Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 231730

Area Forecast Discussion
National Weather Service Burlington VT
130 PM EDT Sat Jul 23 2016

More scattered showers and thunderstorms are expected across the
North Country today as an upper level disturbance moves through.
Some thunderstorms may have gusty winds and small hail. Sunday
looks mostly sunny and seasonable under hand yet another
possibility of showers and thunderstorms late Monday. Warm and
mostly dry summer weather looks like it will continue Tue and Wed.


As of 125 PM EDT Saturday...A line of storms just north of INTL
border moving ese will largely impact nrn VT with ne NY as well.

SPC has increased to SLGT risk and this is consistent with our
line of thinking gusty possible dmamging winds 30-50+ mph,
possible hail up to 1 inch but frequent lightning.

Made some tweaks in grids to capture perceived movement and put
some enchanced wording.

Previous Discussion...Only minor adjustments needed to the
previous forecast at this time, mainly to bump up temps a bit and
slow timing of afternoon convection a few hours for the remainder
of the morning hours. Otherwise, still looking for convection to
fire up after about 16z with the primary threat from any severe
storms that do develop being gusty winds and hail.

Previous Discussion...
Rapid cumulus cloud development expected this morning. A potent
shortwave trof see on water vapor imagery and is producing
lightning at sunrise. This trof is expected to move across our
area this afternoon with cooling aloft as 500 mb temps drop down
to -15C. This cooling aloft along with mild 850 temps of about 13C
and surface temps reaching the upper 70s to lower 80s are expected
to kick off thunderstorms this morning/early afternoon in the
north. Each model has a differing evolution of the convection, and
is again a symptom of just how sensitive the models are to this
type of weather pattern that is driven by mixed layers, elevated
and low level instability and boundary layer details.

Taking a blend of the models suggests that we`ll have CAPE values
750 to 1500 J/kg, highest in the St. Lawrence Valley which is
decent enough to drive convection. We`ll also have 30-40kt 0-6km
shear mainly over the south and west portions of our area while
shear over VT less on the order of 15 to 25 kts. So we can`t
totally rule out a stronger storm with gusty winds and small hail,
so have included in the forecast.

Looks like the highest chances 60-80% of precipitation and storms
will be from mid-day until early evening. SPC has our region
under "Marginal Risk" of severe thunderstorms and we are in good

Scattered showers/storms then wane and exit southeast fairly
quickly Saturday evening as upper trough swings through the region
and is replaced by building high pressure. Chance of precip drop
off quickly during the evening, then largely dry from midnight
onward. Low temperatures near seasonal mid- summer norms in the
50s to around 60 for most locales.


As of 419 AM EDT Saturday...Sunday: All models agree the day will
live up to it`s name and be a super spectacularly sunny and serene
day. Ridging aloft and at the surface will be in place. With 925mb
temperatures running between 17- 19C, we`ll see daytime highs
topping out in the upper 70s (higher elevations) to lower 80s
(valleys). light winds and dewpoints in the 50s will ensure
comfortable conditions. Given all that model agreement, I did not
stray from the guidance blend.

Sunday Night: Things change as ridging moves off to the east as the
next trough in the overall westerly flow starts heading our way.
Warm air advection aloft will result in increasing clouds overnight.
Should be some elevated instability as well, have noted Showalter
Index values <0C spreading in after 06z monday in the models. That
suggests showers are possible, and sure enough that is what the
models show as well. Have painted in rising chances overnight.
Expect a few showers, mainly across northern NY, prior to daybreak
Monday. A rumble of thunder is not out of the question across the St
Lawrence valley by dawn as we`ll have the nose of an 850mb jet
pushing into that area to provide a little extra lift. The
increasing clouds will keep it mild for most of the region. Low/mid
60s from the Champlain Valley westward. 50s will be confined to
eastern VT

Monday: For days, guidance has been indicating unsettled conditions
(eg: showers and t-storms) to be possible. 00Z model runs are no
different, and have come in more alignment with timing and overall
setup of convective ingredients. Still, things are not totally
clear. What I do expect is that a fairly robust shortwave will be
approaching the region late in the day. This will sync up daytime
heating with the best dynamics aloft. Models do indicate surface
based instability of probably 1000-1500 J/kg (NAM as typical is
higher) due to a warmer and more humid airmass getting into place.
Just how much instability we achieve will be related to how much sun
we see. 925mb temperatures are expected to become very warm -perhaps
23 to 25C. Under perfect atmospheric mixing conditions, this would
result in temperatures at the valley floor pushing into the mid 90s!
However, it appears we`ll have a good amount of clouds to restrict
heating to a degree. Though we should still easily reach the mid
80s.  The 0-6km bulk shear values are in the marginal level for
getting storms to become on the strong side.  SPC does have the
region in a marginal risk, but they also have some concerns about
the mix of ingredients lining up perfectly to develop severe t-
storms. Evaluation of various forecast sounding for Monday have some
"goofiness" (thats a technical term, by the way) showing in the
profiles. Not sure if that is due to convection within the models,
or if it`s a sign that despite the very warm air aloft, we`ll have
some inversion in place to restrict mixing, which in turn means
restricted convection.  At this point, will play the middle ground,
and keep PoPs in the 40-55% range and see how future guidance trends.

Monday Night: Whatever convection we do see, will be pushing out of
the region as the night goes on. Will likely be warm and muggy with
lows in the 60s.


As of 419 AM EDT Saturday...Decent agreement with the 00z suite
of models, and much of the week should be relatively quiet, but
feature more or less typical summer weather. Most of the week
we`ll see temperatures running a bit above normal. Looks sunny and
warm for both Tuesday and Wednesday. GFS and ECMWF start to advect
in some moisture for Thursday, along with having a little more
troughiness develop and perhaps a weak front sliding down from
Quebec. Thus it appears we`ll see some showers and t-storms
around. At this point, they appear to be of the garden variety as
I don`t see strong dynamics in place. Kept with a model blend and
painted in 30-40% PoPs. More uncertain for Friday. 00Z runs vary
from 12z guidance and keep in clouds/showers rather than having
things clear out more. Really don`t have any confidence, so just
went with the full blend with temperatures close to normal and low
chances of showers.


.AVIATION /18Z Saturday THROUGH Thursday/...
Through 18z Sunday...Mainly VFR but scattered brief MVFR/IFR in
stronger showers and thunderstorms moving n to s thru 23z. High
pressure starts to move in from the NW overnight with light winds
and patchy dense fog and LIFR forming again 06-12Z at KSLK and

Winds generally light west to northwest at 5 to 10 knots.

Outlook 18z Sunday through Tuesday...

Sun...Mainly VFR under weak high pressure.

Mon/Monday night...VFR with scattered brief MVFR/IFR in showers
and thunderstorms with frontal passage.

Tuesday...VFR/high pressure.




NEAR TERM...Lahiff/Sisson/SLW
AVIATION...Sisson/SLW is the U.S. government's official web portal to all federal, state and local government web resources and services.