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  Tuesday May 23, 2017

 

NWS Area Forecast Discussion


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FXUS61 KBTV 221934
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
334 PM EDT Mon May 22 2017

.SYNOPSIS...
A weak cold front crossing New York and Vermont through this evening
will bring isolated showers, along with lingering low clouds and
areas of fog overnight. Will see clearing Tuesday with a weak
area of high pressure in place across the northeastern U.S. and
temperatures moderating back into the upper 60s to lower 70s. A
few afternoon showers are possible Wednesday, but high
temperatures will continue to moderate into the low to mid 70s.
A large mid-level trough across the Tennessee and Ohio Valleys
and associated developing surface low pressure will bring
increasing chances for widespread rainfall across the North
Country on Thursday and Friday.

&&

.NEAR TERM /THROUGH TUESDAY NIGHT/...
As of 138 PM EDT Monday...Secondary surface trough axis
shifting ewd across central NY/PA is associated with two bands
of shower activity. The first is moving ewd across wrn/central
VT at 1730Z. The second band of showers is across the Mohawk
valley of NY at 1730Z, and is expected to expand nwd across the
northern Adirondacks and shift across VT late this afternoon.
Not expecting anything too significant in terms of QPF...with
an additional 0.05 - 0.10" rainfall on top of the 0.3-0.5" that
generally fell during the overnight/morning hours.

Will see some gradual mid-level drying this evening (above
750mb) with WSWLY flow aloft, but pronounced low-level inversion
should continue to hold low stratus in areawide with overcast
skies and cool temperatures. Afternoon highs only expected to
range from the lower 50s east of the Green Mtns, to near 60F at
BTV, and upr 50s to lower 60s across nrn NY. The KCXX vad wind
profile still indicates 25-30kt flow at 2-3kft AGL. Won`t fully
see these winds at low elevations due to stability, but
occasional gusts to 20-25 mph are possible thru this aftn.
Expect winds remaining 20-25kts over the broad portion of Lake
Champlain, and the Lake Wind Advisory continues there.

Tonight through Tuesday a weak surface ridge builds into the
region. Lowering inversion and light surface winds, along with
moist ground from recent rain will promote fog formation in the
usual areas. During this time flow aloft remains southwesterly,
and low pressure over the Great Lakes will ride through the 500
mb ridge, suppressing the ridge & shifting it east. The low
passes well enough north that the surface ridge will win out
with no rain during this time, but will still be quite a few
clouds around. Tuesday about 10 degree warmer than monday with
highs in the 60s/near 70.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 315 PM EDT Monday...12z guidance suite still indicating
that Wednesday will be the warmest day of the entire weak. Weak
ridging aloft will put the region into a col area (light flow
regime). Hi-res models do hint at just enough low level moisture
and surface instability will exist to pop a few showers,
primarily across the higher terrain in the afternoon, though
with an inversion around 15,000ft not expecting any t-storms to
develop. Winds from 10,000ft down to the surface will be
generally 10 knots or less, so look for onshore lake breezes to
develop. 925mb temperatures will be running about 17C, which
given a decent amount of sunshine will result in lower elevation
temperatures within a couple of degrees of 80F.

Wednesday night flow starts to turn south/southeast as low
pressure moves toward the Great Lakes. Models all show an area
of deeper moisture moving toward the region, so as we move
toward daybreak Thursday it appears precipitation will be
starting to overspread the region. Have depicted a ramping up of
PoPs up well after midnight, though most of the night will be
dry.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
As of 315 PM EDT Monday...12z guidance came in fairly close to
previous runs, thus confidence remains rather high for the
overall scenario of unsettled weather through much of the
period. Looks like the primary rounds of more significant
weather will be Thursday and again Monday (Memorial Day), with
"okay" weather squashed in between. Comments on each day
follow...

Thursday: Fairly sizeable low pressure will be moving across the
Ohio Valley with a deepening upper level trough also in place.
This will result in a tightening pressure gradient with a
low/mid level east-southeast jet developing during the day. The
GFS indicates about 40-45kts of wind at 850mb, with the 12z euro
having a few grid points of 50kts of wind. Fairly typical
situation in which we`ll probably have some breezy conditions
along the western slopes of the Green Mountains. At this point
think we could max out with some gusts in the 30-40 mph range in
the favored areas. Lower resolution global models don`t have a
very good depiction of these localized effects, so did try to
manually introduce some gustier winds into the gridded database.
Just an aspect of the forecast we will have to monitor.

Otherwise, system will have a pretty good moisture tap
(precipitable water values about 1.3"), so expect fairly
widespread rainfall to occur during the day with rainfall totals
probably around 1/2". Shouldn`t lead to any hydro issues, but
also another aspect to monitor. Kept with a model blend for
temperatures, which has primarily 60s across the region (lower
60s across southeast VT to upper 60s around 70 for the northern
Champlain Valley into the St Lawrence Valley), however it may
end up cooler than that if we inject more Atlantic airmass into
the region.

Friday: The upper trough turns into a closed low and moves
across the region during the day. Basically means a continuation
of unsettled conditions with spotty showers at times. Lots of
clouds will keep it on the cooler side once again, generally in
the 60s.

Saturday: Trough and surface low move off to our east, putting
us into a northwest flow situation. 850mb temperatures start off
around 5-7C and by afternoon rise to 9C. This should support
highs in the upper 60s to lower 70s, though if we can see more
sunshine, mid 70s are possible. Still can`t rule out an isolated
shower, but should be pretty good for most outdoor activities.

Sunday: GFS hints at a weak back-door cold front trying to come
at us from the east as surface high pressure moves over Maine
and sets up some low level easterly flow, with the chance for a
few light showers. The 12z ECMWF has no such feature, and is
putting the region into a developing southerly flow situation
ahead of Monday`s weather maker. However, with that deeper
southerly flow, it`s got some deeper moisture.

The net result from either type of scenario is that showers
can`t be ruled out for Sunday at this point. Not as much
confidence in the temperature forecast however, and given the
variation in scenarios we could be anywhere from the upper 60s
to lower 80s for highs. Stuck with a blend for this go around.

Monday: Alas, Memorial Day isn`t looking the best for those
outdoor BBQs/games/parades etc if you want to avoid any rain.
Another fairly robust trough will be swinging across the region,
though the GFS and ECMWF differ on details relating to placement
of surface low and timing. In either model`s scenario, we`ll
have scattered showers around. GFS is more robust in pushing
some more humid airmass into the region from the south, with
enough instability to fire off a few non-severe t-storms during
the afternoon. ECMWF has much less instability, but still a
signal that a rumble of thunder can`t be ruled out. Have gone
ahead and placed some slight chance probability of thunderstorms
in the forecast. Stuck with the blended approach for high
temperatures, with highs generally around normal (upper 60s to
lower 70s). Not great confidence on that aspect at this point.

&&

.AVIATION /19Z MONDAY THROUGH SATURDAY/...
Through 18Z Tuesday...Main aviation wx concern will be low
cloud trends and possible fog overnight, especially during the
pre-dawn period (06-11Z). Overall, abundant MVFR to IFR
ceilings (low stratus deck) expected through 12Z Tuesday. A weak
sfc trough/cold front crossing the region from west to east
will bring isold -SHRA 21-03Z. Thereafter, a weak sfc ridge
will build newd from wrn NY and wrn PA. This will allow for
diminishing winds and lowering ceilings (with strong inversion
layer in place) into the IFR category 03-12Z Tuesday with TRRN
OBSCD. The one exception should be KMSS. At KMSS, should see
just enough SW flow (5-8kts) to keep PBL mixed precluding low
cloud and fog development locally there. At the other TAF sites,
may see some patchy fog around, especially during the pre- dawn
hours with periods of LIFR conditions possible 08-12Z. Winds
generally south around 10kts through 02-03Z Tuesday. Thereafter,
winds will shift into the SW-W with sfc trough passage. Should
see improving CIG/VSBY conditions with ceilings lifting back to
VFR by 13-15Z and skies trending SCT-BKN. Winds will be
relatively light during the daylight hours on Tuesday, generally
W-SW at 5-8kts.

Outlook...

Tuesday: VFR. Patchy morning FG.
Tuesday Night: VFR. NO SIG WX.
Wednesday: VFR. Slight Chance SHRA.
Wednesday Night: VFR. Chance SHRA.
Thursday: VFR. Breezy. Likely SHRA.
Thursday Night: VFR/MVFR. Likely RA.
Friday: MVFR. Likely RA.

&&

.MARINE...
As of 145PM Monday...Southerly winds 15-25kts across Lake Champlain
will diminish and shift into the southwest early this evening.
The Lake Wind Advisory will likely be cancelled late this
afternoon or early this evening.

&&

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

&&

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



 
 
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