Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 290736

Area Forecast Discussion
National Weather Service Burlington VT
336 AM EDT Thu Jun 29 2017

The combination of a warm front shifting through the region today,
and a cold front following on Sunday will bring several rounds
of showers and thunderstorms over the next few days with
increasing humidity through the weekend. Locally heavy rain is
possible through Saturday, with increasing potential for
isolated flash flooding. Drier weather returns for Monday and
Independence day.


As of 336 AM EDT Thursday...Forecast for the next 36 hours
remains largely unchanged from the previous days thinking with
the highlight being an increasing threat for flash flooding due
to wet antecedent soils and heavy rainfall.

For today, low pressure moving through the Great Lakes will
push a warm front over the region with showers developing across
northern New York this morning, and becoming widespread across
the entire forecast area through the afternoon hours and into
the first half of tonight. Instability is rather meager through
the low/mid levels for much of the day limiting thunderstorm
potential, but as the front begins to lift northward towards the
international border tonight, steeper low/mid level lapse rates
develop along with slightly increased surface instability so
will keep the chance of thunder in the forecast. In addition,
initial surge of PWAT plume of 1-1.5" moves over the region late
this afternoon through midnight or so, increasing the threat
for some localized heavy rain.

Note a little slower northward movement of the front on the
latest guidance this morning, likely bisecting the North Country
from west to east across central zones Friday morning, and
lifting north of the international border around mid-day.
Overnight shower and thunderstorm activity wanes a bit during
the pre-dawn to mid-day hours before the region becomes firmly
entrenched in the warm sector in the afternoon with some
diurnally and surface instability driven convection expected to
develop with the threat for heavy rain continuing to increase
as PWATs rise to 1.5-2".


As of 316 AM EDT Thursday...By Friday night we remain embedded
within an anomalously moist airmass under deep southwesterly
flow aloft. PWATS in the 1.5 to 2.0 inch range argue for
continue higher chances for showers and few thunderstorms. With
lack of appreciable instability, feel the threat of heavier
rainfall will wane somewhat but spotty heavy downpours will
certainly be possible with any passing showers. Lows to hold
quite mild in the 60s to locally near 70 in the Champlain and
St. Lawrence Valleys.

By Saturday another round of active weather is appearing more and
more likely as deep moisture plume remains atop the area along with
increasing instability ahead of an advancing upper trough and
attendant surface front. Deep warm cloud depths and near-
unidirectional flow aloft enhance the potential for heavy
rainfall and training characteristics will be possible. This
will heighten the possibility for flash flooding, though given
the mesoscale aspects of such phenomena it is too soon to
predict where the highest threat will exist. It will remain warm
and quite muggy as afternoon highs top out in the 80s.


As of 316 AM EDT Thursday...Evening showers and thunderstorms,
some with heavy rainfall then slowly lessen in coverage Saturday
night as surface front pushes east. Lows remain mild in the

By Sunday into Monday of next week longwave trough pivots into the
area with several additional spokes of energy affecting the area.
Airmass will trend seasonably drier over time as humidity levels
drop to noticeably more tolerable levels. That said, will hold onto
chance pops for a few showers in this period, especially during
daylight hours when surface heating will aid to steepen lower to mid
level lapse rates and aid buoyancy.

By the middle of next week conditions appear to trend bodily drier
as longwave trough departs east and is replaced by building high
pressure at the surface and aloft. Temperatures should average close
to early July norms.


Through 06Z Thursday...Mainly VFR is expected through overnight
hours with patchy fog possible at KMPV, then conditions
deteriorate as rain showers shift into the region after 12Z.
Ceilings remain largely VFR through sunset with periods of MVFR
vsby likely in heavy showers, then after 00Z cigs/vsby both
lower to MVFR. Winds should be fairly light through the period
generally out of the south 5-10 kts.


Friday: VFR. Breezy. Likely SHRA...Slight Chance TSRA.
Friday Night: VFR. Chance SHRA...Slight Chance TSRA.
Saturday: VFR/MVFR. Likely SHRA...Likely TSRA.
Saturday Night: VFR. Chance SHRA...Slight Chance TSRA.
Sunday: VFR. Chance SHRA.
Sunday Night: VFR. Slight Chance SHRA.
Monday: VFR. Slight Chance SHRA.


As of 336 AM EDT Thursday...A very wet period is expected over
the next several days with average rainfall amounts of 1.5-2.5"
forecast through Saturday night. With streamflow values above or
much above normal as of this morning, there is little if any
storage available and much that falls over the next several days
will go straight to runoff. Any potential flooding
Thursday/Friday will be limited in areal coverage, but will
potentially set the stage for flooding Saturday and Saturday
night by leaving saturated antecedent soil conditions.




NEAR TERM...Lahiff
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