Area Forecast Discussion
Issued by NWS Burlington, VT

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FXUS61 KBTV 291758

Area Forecast Discussion
National Weather Service Burlington VT
158 PM EDT Mon May 29 2017

Moist low-level air mass across Pennsylvania and New York
associated with a mid-level trough will lift northward into our
region later this morning into this afternoon. Widespread
showers will develop first across northern New York during the
mid to late morning hours, and then across Vermont late this
morning into this afternoon. A quarter to half inch of rain is
generally expected, with the highest amounts across the northern
Adirondacks and St. Lawrence Valley of New York. Overcast skies
and showers will keep temperatures in the upper 50s to mid 60s
today. The showers end by Monday evening. However, another
round of showers and some thunderstorms will move across the
area on Tuesday. A broad upper level low across Ontario and
Quebec will maintain temperatures near to slightly below
seasonal levels as we head into early June, along with daily
chances for shower activity.


As of 158 PM EDT Monday...Widespread rain continues across the
area early this afternoon...but noticeable back edge exists
across central New York and is moving eastward. Going forecast
has this handled well and no changes needed at this time.

Previous Discussion...
Relatively mild early this morning with combination of
increasing mid-level cloudiness and increasing S-SE gradient
flow keeping PBL well-mixed. Early AM temperatures generally in
the 55-63F range, highest in the Champlain and St. Lawrence
Valley areas. Have made just minor adjustments with the sunrise
update, mainly to bring in higher PoPs a bit earlier with
leading edge of rainfall across St. Lawrence County at 1130Z.

Rich low-level moisture lurks not far away. RAP-based SPC
Mesoanalysis shows PW values of 1.4" to 1.5" across central/wrn
NY and PA, collocated with sfc-700mb trough extending from sern
Ontario across srn NY/PA. As shortwave ridging across nrn New
England moves away this morning, all guidance is consistent in
lifting trough and associated moisture/WAA nnewd into the North
Country. Should see developing rain showers across nrn NY zones
12-15Z, and eventually across VT 15-18Z. Axis of precipitation
tied to the trough axis will shift newd thru the region
relatively quickly - by 21Z rainfall should end in nrn NY and by
00z should lift out of the Northeast Kingdom of VT. Overall,
looking for a quarter to half inch of rainfall falling over
3-6hr period, with the highest amts likely across nrn NY.
Temperatures may fall several degrees this afternoon with onset
of rainfall, with aftn readings mostly in the 50s. Gradient flow
does increase in advance of the rainfall this morning, and may
see a few gusts 20-30 mph across nrn NY and the Champlain Valley
until the onset of steadier rainfall early this aftn.

Relatively quiet conditions expected tonight, with variably
cloudy conditions and redevelopment of south winds 10-15 mph.
This should keep overnight temps from falling very much, with
lows mostly in the mid 50s in the Champlain and St. Lawrence
Valley areas, and upr 40s to lower 50s elsewhere where some
decoupling is possible (especially east of the Green Mtns).

Tuesday will feature deep-layer swly flow across the North
Country, with an embedded mid-level vort max shifting newd from
wrn NY into our region coincident with peak afternoon heating.
Low 50s dewpoints will mitigate overall surface based
instability, with SBCAPE values expected to remain below 1000
j/kg. That said, combination of synoptic forcing and sfc-6km
bulk shear of 40-50kts should result in developing aftn convective
showers and a few embedded thunderstorms, which may exhibit
some organization. Can`t rule out a strong tstm or two, with
brief heavy downpours and gusty winds/lightning, but activity
should generally remain below severe limits owing to modest
instability. Will continue to monitor. Highs on Tuesday mainly
in the upr 60s to lower 70s. May again see some gusty winds for
a time on Tuesday, especially in the St. Lawrence Valley with
gusts to 30 mph possible with valley channeled flow.


As of 351 AM EDT Monday...Tuesday night should still see some
activity east of Lake Champlain as an upper level shortwave will
be moving through the North Country. There will be some
marginal diurnal heating left over with some modest instability
so there will be a slight chance into the evening for some
rumbles of thunder, however as night falls expect the showers
and any potential of thunder to diminish. None of the storms
are expected to be severe although they could produce some gusty
winds and locally moderate rainfall. There really isn`t much of
a thermal gradient with the wind shift as the shortwave swings
through, so temps overnight will only fall to the mid 50s.
There is some potential for some fog development just before day
break on Wednesday as the winds should be fairly light behind
the precip and with dewpoints in the low 50s we could see at few
patches of some light fog. Confidence isn`t really there yet
especially with partly to mostly cloudy skies so I haven`t
included any mention in the forecast.

As we move into Wednesday afternoon another round of showers
can be expected as another shortwave rounds the bottom of a
persistent upper level low. Latest GFS and NAM continue to show
modest surface instability on order of 500-1000 J/kg with some
0-6km shear in the 30-40kts range. Nothing to write home about
but its enough to warrant the mention of chance thunder in the
afternoon and early evening hours on Wednesday. Again none of
these storms are anticipated to become severe but they could
produce some 30+ mph winds with some locally moderate rainfall.

The potential bigger item to note is that the 850mb jet axis
will be oriented from southwest to northeast right up the Saint
Lawrence valley and with decent mixing we could see 25-30kt
gusts locally in the Saint Lawrence. Elsewhere there really
isn`t much threat in the way of synoptically driven winds.

Temps on Wednesday should warm into the upper 60s to low 70s
with 925mb temps warming to 15C-16C by 21z. Then overnight
there`s a slightly stronger thermal gradient as the Wednesday
shortwave swings through. So we should cool Wednesday night into
the upper 40s to low 50s putting us near normal for the first
day of June.


As of 351 AM EDT Monday...The extended will be dominated by an
upper level low that is blocked by a strong northern Atlantic
low pressure system. So we`ll see several rounds of showers as
shortwaves round the parent upper level low to end the weekend.
Showery conditions will be the theme as the combination of
relatively steep mid- level lapse rates and surface heating will
result in shallow instability and shower development.

The trends in the latest guidance point to potentially dry days
on Thursday early Friday as we sit in between upper level
shortwaves and Thursday looks to potentially be dry in- between
shortwave troughs. Temps during the period look to be very
seasonal, with daytime highs in the mid 60s to low 70s, and
overnight lows in the mid 40s to low 50s.


Through 18Z Tuesday....Despite widespread rain exists across the
entire area this afternoon ceilings and visibilities remain in
the MVFR and VFR categories. Noticeable back edge to the
precipitation exists across central New York and thus looking at
precipitation coming to an end by 00z at all locations. Still
looking at MVFR and VFR ceilings after 00z and for the remainder
of the period. Winds aloft will continue overnight and this
should limit fog potential...but plenty of low level moisture
remains for some low clouds and fog to develop at KSLK and KMPV.
There may be some showers across northern New York and western
Vermont after 12z...but majority of any precipitation will come
after 18z. Winds will remain from a general southerly direction
through the period at speeds in the 5 to 15 knot range with some
gusts to 20 knots.


Tuesday Night: VFR. Chance SHRA...Slight Chance TSRA.
Wednesday: VFR. Breezy. Chance SHRA...Chance TSRA.
Wednesday Night: VFR. Chance SHRA...Slight Chance TSRA.
Thursday: VFR. Slight Chance SHRA.
Thursday Night: VFR. Slight Chance SHRA.
Friday: VFR. Chance SHRA.
Friday Night: VFR/MVFR. Chance SHRA.
Saturday: VFR. Slight Chance SHRA.


Lake Wind Advisory continues in effect. South winds will be in
the 15-25 knot range today. These winds will create rather
choppy conditions and the strongest winds (around 25kts) are
expected during the midday hours. Should see south winds
continuing in the 15-25 knot range right into Tuesday.




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