the work week. Both the
deterministic ECMWF and GFS are in agreement with keeping the
high pressure anchored off the southeastern US Coast through
midweek. A quick look at the GEFS ensembles also shows fairly
good support for anomalously high heights building over the
East Coast next week. For us here in the North Country, that
means sunshine and temperatures well above normal are looking
increasingly likely by midweek.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
Through 00z Thursday...VFR conditions will prevail through 12z
Weds with clouds lowering and rain showers arriving around 12z
Weds. Based on developing southeast upslope flow and northeast
flow at mss thinking mvfr cigs develop by midday weds...with
mainly vfr at pbg/btv/rut/slk, except developing mvfr cigs/vis
aft 18z with heavier precip band and lowering vis btwn 3-5sm.
Localized wind gusts to 25 to 30 knots possible at rutland from
the southeast by 18z. Some localized ifr is possible toward 00z
Thursday at mpv/mss with lowering cigs.

Outlook...

Wednesday Night: Mainly IFR, with areas MVFR possible. Likely
SHRA, Definite RA.
Thursday: Mainly MVFR, with local IFR possible. Chance SHRA.
Thursday Night: VFR. Slight chance SHRA.
Friday: Mainly VFR, with local MVFR possible. Chance SHRA.
Friday Night: Mainly MVFR, with local IFR possible. Chance SHRA.
Saturday: Mainly VFR, with local IFR possible. Chance SHRA.
Saturday Night: Mainly VFR, with local MVFR possible. Chance
SHRA, Chance SHSN.
Sunday: Mainly VFR, with areas MVFR possible. Slight chance SHRA.

&&

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

&&

$$
SYNOPSIS...JMG
NEAR TERM...JMG/Taber
SHORT TERM...RSD
LONG TERM...RSD
AVIATION...Taber



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