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  Tuesday May 23, 2017

 

NWS Area Forecast Discussion


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000
FXUS61 KBTV 211908
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
308 PM EDT Sun May 21 2017

.SYNOPSIS...
Surface high pressure will translate east of New England this
evening allowing a warm front to push into the North Country
from the eastern Great Lakes region. We will see periods of
rain developing this evening across northern New York, and
during the overnight hours across central and northern Vermont.
Lighter rain showers and overcast skies will linger during the
day Monday, resulting in relatively cool temperatures. Rainfall
amounts between one-third and one-half inch are generally
expected across the North Country tonight into Monday morning.
Dry conditions return on Tuesday with a brief period of surface
high pressure.

&&

.NEAR TERM /THROUGH MONDAY NIGHT/...
As of 231 PM EDT Sunday...At 18Z, strong sfc anticyclone
extended from the Gulf of St. Lawrence southward across ern New
England. This system has brought dry low-level conditions and
light winds to the region thus far today. This system tilts
westward with height, and have seen building 700-500mb heights
throughout the afternoon across nrn NY and VT. That said, there
is abundant mid-upper level moisture entrained in
anticyclonically curved flow aloft, which will yield mostly
cloudy skies/filtered sunshine through the remainder of the
daylight hrs late this aftn/early this evening. Temperatures
have risen into the upper 60s to lower 70s, with dry low-level
air mass in place (2-m dewpoints in the low-mid 30s).

Mosaic composite radar reflectivity indicates axis of
steady/moderate rainfall across sern Ontario swd across far wrn
NY/wrn PA and ern OH at 1830Z. There are some leading echoes
east of Lake Ontario into St. Lawrence County NY, which will
bring a few light sprinkles or isold -SHRA across nrn NY late
this afternoon/early this evening. However, bulk of steady
precipitation doesn`t reach nrn NY until after 00Z, with onset
of stronger 850-700mb WAA and isentropic ascent approaching from
the SW. Mesoscale models, including the HRRR/BTV-4km WRF and
NAM-Nest all show rainfall reaching the Champlain Valley by 03Z
or so, and far ern VT by 05-06Z. Anticipate a 5-6hr period of
rainfall, yielding amts generally between 0.33-0.50" thru early
Monday morning. Will also see increasing P-gradient overnight.
This will result in low-level channeling of winds in the
Champlain Valley, with gusts locally up to 30 mph in the BTV
area. A Lake Wind Advisory has been issued for Lake Champlain
beginning at midnight as south winds increase to 15-25kts during
the pre-dawn hrs. Overnight lows will generally be in the mid-
upr 40s tonight.

Best large-scale forcing slides to our east between 12-15Z
Monday, but NAM RH profiles indicate continued saturated
conditions in 950-850mb layer, and skies will generally remain
cloudy with low overcast in place. The low-level inversion
layer in place will keep sfc temps cool, despite 850mb thermal
ridge in place (+10C to +11C) across nrn NY. Sfc high temps
generally low- mid 50s east of the Greens, upr 50s in the
Champlain Valley, and upr 50s to lower 60s across nrn NY.
Maintained a chance of showers Monday afternoon. There is some
indication of a trailing sfc trough/convergence line moving ewd
across nrn NY into VT late in the afternoon, which may result in
an additional period of (brief) rain shower activity.

A weak sfc ridge builds newd into our region from western NY
Monday night. This results in lowering inversion layer and light
near-sfc winds. With moist soils, will see combination of
abundant low clouds and patchy fog areawide. Moist layer is
quite shallow, so not anticipating any precipitation. Lows
Monday night mainly 43-48F.

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
As of 325 AM EDT Sunday...Broad southwesterly upper level flow
across the region during the short term period with high
pressure giving way to a coastal low on Wednesday. Monday night
lingering chance pops in Vermont will trend downward to nil by
midnight as weak front departs the region. Little airmass change
behind the boundary, and low level winds return to southerly by
mid day Tuesday. Tuesday weak surface high pressure will keep
precipitation at bay, however periodic vort maxes eject out of
base of 500 mb trough to west will traverse the area keeping
scattered to broken sky cover. One shortwave trough moving up in
the southwest flow will spin up a surface low Wednesday morning
along the Delmarva coast and move it northeast to southern New
England coast Wednesday evening. Chance pops across the
region...ECMWF spreads precip shield further west than GFS, and
expect to further refine this part of the forecast in coming
days. Southwesterly flow will also keep seasonable temperature
in place with highs in the 70s and lows in the 40s to lower 50s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 325 AM EDT Sunday...Long term period becomes more active
as the upper trough to the west shifts east, spreading
precipitation into the area. Model differences seen last night
are starting to coalesce into a common solution. Mean upper
level trough over eastern US will move east in two phases. First
is southern low moving out of Gulf states will swing northeast
Thursday, spreading more showers up the east coast. The northern
portion of the trough will hang back over the Great Lakes, then
move east and merge with the southern low remnants over the
gulf of Maine on Friday. The result is a prolonged period of
likely pops for rain Thursday and Friday. With all the pieces in
motion there should be some breaks at some point in there, but
difficult to tease out those details this far out.

For Saturday the low finally kicks out with building high
pressure. Some lingering showers especially in Vermont in the
mountains, but trend will be to salvage at least part of the
Memorial Day weekend.

Plenty of cloud cover and rain cooled air to keep temperatures
a few degrees below normal but still seasonable. Overall flow
through this period is southwesterly as well, and no real
temperature changes.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
Through 18z Monday...Mid-level cloud cover (BKN-OVC100-150)
will spread ewd across the TAF locations this afternoon and
early this evening. Will see a gradual lowering of cloud
ceilings through the evening with increasing chances for rain
showers, especially during the overnight hrs. After midnight,
should see development of MVFR ceilings (2-3kft) at SLK/MSS,
along with HIR TRRN OBSCD areawide and vsby 4-5SM at times in
showers and BR. There is a chance of MVFR ceilings at the
remaining TAF locations, but anticipate predominantly 3-4kft
ceiling heights for RUT/BTV/PBG. Should see MVFR developing at
MPV by 14Z/Mon.

Winds generally less than 10kts through 06Z. Thereafter, should
see some gusts from the south approaching 20kts at BTV/PBG as
gradient flow strengthens toward daybreak.

Outlook...

Monday Night: MVFR ceilings with isold IFR in FG. Chance SHRA.
Tuesday: VFR. NO SIG WX.
Tuesday Night: VFR. NO SIG WX.
Wednesday: VFR. Chance SHRA.
Wednesday Night: VFR. Chance SHRA.
Thursday: VFR/MVFR. Likely SHRA.
Thursday Night: VFR. Likely SHRA.
Friday: MVFR. Likely SHRA.

&&

.MARINE...
A Lake Wind Advisory is in effect starting at midnight (04Z
Monday). Gradient flow increases out of the south during the
pre- dawn hours Monday, with sustained winds over Lake
Champlain reaching 15-25kts after midnight and waves building to
2-4 feet. The highest waves are expected across the northern
portion of the broad lake south of Grand Isle. South winds will
remain generally in the 15-25kt range during the daylight hours
on Monday, before diminishing Monday evening.

&&

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

&&

$$
SYNOPSIS...Banacos
NEAR TERM...Banacos
SHORT TERM...Hanson
LONG TERM...Hanson
AVIATION...Banacos
MARINE...Team BTV


 
 
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