Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Burlington Vermont
733 am EDT Sat Aug 30 2014
warmer and more humid conditions will develop across the north
country today as surface high pressure shifts east of New England
and winds increase from the south and southwest. An upper level
disturbance will approach from the Great Lakes late tonight into
Sunday...resulting in increasing cloud cover and widespread
showers and embedded thunderstorms during the day Sunday.
Conditions are favorable for brief heavy downpours...especially
with any thunderstorm activity Sunday. Drier weather returns on
Monday...followed by scattered showers ahead of an approaching
cold front for Tuesday. Temperatures are expected to remain above
normal over the next 5 to 7 days...with Valley High temperatures
likely reaching the middle 80s on Monday and Tuesday.
Near term /through tonight/...
as of 731 am EDT Saturday...south to southwesterly low-level flow
will increase today across the north country...between surface high
pressure departing east of New England and weak surface low moving eastward
through the central Great Lakes. The southerly return flow will allow
humidity to increase slightly...with surface dew points reaching the
middle to upper 50s by this afternoon. Also...850mb thermal ridge
develops into the region from SW-NE...with temperature values of +15 to
+16c by 00z this evening. Already seeing some cirrus clouds within
anticyclonic flow/upper ridging in place...so will see periods of
filtered sunshine throughout the day...especially northern zones.
Looking at highs reaching the upper 70s to lower 80s...highest in
the Champlain and St. Lawrence valleys. S-SW winds generally 10-15
miles per hour...but locally 20-25 miles per hour in gusts (and sustained 15-25 kts over
Lake Champlain...where a lake Wind Advisory has been posted for
today). With middle-level ridging remaining in place through the day and
not much evidence for low- level convergence...it appears it will
remain dry today into the first half of tonight. Have kept probability of precipitation
below 15 percent.
Middle-level height falls commence tonight...especially after
midnight as upper ridge weakens and middle-level shortwave trough
continues eastward across the Great Lakes. Skies should become mostly
cloudy from west to east overnight...with continued S-SW winds.
This will help kept temperatures up into the low-middle 60s for most
sections. Likewise...continued low-level moisture advection will
allow dew points to climb into the low 60s...and locally into the
middle 60s for the St. Lawrence Valley region. May see a few showers develop
after midnight...generally across northern New York with mainly dry
conditions in Vermont. Enough wind/increase clouds should preclude fog
Short term /Sunday through Monday/...
as of 351 am EDT Saturday...Sunday will be an active day as middle-
level trough and associated vorticity maximum shears eastward from southeastern Ontario
across northern New York and Vermont by early Sunday evening. The persistent S-SW
flow in advance of this middle-level feature results in precipitable water values of
1.8-2" across the north country. While clouds will limit the
extent of instability...do anticipate some SBCAPE of 500-1000
j/kg. Combined with approaching middle-level upward vertical velocity...will yield
widespread showers with some embedded thunderstorms across much of
the north country. Best potential for thunderstorms will be during
the afternoon hours with best potl for instability. Given high
freezing levels and precipitable water values...continued with idea with some
locally heavy downpours will be possible with any thunderstorms.
Westerly surface-6km bulk shear only 20-25 kts...and combined with weak
lapse rates/instability should preclude any severe threat. Storms
should also be moving eastward enough that do not anticipate any flood
threat. That said...a few localized rainfall amts of 1+" can/T be
ruled out. Probability of precipitation generally 60-80 percent...highest across
central/eastern Vermont during Sunday afternoon. High temperatures generally 78-81f
across the region.
System shears to our east Sunday evening with generally flat sea-
level pressure field Sunday night. With some partial
clearing...could see some locally dense fog (especially areas
getting the more significant rainfall sunday). Lows generally in
the low-middle 60s with light winds.
Monday appears generally quiet and continued warm/humid. Highs
will reach the low-middle 80s in valley sections under partly to
mostly sunny skies. Not much forcing for ascent with weak
shortwave ridge...so most areas should remain dry for Labor Day.
Winds light south to SW at 5-10 miles per hour.
Long term /Monday night through Friday/...
as of 351 am EDT Saturday...main concern for weather in the extended
forecast period...Monday night through Friday...will be Tuesday
and Tuesday night. Upper level trough and its associated cold
front will be moving into the area during the afternoon and
evening hours. Ahead of the front...above normal temperatures are
expected with highs in the 80s and combined with increasing dew
points...sufficient instability will develop over the area ahead
of the front. Deep layer shear will also be increasing over this
area of developing instability. All of this suggests the potential
for thunderstorms...some of which could be strong or severe. Thus
will have to keep an eye on this system. Will continue the idea in
the forecast for showers and thunderstorms Tuesday and Tuesday
night. Once the front exits the area late Tuesday night...drier
weather moves in for Wednesday...Thursday... and most of Friday.
High temperatures Wednesday through Friday will be right around
Aviation /12z Saturday through Wednesday/...
through 12z Sunday...overall looking at VFR conditions through the
period. Mainly middle and high level clouds through the day
today...then ceilings begin to lower tonight with broken to
overcast ceilings around 5000 feet by 06z. There will also be some
light showers moving from west to east between 06z and 12z...but
visibilities will remain unrestricted. Light winds early this
morning will begin to increase from the south after 13z or 14z with
gusts in the 15 to 20 knot range through about 00z.
Outlook 12z Sunday through Wednesday...
12z Sunday Onward...mainly VFR, though MVFR/brief IFR in scattered
showers and thunderstorms that will be most numerous Sunday and
perhaps again late Tuesday.
as of 418 am EDT Saturday...south winds will increase sharply on
Lake Champlain toward daybreak as the pressure gradient increases
between high pressure departing east of New England...and a
developing low pressure system across the central Great Lakes.
Winds at 4 am had already reached 18 kts at Colchester Reef.
During the daylight hours...south winds generally 20-25
knots...helping to build waves to 2-4 feet by this afternoon. A
lake Wind Advisory has been posted.
Saturday night winds will increase slightly higher as Champlain
Valley funneling and low-level nocturnal low level jet set up so
winds may nudge a bit higher 20 to just shy of 30 knots overnight.
A few waves over 4 feet may occur on the north half of the Open
Lake. There will be an increasing chance of showers after
midnight...and especially toward daybreak.
Sunday south winds will taper off to 10 to 20 knots and waves will
subside to 1 to 3 feet. Looking for widespread showers and a chance