Area Forecast Discussion
Issued by NWS Binghamton, NY

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FXUS61 KBGM 220823
AFDBGM

Area Forecast Discussion
National Weather Service Binghamton NY
423 AM EDT Sat Jul 22 2017

.SYNOPSIS...
A chance of thunderstorms will visit mainly Northeast
Pennsylvania late today into tonight. Some showers and isolated
thunder could edge into Central New York. After quiet conditions
late tonight to midday Sunday, there will be a more areawide
likelihood of showers and thunder late Sunday through Monday.
Dry high pressure is expected Tuesday and Wednesday.
&&

.NEAR TERM /THROUGH SUNDAY/...
415 AM Update...
There is a limited risk for thunderstorms with locally heavy
rainfall and gusty winds late today through this evening, but
the focus will be mainly south of our area, in Central to
Southern Pennsylvania. Then Sunday afternoon, while shower and
thunder chances will begin to increase areawide, most of it
will hold off until Sunday night.

Models have continued their recent shift in placing instability
further south compared to prior thinking. This is a welcome
development, in that while not completely removing the threat,
this trend significantly diminishes it in size and scope.
Mesoscale convective complexes have erupted in the Midwest,
around Chicago to Indianapolis. The frontal boundary ahead of it
will sink further south than previous expectations. The
upstream convection and associated shortwave aloft will roughly
follow along 500mb height lines, almost due east yet slightly
south. Deep layer shear will definitely be present especially
the 3-6 km layer which along with dry air in the lowest levels
will promote gusty winds in the storms that carry across, but
the stalled out stationary or warm front ahead of the wave of
low pressure will be positioned from northwest to east-central
Pennsylvania. So for our area, Northeast Pennsylvania and
specifically the Wyoming Valley/Scranton /Wilkes- Barre/Poconos
areas will have this risk for thunderstorms with strong gusty
winds roughly between 5PM-11PM.

The air mass just to our south will be very moisture-rich, with
precipitable values around 2 inches. Though the surface front
will be quite far south, late today at 850mb a low level jet
will attempt to force moisture over that surface front.
Convection will tend to move very fast yet could also contain
brief heavy rainfall rates in Northeast PA and especially
Wyoming Valley area. Showers and isolated thunder, harnessing
some instability aloft, may encroach into the Southern Finger
Lakes-Southern Tier-Catskills late today and especially this
evening. However, the risk for excessive rainfall now appears
minimal compared to further south.

Late tonight through midday Sunday, a fairly quiet period is
foreseen between waves. However, frontal boundary will begin to
drift northward with time Sunday afternoon. Models significantly
differ on how long it takes instability and moisture to
materialize in the form of convection. The GFS model actually
poses the most problematic solution in terms of severe weather
potential, due to quicker northward push of warm sector ahead of
the next low pressure wave, and a sheared wind profile that is
common with shallow warm fronts. However, most other model
guidance has trended less significant with the threat Sunday
especially during the day. Regardless, the better chance for
showers and thunder appear to be as we head into Sunday night.
&&

.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
Unsettled and potentially stormy this period as a fairly sharp
upper level trough and associated surface low move through the
area.

To begin the period Sunday evening, progressive upper trough will
be diving S/E toward the area with most models indicating
surface low positioned over the Finger Lakes. This would place
western parts of the CWA in the warm sector where showers and
storms will likely be ongoing. The notable exception is the NAM
which is much slower and weaker with this system and keeps more
stable air over the area due to stronger ridging from the east.
So there is uncertainty with this forecast but we generally
leaned toward a non NAM compromise. If this solution (non-NAM)
is what verifies concern is that there could be a fair amount of
instability in the warm sector over the western southern tier
into the Finger Lakes with ML CAPES possibly exceeding 1000
j/kg. Deep layer shear also looks to be in the 30-40 knot range
with forced deep layer ascent due to good jet dynamics. Finally,
there also looks to be good low level turning of the winds.
These factors all indicate the potential for severe weather and
also the possibility of Flash Flooding as there will be a deep
moist layer with PWATs near 2 inches. Again, a lot of
uncertainty at this point as it`s possible the best severe
weather threat may be just west of our forecast area more
through western NY/PA. However we`ll continue to mention threat
in HWO. As the system moves across the area Monday night, best
chance for heavy showers/storms and severe weather would be in
the evening with the warm sector getting shunted off to the east
overnight.

Monday...the initial slug of moisture will have moved off to the
east however a surface trough looks to hang back across the
area with lift also being supported by the upper trough axis
which will swing through during the day. This will keep showery
weather over the area with additional thunderstorms also
possible...especially in the afternoon. Temperatures will be
cooler with highs mainly in the 70s.

Monday night...system will be moving away but one final
shortwave will move through which will keep the chance of some
showers going, especially in the east. However do expect that
showers will become lighter and more scattered to isolated with
time. Also, cooler air moving in behind the system will result
in lows dipping into the mid to upper 50s so a more comfortable
night compared to many recently.
&&


.LONG TERM /TUESDAY THROUGH FRIDAY/...
The area looks to see another respite from active weather
Tuesday through Wednesday as high pressure moves in. For Tuesday
there could still be a couple isolated lingering showers mainly
east of I-81 but otherwise expect these days to be dry under a
mix of sun and clouds. Temperatures will be on the cooler side
with highs in the 70s along with comfortable humidity levels.
Beyond this time, the next front looks to move south through the
area Wednesday night into Thursday bringing another round of
showers and thunderstorms. Seasonably cool conditions look to
then follow for the end of next week with the chance of
lingering scattered showers as models indicate the area will be
in cyclonic flow aloft under the influence of a large upper
trough over Quebec.
&&

.AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
Fairly quiet early this morning, though with a typical valley
fog concern for KELM and KAVP. While current conditions will
promote some formation, the tricky part is that thunderstorms
way upstream of the area are causing a shield of high thin
clouds well out ahead of them, and those clouds will spread
over the area towards dawn. The affect will be to hold back fog
development. KELM-KAVP should probably still reach IFR VIS for a
time, but may not get any worse than that. Other than the brief
valley fog for a couple terminals before dawn, generally VFR
conditions are expected today. After 22Z, some showers and
thunderstorms will skim a part of the area. There is uncertainty
as to where, but KAVP stands the best chance of at least
showers if not thunder during the 00Z-06Z Sunday period. Thunder
and restrictions are not impossible further north, such as
KELM-KBGM, but it will have a much tougher time reaching there
thus it is not in TAF at this time. Winds will be generally
variable less than 5 knots through the period.

Outlook...

Sunday through Monday night...Periodic restrictions in showers-
thunderstorms, especially late Sunday into Monday.

Tuesday through Wednesday...VFR.

&&

.BGM WATCHES/WARNINGS/ADVISORIES...
PA...None.
NY...None.

&&

$$
SYNOPSIS...MDP
NEAR TERM...MDP
SHORT TERM...PCF
LONG TERM...PCF
AVIATION...MDP



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