Area Forecast Discussion
Issued by NWS Binghamton, NY

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FXUS61 KBGM 290545

Area Forecast Discussion
National Weather Service Binghamton NY
145 AM EDT Thu Sep 29 2016

A large, slow moving low pressure system will settle into the
Tennessee Valley tonight, then lift through the Northeast this
weekend. Expect overcast conditions with rain at times from
tonight through Saturday.


930 PM Update...

A large cut off low is in the process of moving south over the
state of Indiana. For much of the night our area has been in a
diffluent pattern on the east side of the low with any
precipitation weakening as it moved into our drier lower
atmosphere. Over the next few hours the upper level flow which has
been from the southwest, will slowly back toward due south.
Meanwhile an increasing plume of moisture continues to develop
over the Carolinas north through the Mid Atlantic. This plume of
moisture is already making its way into SE PA. You can already see
the impacts of this change in wind direction in the upper levels
with precip growing in coverage over southern PA. Of interest is
the movement here is now northward and not to the northeast.
Through the night strong 850 MB winds about 2 standard deviations
above normal over PA will help to increase the lift. In response precipitation
streaming out of the Mid Atlantic will continue to expand
northwest through the state of Pennsylvania. Our area will remain
on the northeast gradient getting the squeeze play with the
heaviest rains remaining to our southwest, with little rain over
our far northeast. With that in mind I trimmed back chances for
rain through 06Z given the radar trends. Still, toward daybreak
chances for rain will go up rapidly especially the farther south
and west you live in our forecast area. We posted a QPF graphic to
our website (message of the day at the top) and social media
(Twitter and Facebook) to give you a visual on what we are
thinking. The previous AFD is below.

A large, cutoff area of low pressure will settle into the Ohio and
Tennessee Valley regions tonight, then linger through Thursday. A
conveyor belt of moisture from the Atlantic Ocean will be drawn
into Pennsylvania and portions of New York tonight, allowing
showers to break out across our southern and western areas by
later this evening. Models are tending to agree in the overall
placement of this low, but there remains some uncertainty in the
details of exactly when and where the best forcing will develop,
and the most rain will fall. It`s a fairly safe bet to indicate
our highest probabilities for rainfall will extend from the
Wyoming Valley and Endless Mountains region of NEPA, into the
Central Southern Tier of NY. Less of a chance for steady rain up
through the Western Mohawk Valley. The main threat for excessive
rainfall is looking to be south of our region where anomalously
high amounts of moisture and strong low level wind forcing is
lining up on the lee slopes of the lower Allegheny Plateau. We
could see a few periods where rain comes down at a good clip
across NEPA and the Southern Tier, but at this time given the
antecedent dryness in the region, the threat for hazardous
rainfall problems looks minimal.

Temperatures, dewpoint and winds were developed from the
Superblend guidance. Sky cover was a bit more troublesome,
especially in the next few hours where marine layer was causing
trouble across the eastern counties. Low level RH fields seemed to
have a better handle on these clouds than anything.


Unsettled weather can be expected through this period as an upper
level low spins around in the Ohio Valley Thursday night through
Saturday before lifting northeast and finally moving off the east
coast sometime early next week. Occasional short-waves will rotate
around the upper low during the period but these will be very
difficult to time beyond a 12-24 hour lead-time. The first of
these waves appears to affect our area on Friday bringing an
enhanced chance of showers. Beyond Friday pops will be in the chc
category with short wave trough passages being impossible to time
at this lead time. These shower chances will continue into Monday
before diminishing as the upper low moves off to the east.
Persistent southeast flow with resultant precipitable water
values near to above 1.5 inches may result in localized heavy
rainfall Friday into the weekend with upslope locations such as
the Poconos or higher elevations of south central NY possibly most
favored for heavy rain.

Tweaked high temperatures down below the guidance blend by a few
degrees Friday through Sunday based on expected dense cloud cover
and showers... with highs barely reaching 60 areas where showers
are persistent. Otherwise went with the model guidance blend for
overnight lows into early next week.


The cutoff low is forecast to finally start to lift northward on
Saturday and eventually move out of the region by Monday evening.
However, until this low moved out of the region, we will continue to
have a chance for showers each day. Mostly cloudy skies will prevail
through the period along with temps only reaching the mid to upper
60s during the afternoon. High pressure will start to rebuild over
the region on Tuesday, breaking up the cloud coverage and allowing a
brief dry period to return.


Rain showers this morning are slowly developing across central NY
and NEPA. Expect showers to blossom over the next few hours as
and remain over the region through much of the morning. A blend of
MVFR and VFR showers are present this morning and as the morning
progresses expect flight conditions to deteriorate at all TAF
sites expect for KRME. Some IFR ceilings may develop near 12Z.
Showers with time will shift westward and all TAF sites are
expected to return to VFR by mid afternoon.

Winds will remain easterly around 8-15 knots through the period
with occasional gusts around 20 knots.


Thursday night-Monday...Occasional restrictions from showers
associated with upper level system in region.




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