Area forecast discussion
National Weather Service Burlington Vermont
101 am EDT Tuesday may 21 2013
Synopsis...
unsettled weather pattern is expected...as a frontal boundary
ambles about the North East....resulting in several rounds of
rain showers and thunderstorms into the middle of this week. High
pressure and drier conditions return Friday and continue into the
weekend...with cooler temperatures about 5 degrees below normal.
&&
Near term /until 8 am this morning/...
as of 1251 am EDT Tuesday...ongoing line of convective showers and
embedded thunderstorms vicinity of Lake Ontario is moving eastward into
a region of shortwave ridging...but is also being fed by moist
low-level southwesterly flow of 40-45 kts per ktyx VAD wind profile at
0445z. While it/S tough to pinpoint exact location...activity is
progressing eastward along stationary boundary with 850-700mb warm air advection expected
to increase eastward across northern New York into northwestern Vermont 06-12z time frame. NAM
forecast soundings show elevated instability developing eastward with
values up to 600 j/kg into the Champlain Valley 09-12z. Latest radar
reflectivity also indicates scattered cellular activity developing
near western St. Lawrence County...just in advance of the pre-
existing convective line.
Above factors warrant raising probability of precipitation to likely across northern New York into
western Vermont next several hours...with chance of thunderstorms mentioned across
northern New York and slight chance into western Vermont. Could see a quick quarter to
half inch of rainfall with some of the heavier activity next
couple hours. Areas of patchy fog may actually decrease overnight
as rain moves eastward. Temperatures will likely hover in the middle-upper
50s most sections through the remainder of the overnight hours.
&&
Short term /8 am this morning through Wednesday night/...
as of 355 PM EDT Monday...stalled frontal boundary remains over
the north country during the short term period and will be the
focus for periods of rain and possible thunderstorms through
Wednesday.
Rain showers spread eastward Tuesday morning with cloudy skies and
southerly winds. GFS being the outlier takes the boundary to our
south Tuesday afternoon...with most guidance keeping it over the north
country. 925mb temperatures depict the boundary over the area
well...with cooler temperatures over the nek Tuesday and most of the
area seeing 925mb temperatures in the low to middle teens. Clouds continue
over the area with rain showers and even lifted indices of -2 for
at least northern New York and southern half of Vermont. Some cape and temperature lapse
rates of 6-7 c/km could help trigger a few ts Tuesday afternoon.
Moisture continues to stream in to the north country with gefs
showing precipitable waters of 1 to 3 Standard deviations above normal
throughout the period.
Tuesday night...well depicted warm front lifting north as we
continue to be in the warm sector and 925mb temperatures increase to
upper teens...possibly low 20s on Wednesday. Surface low moves into
southeastern Ontario...resulting in SW flow...bringing in more
instability on Wednesday. Best chances for ts will be on
Wednesday as lifted indices of zero to -4 spread over the entire
north country. Temperature lapse rates greater than 7c/km will also move
into the area. Some showers and storms will linger into Wednesday
night as low level SW jet increases in strength at 30-40 kts.
Temperatures throughout the period will be above normal in the 70s
Tuesday and nearing 80 on Wednesday. Overnight lows will be mild
due to clouds...in the 50s and low 60s.
&&
Long term /Thursday through Monday/...
as of 425 PM EDT Monday...
A cold front with showers and thunderstorms on Thursday will usher
in cooler and mainly dry weather for the upcoming Memorial Day
weekend.
Confidence fairly high in the large-scale features as upper trough
passes slowly across the region. Some uncertainty in how the trough
evolves and how fast it moves out toward the end of the period.
On Thursday the cold front will move slowly southeast through the
area. Instability expected to be marginal with cape values around
500 j/kg or so and will depend upon cloud cover. With less cloud
cover values could climb near 1000 j/kg especially south and east
of btv. If the instability materializes and 0-6km bulk shear
values of 30-40 kts will have to watch for a few stronger storms.
Highs should be in the 70s with 850 temperatures around +12c.
Thursday night will feature a transition to much cooler temperatures with
850 temperatures falling to near 0c by 12z Friday. Could be some
lingering showers over night.
A cool northwest flow on Friday and Saturday with 850 temperatures around 0 will
keep high temperatures in the upper 50s to middle 60s with plenty of
cumulus clouds and even a chance of a shower during the afternoon
or evening hours especially in the mountains. Low temperatures
will be mainly 35 to 45.
Sunday and Monday should be dry as high pressure moves into the
northeast and temperature will begin to return to normal with
highs in the upper 60s to low 70s and lows in the 40s.
&&
Aviation /06z Tuesday through Saturday/...
through 00z Wednesday...low level moisture remains over the area
and this should lead to a trend from VFR ceilings and visibilities
to MVFR/IFR ceilings/visibilities between 04z and 14z. Rain
showers will move into southern Quebec province later tonight and
drop into northern New York and northern Vermont after 08z. The
threat for showers will continue throughout the morning and
afternoon hours on Tuesday. Winds will be variable under 10 knots.
Outlook 00z Wednesday through Saturday...
Tuesday PM...warm front brings MVFR showers with embedded thunderstorms with
brief IFR. Wednesday- Thursday...showers/thunderstorms with periods of MVFR
conditions. Thursday night into Fri/Sat...mainly VFR as dry northwesterly winds
develop.
&&
Btv watches/warnings/advisories...
Vermont...none.
New York...none.
&&
$$
Synopsis...kgm
near term...banacos
short term...kgm
long term...Sisson
aviation...evenson/Sisson
