Area Forecast Discussion
Issued by NWS Burlington, VT

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658
FXUS61 KBTV 250756
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
356 AM EDT Fri May 25 2018

.SYNOPSIS...
Summerlike weather arrives today as high pressure brings warm
temperatures to the area. A cold front will approach from the
north tonight, and linger across the region over the weekend. As
a result, expect an increase in cloud cover, cooler
temperatures and chance of showers and thunderstorms through the
period. A few of the storms could produce locally heavy
downpours.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 339 AM EDT Friday...Warm temperatures remain in the cards
for today as a westerly surge of continental air has arrived
overnight on the nose of robust 50+ kt mid-level jet (Whiteface
Summit winds of 50G59kt as of 330 am). High temperatures should
top out in the upper 70s to lower 80s area wide with perhaps a
few mid- 80s in favored downslope areas of the Champlain and CT
River Valleys. There will also be a broad increase in columnar
moisture by this afternoon with model- averaged PWAT values
increasing to near 1.5 inches by early evening. On the nose of
this higher moisture variable mid- level cloud cover should
advect across central and northern counties through the day and
especially by early evening. Only limited dynamical support for
lift exists however, so outside a very brief light shower or
sprinkle in these northern areas mainly dry weather is expected
through late afternoon. With the boundary layer deepening into
the 850-825 mb level this afternoon gusty winds also look like a
certainty with west to southwesterly peak gusts topping out in
the 20-30 mph range in the noon to 500 pm time frame.

By this evening a more concerted push of moisture and lower end mid
level instability advect into the region in advance of a backdoor
cold front dropping south/southwestward from southern Quebec. I`ve
largely ignored the swaths of excessive QPF offered by some of the
00Z hi-res NAM/WRF output given only marginal lifting mechanisms,
though weak bundles of shortwave energy traversing the area in the
west to northwesterly flow aloft should be sufficient to produce
scattered showers across the northern tier of counties accordingly.
An isolated storm also can`t be ruled out but coverage of storms
should be on the low side. Mainly dry weather continues across
southern counties. Low temperatures a bias-corrected consensus blend
of guidance with values generally ranging from the mid 50s to lower
60s in milder valley locales.

The start of an active weekend of weather then begins on Saturday as
a fairly sharp backdoor cold front is forced south/southwest into
the area by expansive high pressure bridging east across central
Quebec. Moisture pooling to the south of the boundary along with
CAPE values from 250-750 J/Kg should be sufficient to generate
numerous showers and a band of embedded thunderstorms by afternoon.
Some variability exists within this morning`s models on the exact
zone of convective development, though a consensus solution would
suggest areas from the Adirondacks east through central and southern
VT have the highest probabilities where brief heavier downpours will
be possible. The thunder threat across the northern tier isn`t non-
zero either, but our current forecast of a morning frontal passage
suggests an earlier arrival of a cooler, more stable airmass under
increasingly cloudy skies. Maximum temperatures will also support
this timing with another day of upper 70s/lower 80s across the
south, and upper 60s to lower 70s across the northern tier.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 347 AM EDT Friday...In the evening hours the backdoor
cold front will continue to sag slowly south across the North
Country on Saturday. The front sort of washes out as the flow
across Vermont and the western Champlain valley turns west to
southwest as a modified marine airmass moves in from the south
and east. 925mb temps cool in this region with increasing
humidity, however across the Saint Lawrence southerly flow
continues and a much warmer airmass will hold in place. That
will lead to lows Saturday night east of the Adirondacks in the
low to mid 50s with near 60 for low temps in the Saint Lawrence
Valley.

The modified marine air mass will lead to stabilization of the
boundary layer heading into Sunday under mostly cloudy skies.
With the stable boundary layer we should be mostly precip free
across the Champlain Valley and the rest of Vermont. Its a
different story across the Saint Lawrence valley where we`ll
see partly cloudy skies with a rapidly destabilizing atmosphere.
Temps should warm into the low 80s with dew points in the upper
50s to low 60s. MUCAPE in the Saint Lawrence Valley increases
into the 1000-1500 J/kg by mid afternoon. An upper level trough
will swing a shortwave through the Saint Lawrence and that
shortwave will be the needed forcing for storms to develop.
Combine the shortwave with a PWAT surge and these ingredients
will lead to the potential for thunderstorm development with
possibly heavy rainfall in the afternoon. CAM models continue to
depict bullseyes of 1-2"/hr rates in the region and so we`ll
need to monitor any storms closely.

The upper level through finally swings through the North
Country on Monday and will lead to some additional scattered
shower activity on Monday with dry weather returning behind a
frontal system Monday night.

&&

.LONG TERM /TUESDAY THROUGH THURSDAY/...
As of 347 AM EDT Friday...A ridge of high pressure builds in
behind the system on Monday and leads to moderating temperatures.
Tuesday should be a pleasant day with semi breezy conditions
and temps warming into the mid 70s. We`ll see decent radiational
cooling at night with a dry air mass in place and lows will
cool into the mid 40s to low 50s. The high will be cresting over
the region on Wednesday and it should be another beautiful day
across the North Country with above normal highs and slightly
above normal lows. The high begins to break down on Thursday and
with another round potential showers and thunderstorms Thursday
afternoon into Friday.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
Through 06Z Saturday...VFR thru the period. SKC through 12Z with
westerly LLWS in the 35-40 kt range at most terminals other
than KBTV where south winds will trend gusty into the 15-20 kt
range. After 12Z south/southwest winds from 10-15 kts and gusts
from 18-28 kts expected at all terminals. SCT/BKN mid level cigs
in the 070-120 AGL range to push east across the area in the
15-22Z time frame, though no precipitation other than an
isolated sprinkle is expected with these clouds. After 00Z south
to southwest flow from 8-12 kts continues, though less gusty.
SCT/BKN cigs in the 050-080 AGL range expected with an
increasing threat of -shra toward the end of the forecast
cycle, especially at northern terminals of KMSS/KPBG and KBTV.

Outlook...

Saturday: Mainly VFR, with local MVFR possible. Chance SHRA,
Slight chance TSRA.
Saturday Night: Mainly VFR, with areas MVFR possible. Chance
SHRA.
Sunday: Mainly VFR, with local MVFR possible. Chance SHRA, Likely
TSRA.
Sunday Night: Mainly VFR, with local IFR possible. Chance SHRA.
Memorial Day: Mainly MVFR, with areas VFR possible. Chance SHRA,
Chance TSRA.
Monday Night: Mainly VFR, with local IFR possible. Chance SHRA,
Slight chance TSRA.
Tuesday: Mainly VFR, with local MVFR possible. Slight chance
SHRA.

&&

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

&&

$$
SYNOPSIS...JMG
NEAR TERM...JMG
SHORT TERM...Deal
LONG TERM...Deal
AVIATION...JMG



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