Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 291805

Area Forecast Discussion
National Weather Service Burlington VT
205 PM EDT Wed Jun 29 2016

An upper level low pressure system moving from west to east across
the North Country this afternoon and evening will bring scattered
showers and thunderstorms. Locally heavy downpours and small hail
will be possible with the stronger storms. High pressure then
builds into the Northeastern United States for Thursday with drier
and mostly sunny conditions. High temperatures will generally
range from the upper 70s to lower 80s, with lower humidity levels.
Another frontal system brings active weather for Friday, with
afternoon showers and thunderstorms expected. Some storms may
become strong to locally severe, along with heavy downpours. The
Independence Day weekend outlook looks mostly dry and favorable
for outdoor plans.


As of 149 PM EDT Wednesday...Slow-moving upper low with H5 vort
axis across the St. Lawrence Valley at 13z will progress slowly
ewd across the North Country today. Associated cold pool with
500mb temps -15C to -16C will contribute to low wbz heights
(7-8kft) and developing surface-based CAPE values of 500-1000
J/kg. Should see development of scattered showers and
thunderstorms with peak daytime heating, and added in potential
for small hail into the Wx grids. In terms of hydrology, storms
will potentially be slow-moving (propagating vectors generally NE
5-10kts), and PW values remain 1.1 to 1.2" per RAP-based SPC
mesoanalysis. Better PW axis has shifted ewd into NH/ME. Can`t
rule out some isold hydro issues this aftn/eve with possible
localized flooding, especially in the existing heavier rainfall
footprints across the nrn Adirondacks and n-central into nern VT
from yesterday`s storms, but anticipated coverage of heavier
storms doesn`t warrant a flash flood watch attm. Will continue to
monitor. Looking at highs in the mid-upr 70s today, with dewpoints
in the low-mid 60s.

Cold front and its windshift clears the area early tonight with
high pressure ridging into the area. Should see strong radiational
cooling and dewpoints dropping once diurnal clouds/showers burn
off to clear skies. Given that many areas saw at least some rain
and with winds being so light, I`d expect there to be at least
some radiational fog in the prone river valleys. It may
potentially extend elsewhere, but for now I`ve included patchy fog
for just the river valleys tonight. Lows range from mid/upper 40s
in the Adirondacks to the mid to upper 50s in the Champlain


As of 403 AM EDT Wednesday...A weak ridge of high pressure will
build east from the Ohio valley and Great Lakes on Thursday and
will remain over the region through early Friday, with fair and
dry weather expected. On Friday, models showing an upper trough
and a cold front swinging southeast across the Great Lakes. Models
also showing this upper trough will pull additional moisture
northward from the mid-Atlantic states on Friday. GFS model
showing deep layer shear of 35-40 knots in the 0-6km layer by
Friday afternoon, as well as most unstable cape values of
1500-2300 j/kg by late Friday afternoon. SPC has the region in a
marginal risk for severe thunderstorms Friday afternoon. Will hold
off on any enhanced wording for Friday at this time, and will let
later shifts reevaluate this. Shower and thunderstorm activity to
continue into early Friday night.


As of 403 AM EDT Wednesday...An upper trough will linger over the
region on Saturday, so will keep in a chance for showers. Could be
some residual showers on Sunday near the international border, but
most of the region should remain dry on Sunday. Models in good
agreement from Sunday night through Tuesday as a ridge of high
pressure builds into the region, with fair and dry weather


.AVIATION /18Z Wednesday THROUGH Monday/...
Through 18Z Thursday...Scattered shower and thunderstorm activity
mvg eastward across the North Country this afternoon and early
this evening. Will see localized MVFR to IFR conditions with heavy
downpours, with small hail also possible in strongest convection.
Convective activity generally clears the region to the east after
01z Thursday. Aside from the tstm activity, winds are generally
light W-NW at 5-8kts, and will become light and variable tonight.
Expect to see patchy dense fog development tonight, especially for
MSS/MPV/SLK between 04-11Z. Generally VFR for the daylight hrs
Thursday with light westerly winds.

Outlook 18z thursday through Monday...

18z Thursday through 12z Friday...VFR except localized LIFR
radiational fog likely at MPV and SLK 06-12Z Friday morning.

12z Friday through 12z Saturday...VFR trending MVFR/IFR as a cold
front brings scattered showers and possible strong thunderstorms
during Friday afternoon. Convective activity should move east of
the region and diminish Friday night.

12z Saturday through Monday...Mainly VFR, except few -SHRA
possible nrn mountains Saturday aftn/early evening.


Scattered shower and thunderstorm development ongoing this
afternoon as 500mb low and associated thermal trough (-15 to -16C)
shifts slowly ewd across the North Country. NAM soundings suggest
slow-moving activity, with NEWD propagation/MBE vectors of
5-10kts. Consistent with that, have seen training thunderstorms
with radar estimated rainfall of 1 to 2" across Grand Isle county
and also across Eastern Essex NY on wrn shore of Lake Champlain.
Air mass remains unstable ewd across VT this aftn into this
evening with SBCAPE values generally 500-1000 J/kg. PW values are
a bit lower today, generally 1.1 - 1.2" and 3-hr flash flood
guidance of 2 to 3" most sections. Can`t rule out some localized
flooding concerns this afternoon and evening, but mainly across
the areas that observed heavier rainfall yesterday (namely
portions of srn Franklin NY into wrn Clinton counties, and also
across Orleans, Caledonia, and Essex counties in VT). Will
monitor convective and radar trends through the afternoon and
evening hours.




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