Area Forecast Discussion
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FXUS61 KBTV 302356
Area Forecast Discussion
National Weather Service Burlington VT
756 PM EDT Thu Jun 30 2016
High pressure remains in control across the North Country this
evening and overnight with mainly clear skies and light winds. A
frontal system approaching from the Great Lakes region will bring
widespread showers with embedded thunderstorm activity Friday
afternoon into Friday evening. A few strong to severe storms are
possible with hail, gusty winds, and locally heavy rainfall. The
frontal system ushers in cooler air for Saturday, with high
temperatures only in the upper 60s to lower 70s. A few showers are
also possible across the Northern Mountains on Saturday.
Increasing sunshine and dry conditions are forecast for Sunday and
the Independence Day holiday.
.NEAR TERM /THROUGH FRIDAY NIGHT/...
As of 756 PM EDT Thursday...Beautiful early summer weather
expected for tonight with clear skies, light winds and seasonable
temperatures. Other than some nominal tweaks to winds with latest
LAMP output the forecast remains largely unchanged. Held onto some
patchy fog in favored locales, though this should be fairly
limited in duration and areal coverage given the nocturnal period
is near its yearly minimum. Have a great evening.
Prior discussion from 224 PM EDT Thursday...
Main focus during the near-term period is potential strong to
severe thunderstorms and localized heavy rainfall for Friday
afternoon into Friday evening.
Tonight: Conditions will remain tranquil in the meantime with
ridge surface and aloft in place this evening and through much of
the overnight. Some flat fair weather cumulus clouds dotting the
higher terrain will dissipate with onset of diurnal cooling cycle
this evening, setting up clear skies and good radiational cooling
overnight. Winds are generally light through the overnight, but
will see light S-SE flow develop from the Champlain Valley wwd
toward daybreak as surface low moves ewd across lower Michigan,
and high pressure shifts east of New England. With generally light
winds, should see some patchy fog develop after 04-05Z in the
deeper valleys within the northern Adirondack region and
central/ern VT. That said, increase in 925mb flow to near 15kts
toward daybreak may cause some increased low-level mixing and
preclude fog from becoming dense or very widespread. Overnight
lows generally in the low-mid 50s, except locally in the upr 50s
near Lake Champlain with developing south winds...and also in the
mid-upr 40s in the nrn Adirondacks given current dewpoint
Friday: Vigorous mid-level trough across lower Michigan at 12Z
will shift enewd with increasingly cyclonic flow and height falls
across nrn NY into VT during the afternoon and early evening
hours. Low-mid level wind fields become moderately strong with sfc
to 6km bulk shear reaching 30kts by 18Z and around 35kts at 21Z.
Strong differential PVA moving into nrn NY coincides with best
insolational heating, which should aid in low-level lapse rates
and convective initiation. Given strength of forcing for ascent,
not much question on development of showers and embedded tstms
across nrn NY and s-central VT beginning around 18Z, and then
spreading ENEWD across the Champlain valley mid-late afternoon,
and central/ern VT late afternoon into the evening hours. Have
included PoPs 80-90% during the peak heating hrs.
Primary limiting factor for widespread severe wx will be limited
moisture return. Current 2-m dewpoints generally upr 40s to lower
50s across the region, and expected to rise into the upr 50s by
early after Friday. These moisture values combined with high temps
in the upper 70s to lower 80s will contribute to fairly modest
SBCAPE peaking around 1000 J/kg. That said, believe incipient
updrafts can make use of excellent low-level hodograph structure
(0-1km SRH around 200 m2/s2 at BTV per NAM-12km) and favorable
deep- layer shear for a few rotating storms, which can augment
relatively low CAPE profiles. As such, will carry enhanced wording
at this time with hail and gusty winds mentioned in the forecast.
Depending on overall convective evolution, will need to watch for
any training cells across the nrn Adirondacks and n-central/nern
VT where soils remain moist from rainfall past 48-72 hrs (see
hydro section below for additional details). Overall QPF amts
generally 0.50 to 0.75", but could see some locally higher
footprints with any training thunderstorms. 3-hr FFG generally
Friday night: 700-500mb shortwave trough acquires negative tilt
across VT Friday evening, with going strong convective activity
exiting across ern half of VT between 00-03Z. Thereafter, surface
frontal passage brings westerly wind shift and lingering
clouds/isold showers overnight. Low temperatures generally in the
.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 328 PM EDT Thursday...Saturday and Saturday night we`ll see
our typical post frontal regime with the aforementioned upper low
settling up over the area post frontal passage. The morning should
begin dry with a mid-level dry slot pushing through, but by the
afternoon additional shortwave energy moving through the flow
aloft combined with residual low level moisture and west/northwest
upslope flow will allow for some scattered showers to develop,
mainly across northern portions of the area. With this loss of
insolational heating, any showers should dissipate though by the
late evening with clearing skies developing Saturday night as high
pressure edges into the region. Under the influence of the upper
low, temps through the period will be on the cool side of normal
for early July, with highs ranging only from the mid 60s to low
70s, and lows in the mid 40s to mid 50s.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 328 PM EDT Thursday...Long term period highlight will
feature another prolonged dry stretch along with temperatures
moderating back towards seasonal normals. Behind the departing
trough for the early part of the weekend, surface high pressure
will build into the region for Sunday with building heights aloft
going into the early to middle part of next week. The result will
be mainly dry conditions, partly sunny/clear skies and pleasant
humidity. Highs will generally range from the mid 70s to low 80s,
and lows mainly in the 50s mountains to low 60s valleys.
.AVIATION /00Z Friday THROUGH Tuesday/...
Through 00Z Saturday...VFR/high pressure with light terrain-
driven winds less than 10 knots expected through 15Z Friday.
After 15Z advancing cold front will trigger scattered to numerous
showers and thunderstorms across the region as winds trend
southerly 6-12 kts and occasionally gusty with sct/bkn VFR cigs
from 050-100 AGL developing. Some of the thunderstorms may become
strong to locally severe with turbulence, gusty winds and hail
possible along with brief MVFR/IFR. Timing of storms generally
from 18-00Z from west to east after which activity should
Outlook 00Z Saturday through Tuesday...
00Z Saturday through 03Z Saturday...lingering showers/storms, a
few strong to locally severe early will wane and exit east.
03Z Saturday through 12z Saturday...Areas of MVFR ceilings possible
(mainly SLK/MPV) with westerly wind shift following frontal passage
late Friday evening. Isold rain showers possible during Friday
night, diminishing toward daybreak Saturday.
12Z Saturday through Tuesday...Mainly VFR through the period. Broad
upper trough brings a chance of light rain showers across the
northern mountains and International border area during the daylight
hours Saturday. LIFR possible in fog MPV/SLK early Monday and
Tuesday A.M., mainly 06-11Z.
As of 140 PM Thursday...Will be monitoring the potential for
heavy downpours Friday afternoon and evening associated with the
anticipated widespread showers and embedded thunderstorms. Strong
QG dynamics (700-500mb vort axis moving SW to NE across the
region) and associated surface front will move into environment
across the North Country with MLCAPE values generally 500-1000
J/kg, and moderate PW axis of 1.3 to 1.5" during the mid afternoon
through early evening hours. The mid-level trough is progressive
in moderately strong swly flow, which may limit duration of
heavier downpours in most locations. However, some indication of
backbuilding potential of storms with MBE vectors NE at 5-10kts
per NAM model soundings across central/nrn VT. So, will need to
monitor for training cells as convective evolution occurs. Areas
such as Franklin and western parts of Clinton County in NY as well
as the northern VT counties of Orleans, Caledonia and Essex
Counties would be slightly more vulnerable to flash flooding,
given antecedent saturated soil conditions from rainfall past 2-3
days. Main stem river flooding is not currently expected.