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fxus61 kbgm 302006 
afdbgm

Area forecast discussion
National Weather Service Binghamton New York
406 PM EDT sun Apr 30 2017

Synopsis...
an isolated shower will be possible through tonight, but most
of the time it will be dry. Warm unstable air will surge into
the area Monday, setting the stage for thunderstorms Monday
afternoon through evening. Some of those storms could be severe
with damaging winds and locally heavy rainfall. Cooler yet
still unsettled conditions are expected for midweek.

&&

Near term /until 6 am Monday morning/...
345 PM update...
main concern is for potential severe weather Monday afternoon
through evening; that is further detailed in the short term
portion of this discussion.

In the meantime, mostly dry conditions are expected through
tonight. Pervasive clouds are finally starting to breaking up as
warm sector of incoming system starts to make its way in.
Instability is also cropping in up western PA-New York with widely
scattered diurnally driven showers and non-severe thunderstorms.
A few of these may reach to central twin tiers this evening and
along New York thruway overnight, but they are not of much concern.
Also, moist upsloping southeast wind against the Catskills-
Poconos could result in spotty light showers and drizzle as well
as patchy fog tonight. It will be mild with lows ranging from
upper 40s to upper 50s.

&&

Short term /6 am Monday morning through Monday night/...
4 PM update...
we have increasing concern for severe weather potential for
Monday afternoon through evening. It was never a question of
shear - there is plenty of that - but of instability. Models
have come together in allowing for good heating ahead of pre-
frontal trough followed by eventual cold front Monday night.
Widespread 70s, with some spots to near 80, appears likely for
highs Monday. This along with dewpoints surging to around 60 is
more than adequate to generate the required instability that is
necessary for thunderstorm development. Model soundings indicate
that western New York-PA, where initial convection will fire, should
have at least several hundred j/kg convective available
potential energy and perhaps approaching 1000 j/kg.

The NAM model puts more focus on the cold front itself, which is
a known bias in situations such as this. Other model guidance,
which is preferred, allows pre-frontal trough to generate the
bigger focus on convection. Timing of main concern appears to
be roughly 4pm west to 10pm east. However, front itself will
still be capable of producing its own convection overnight which
could be a problem in terms of locally heavy rainfall-possible
flash flooding.

Lapse rates will not be extremely steep, but other indicators
are worrisome. This includes 0-1km helicity in the hundreds,
0-1km shear well over 20 knots, 0-3km plus 0-6km shear values
around 50 knots or so. There will also be good upper forcing via
12 hour 500mb height falls greater than 100 meters. We entered in
expected values into our local severe weather checklist tool
which compares parameters to analogs of past events. The tool
returns analogs with many damaging wind reports, and a couple
tornadic events as well. This all supports the Storm Prediction
Center upgrading our severe weather risk values in the day 2
convective outlook for Monday. Storm Mode is likely to evolve
into a damaging wind threat including possible Bow echoes; but
in the initial stages, there could be discrete supercells and
tornadoes are not out of the question. The key will be how long
it takes to evolve to primarily damaging wind.

Finally, with precipitable water values getting around an inch-
and-a-half and soils still very wet, flash flooding potential
cannot be discounted. Storms and lines will be very
progressive, but with both pre-frontal trough and then actual
cold front in play, as well as possible individual cells popping
up ahead of those features, localized areas may get repeated
batches of heavy rain.

Late Monday night, behind the front much cooler air will rapidly
advect in with lows in the lower to mid 50s. Scattered showers
will also persist overnight, behind the frontal line of
convection that passes through in the evening.

&&

Long term /Tuesday through Sunday/...
230 PM update...

Continued unsettled pattern with temperatures falling to closer
to average or a little below. An upper level trough will be
over the area to start then lift slightly before a reinforcing
shot of cold air aloft Friday. Fortunately fairly moist so
little clearing so a freeze looks unlikely attm. Tuesday to
Wednesday showers with cold northwest flow on back side of
large storm. Wednesday night a brief break under high pressure.

Models now in close with a soaking rain of at least an inch
Thursday to Friday. Moisture streams northeast ahead of another
strong stacked low. This will bring rain for Thursday and
Friday before more showers on Saturday as the trough lifts
slowly northeast into far eastern Canada. Difference between
this storm and Monday/Monday night is the speed. Thursday to
Friday much slowly and a better chance of higher rainfall. Will
need to watch closely for flooding.

Models diverge on the weekend and whether a weak storm makes it
here or area stays dry Sunday. Put in low chance pops.

Highs on the cool side for early may with highs mostly in the
50s and lows in the 40s. Coldest night Wednesday night with the
brief high pressure. Some locations will fall into the 30s but
frost uncertain still.

&&

Aviation /20z Sunday through Friday/...
mainly VFR conditions are expected for the afternoon through
early evening. However, a return to MVFR ceilings is likely
for most terminals overnight as conditions stabilize and
moisture collects below the inversion; less likely for ksyr and
thus not in that taf. Fuel alternates possible for kbgm-kavp. A
strengthening south-southwest low level jet 35-40 knots will also introduce
low level wind shear to most terminals so that is included in
all tafs except kbgm at this time. See individual tafs for
specifics on timing of both MVFR cigs and low level wind shear. Surface winds
will be generally east-southeast 6-9 knots, increasing slightly while
veering more southerly into Monday.

Outlook...

Monday afternoon into Monday night...restrictions likely as
thunderstorms sweep west to east across the region.

Tuesday through Wednesday night...mainly VFR but a chance of
showers and associated restrictions at times.

Thursday through Friday...restrictions likely with rain from
slow-moving low pressure system.

&&

Bgm watches/warnings/advisories...
PA...none.
New York...none.

&&

$$

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