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Area Forecast Discussion (AFD)

Issued by Burlington, VT (BTV)

                            
376 
FXUS61 KBTV 191423
AFDBTV

Area Forecast Discussion
National Weather Service Burlington VT
1023 AM EDT Wed Sep 19 2018

.SYNOPSIS...
Morning clouds will give way to partial sunshine this afternoon
as high pressure and it's cooler airmass settle south across 
the region. Temperatures gradually warm by Thursday into Friday 
before a strong cold front and associated showers push through 
the area Friday evening. Behind this front cooler and drier 
weather are expected for the upcoming weekend.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 1023 AM EDT Wednesday...Forecast for the rest of today
remains in excellent shape with the main idea of clouds
gradually scattering out and temps rising into the 60s still
looking good.

Previous Discussion... Variable cloud cover continues to advect
slowly south into the forecast area this morning behind a 
departing early fall cold front. A secondary, back door front is
also pushing southwestward across eastern New England and will 
reach the CT River Valley by sunrise with additional clouds and 
perhaps spotty drizzle under a more maritime airmass. The 
forecast challenge today will be how soon these clouds mix out 
and the degree to which boundary layer warming governs 
temperature maxima. I feel the NAM output continues to 
exaggerate the strength of the frontal inversion and it's much 
cloudier/cooler thermal profiles are too pessimistic, especially
west of the Greens. Time will tell but for now have leaned more
toward a model-blended solution showing skies trending partly 
sunny by afternoon in most areas with temperatures ranging 
through the mid and upper 60s under modest boundary layer 
mixing. It is September, not December.

By tonight weak surface high pressure bridges into the area with 
large scale height rises aloft. Winds will be light north to 
northeasterly, with occasional clouds being most prevalent across 
eastern VT counties under lingering maritime airmass affects. Again, 
some spotty drizzle may be possible in these areas. Low temperatures 
a blend of mainly bias-corrected guidance ranging through the 40s to 
around 50, though locally milder near Lake Champlain.

By Thursday surface to mid level ridging continues across the area 
with light north to northeasterly winds tending to veer more 
east/southeasterly toward evening in advance of our next system. 
Partly sunny skies should be the rule with some broad increase in 
mid to upper level cloud cover across northern NY toward day's end. 
Temperatures to moderate slightly with max values mainly from the 
mid 60s to lower 70s.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 300 AM EDT Wednesday...A low pressure system will track from 
the northwestern Great Lakes Region to central Quebec Friday, 
pushing a series of fronts through New England that will control the
short term forecast. Plenty of baroclinicity associated with 
the early fall system, so should see some impressive temperature
advection over the area Friday. The cyclone's warm front will 
cross the forecast area Thursday night through Friday morning, 
spreading some rain through the North Country as it does so. 
Very little dynamic support in the upper-levels over our area 
(much more impressive further north...), but a broad area of 
synoptic-scale ascent from isentropic lift will ensure that most
areas see at least some measurable rain. Given the strength of 
the impressive 50+ kt LLJ within the warm-sector of the cyclone,
QPF will vary greatly with terrain. The Saint Lawrence Valley 
should see the most precipitation under this setup, while much 
of the Champlain Valley will get rain- shadowed, resulting in 
significantly lower QPF amounts. Overall for many areas, should 
be a higher PoP/lower QPF scenario. Some marginal (<500 J/kg) 
elevated CAPE will be present over northern New York, so an 
isolated rumble of thunder Friday morning can't be ruled out. 

Winds Friday will be quite gusty from the south/southwest. Strongest 
winds will be at highest elevations and in channeled valleys. 
Areas of the Saint Lawrence Valley and the Champlain Valley will
see gusts in excess of 25 mph during the afternoon hours as 
higher momentum air within the LLJ is mixed to the surface. 

High temperatures Friday will be highly variable across the CWA. 
Strong warm air advection will allow temperatures to climb into
the low 80s in the Saint Lawrence Valley. The Champlain Valley 
should also warm up quite a bit, with highs near or at 80 
degrees not out of the realm of possibilities with strong 
downsloping southwesterly winds in place. Areas east of the 
Green Mountains, however, will be noticeably cooler, topping out
in the upper 60s to low 70s.

Friday night, the system will sweep a strong cold front through
the area, reinvigorating shower activity. Better dynamics aloft
associated with this frontal passage, however best upper 
support does lag quite a bit behind the frontal passage. Given 
the overnight timing of the frontal passage and the subsequent 
lack of much instability, along with the offset of surface 
forcing and upper-level support, not overly impressed at this 
point with thunderstorm potential. If any thunderstorms are able
to develop along the front however, the strong shear/flow aloft
could support some gusty winds reaching the surface. Once 
again, best chances of an isolated thunderstorm or two would be 
in the Saint Lawrence Valley, where the earlier timing of the 
frontal passage would line up with better instability.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 300 AM EDT Wednesday...Weather turns more benign, but 
noticeably cooler, this weekend as we settle into fall-like 
conditions behind the cold front. Highs Saturday and Sunday will 
only be in the low to mid 60s. Saturday night will be the 
coolest night in quite some time with temperatures in the mid 
30s to mid 40s expected. Areas of the Northeast Kingdom and 
northern Adirondacks will be the coldest, and should see a frost
or possibly even a freeze Saturday night. 

Monday night, high pressure will shift offshore and return southerly 
flow will advect in some warmer air. Temperatures will 
gradually climb back towards seasonal values towards the middle 
of the week. The next chance of precipitation looks to be in the
Tuesday/Wednesday time-frame as another low tracks 
northeastward through Canada, sending a warm front through the 
northeastern US.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
Through 12Z Thursday...Variable conds through 15Z, trending
mainly VFR from 15Z onward as low stratus slowly lifts. Lowest
cigs expected at KRUT and KMPV where LIFR will slowly lift to
MVFR by 15Z, then VFR from 18Z onward. Outside spotty higher
elevation drizzle, no preciptation is expected. Winds generally
light north to northeasterly from 3-8 kts today, abating to
light and variable after 00Z.

Outlook...

Thursday: VFR. NO SIG WX.
Thursday Night: Mainly VFR, with local MVFR possible. Chance
SHRA.
Friday: Mainly MVFR, with local VFR possible. Chance SHRA, Slight
chance TSRA.
Friday Night: Mainly MVFR, with areas VFR possible. Likely SHRA.
Saturday: Mainly VFR, with areas MVFR possible. NO SIG WX.
Saturday Night: VFR. NO SIG WX.
Sunday: VFR. NO SIG WX.

&&

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

&&

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