Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 300829

Area Forecast Discussion
National Weather Service Burlington VT
429 AM EDT Sun Apr 30 2017

Today will start off cooler and near normal for late April.
Persistent, cool northernly flow along with increasing clouds
ahead of a warm front will keep temperatures in the 40s to 50s
today. A large strengthening low pressure system over the Ohio
valley region will lift a warm front through New England
bringing another chance for rain late today into this evening.
Unsettled weather will continue through the mid week, followed
by the potential for another low pressure system to affect the
region late in the week.


As of 429 AM EDT Sunday...Ridging aloft and at the surface will
start out the day before the ridge axis shifts east of the
North Country and a warm front moves over the area. This will
result in warming mainly in the afternoon hours with increased
clouds and potential for showery activity. Models continue to
differ on placement of the warm front...affecting how widespread
rain showers will be over the North Country today. Expect best
chances for showers will start in the late morning/early
afternoon across portions of Northern New York. As the warm
front lifts north, expect showers to affect the St Lawrence
Valley, Adirondacks, around the international border, and the
higher terrain. The warm front will lift north of the
international border during the early evening, followed by an
embedded vort that looks to produce more showers Sunday night
reaching further south into the Adirondacks, lower Champlain
Valley, central Green Mountains and areas northward. Also a low
level jet of 20-30kts represented on the models at 925mb
overnight. This will aid in the WAA and non-diurnal temperature
trend, especially in the Champlain valley. Precip associated
with the warm front looks to lift northward Monday morning ahead
of cold front to our west. Monday most of the North Country
will firmly be in the warm sector with some breaks in clouds for
the Champlain Valley, eastern Adirondacks and south central
Vermont. However, NE winds channeling down the St Lawrence
Valley will keep temperatures cooler and more persistent clouds.
Eastern Vermont and the Northeast Kingdom will likely see a
similar situation with cooler temperatures and more stubborn
cloud cover.

The frontal boundary that is associated with closed surface low
around the Great Lakes Region on Monday will near the St
Lawrence Valley Monday afternoon, bringing showers and possibly
thunderstorms to the region as we head into Monday night.
Stronger low level jet looks to enter the southern St Lawrence
Valley towards the end of the period, providing potential for
gusty winds.

Temperatures throughout the period will start cool with near
normal temperatures this morning (low around 40 at BTV), will be
slow to warm today as colder northerly flow is in place and the
aforementioned warm front will be slow to lift into the North
Country and bring with it warming trend. Tonight, temperatures
look to be 5-10 degrees warmer that this morning as the warm
front lifts north and WAA settles in over the North Country.
Monday`s max temperatures will vary widely. Areas remaining in
cooler NE flow (NEK and SLV) will reach 50s to low 60s, while
CPV and western slopes of the ADKS could see temperatures in the
upper 60s into the 70s.


As of 322 AM EDT Sunday...Very active period of weather
anticipated with sharp cold front and strong dynamics will
interact with weak low level instability parameters to produce a
fine line of low top convection on Monday Night. Latest
guidance continues to show surface based capes up to 500
j/kg...especially northern NY between 00z and 03z Tues...along
with strong low to mid level wind fields...resulting in 0 to 6
km shear values of 40 to 50 knots. Based on magnitude of low
level winds and height falls associated with approaching
mid/upper level trof...have bumped pops to 90 to 100% on Monday
night...with a line of showers with embedded convective elements
expected. A few localized wind gusts and brief heavy downpours
are likely...especially as pws surge between 1.00 and 1.50 ahead
of boundary. Qpf will range between 0.25 to 0.75...with
isolated amounts near 1.0 across the dacks/slv on Monday
night...where dynamics and instability parameters are the
strongest. Additional showers are likely on Tuesday associated
with mid/upper level trof approaching and embedded 5h vorts.
Thinking mid level dry slot will be impacting our cwa around 12z
Tuesday...but deeper moisture redevelops as mid/upper level
trof approaches by 18z Tuesday...with precip becoming terrain
focused on southwest flow. Have mention likely pops in the
mountains with chance in the valleys for Tuesday with an
additional one to three tenths of qpf possible...especially high
peaks of the dacks. 925mb to 850mb winds of 30 to 40 some localized gusts up to 30 mph in the
southwest to northeast aligned valleys like the slv on Tuesday.
Some downslope shadowing is likely in the cpv with strong
southwest flow. Temps under modest low level caa on Tuesday will
generally range from the 40s mountains to near 60f warmer
valleys. Upslope terrain focused showers continue into tuesday
night with some mix of snow likely above 2000 feet as progged
850 and 925mb are at or below 0c. Would not be surprised several
inches of snow accumulates on summits by 12z Weds...given
thermal 850mb thermal profiles between -2c and
-5c with favorable upslope precip prevailing.


As of 322 AM EDT Sunday...Little change from previous couple of
days with development of full latitude trof expected across the
eastern conus and several periods of moderate precipitation
expected late Thursday into next weekend. Some lingering upslope
precip will end by Weds afternoon with weak high pres building
into our cwa on Weds into Thursday. This will keep forecast area
dry with near normal temps.

Models still have some disagreement on phasing of northern/southern
stream systems and overall magnitude of trof and associated surface
low pres track. Either solution supports a period of moderate mid
level waa rain on Friday with strong ulvl divergence pattern
associated with dual jet couplet. Have bumped pops into the high
likely to low cat range with widespread qpf anticipated. Both the
gfs/ecmwf show cold pocket of progged 850mb temps <0c as precip would anticipated some wet snow/sleet on the summits
Thursday Night into Friday Morning. Initial surge of moisture should
be north of our cwa by Friday afternoon with well established dry
slot developing from southwest to northeast. This will result in
more showery precip Friday Night into Saturday...before additional
steadier precip redevelops on Sat Night into Sunday associated
backside deformation. Latest trends support enough cold air
advection into the system on backside northwest winds for a mix of
rain/snow in the mountains with some accumulating snowfall possible
above 2000 feet. As large scale omega block develops across the
conus...look for a prolonged period of upslope precip to prevail
Saturday Night into early next week. Have mention high chance to low
likely pops. As progged 850mb temps drop below 0c by 00z
Sunday...expect some accumulating snowfall for the northern dacks
into the central/northern Greens on Saturday Night into Sunday.
Several inches is likely above 2000 feet. Temps near normal for
Weds/ to below normal for Friday into the weekend
with highs mainly 30s summits to l/m 50s valleys...which maybe
generous for Sunday given progged 850mb temps near -4c. Overnight
lows will remain in the 30s to m/u 40s because of clouds/precip.


Through 06Z Monday...VFR conditions persist with N-NW winds
generally 10 kts or less through sunrise. Winds become more
northerly at 6-10kts during the day Sunday with increasing
clouds ahead of a warm front associated with significant low
pressure system over the central CONUS. There may be some light
showers moving into the Saint Lawrence Valley around 15Z,
reaching the Champlain Valley after 20Z...but visibilities are
expected to remain in the VFR category. Another bout of rain
showers possible Sunday night, mainly after 04Z.


Monday: VFR/MVFR. Breezy. Chance SHRA...TSRA.
Monday Night: MVFR. Likely SHRA...TSRA.
Tuesday: VFR. Breezy. Likely SHRA.
Tuesday Night: VFR. Chance SHRA.
Wednesday: VFR/MVFR. Chance SHRA.
Wednesday Night: VFR. Slight Chance SHRA.
Thursday: VFR. Chance SHRA.




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