Area Forecast Discussion
Issued by NWS Binghamton, NY

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FXUS61 KBGM 121252

Area Forecast Discussion
National Weather Service Binghamton NY
852 AM EDT Mon Apr 12 2021

A slow moving area of low pressure over northwestern Ohio will
move into central Pennsylvania this evening, and head off the
Mid Atlantic coast by Tuesday morning. This system will continue
to bring plenty of cloud cover and bands of showers to the
region through this evening. Spotty showers will mainly affect
areas west of I-81 Tuesday afternoon, but there will be a
noticeable decrease in shower coverage through Wednesday
afternoon, with some sunshine returning as well. Another upper
level storm system will approach from the west Wednesday night,
bringing unsettled weather back to the area through the weekend.


850 am Update...

The main update was the PoPs. A band of showers is retreating
northwestward over Yates and Seneca Counties, so kept PoPs
fairly high there but decreased them everywhere else. For the
next few hours, followed closely with the HRRR as other guidance
seemed to have too many showers over the area this morning.
Another band is expected to form over the Finger Lakes region
later this morning, so began the transition of increasing PoPs
once again after this upcoming hour. Also touched up temps and
winds for the next few hours based on the latest obs.

...Previous Discussion...

The rain band over eastern PA has mostly dissipated this
morning as it pivoted into the Wyoming Valley and Poconos, as
upper level forcing weakened rapidly. Showers recently have been
struggling to redevelop in a band north of a Cortland- Norwich
to Walton line, but the steadiest precip has been just north and
east of the CWA in a band associated with a mid-level
deformation zone.

High res models all indicate precip bands will redevelop by
late morning and persist through the afternoon as additional
vort lobes pivot into the area from the southwest. The most
persistently favored area looks to along an arc extending from
the Catskills into the northern Finger Lakes, near or just
north of Ithaca and Binghamton. Elsewhere, off and on showers
and sprinkles will be the rule of the day, along with cooler
temps. It`s difficult to pinpoint any place being more favored
for showers than any other outside the aforementioned band, and
there will be some places that stay relatively dry (rainfall-
wise) today. Broadly speaking, western parts of the CWA should
see an uptick in shower coverage late in the afternoon as the
upper low itself approaches western and central PA.

As the low passes south of the CWA, showers will increase in
the evening, then diminish as upper level forcing diminishes
quickly in the wake of the low. Drier low level air over New
England will also work in from the east overnight and Tuesday.
Most areas will even break out of the clouds on Tuesday,
especially east of I-81. A few showers may return to the Finger
Lakes late in the day.


430 AM Update...
This period starts off rather quiet Tuesday night and into the
first portion of the day on Wednesday, as our area will be
under the influence of upper level ridging. A weak warm front
translates across the area from west to east Tuesday evening
which could bring an isolated shower or sprinkle to CNY. Should
be mainly dry Wednesday morning with increasing clouds as an
expansive, slow moving upper level low begins to approach from
the Central Great Lakes region. Southwest flow increases through
the day, with increasing moisture advection. The latest model
guidance is trending slower with this next system...with that
said, still did leave in a low chance for a few rain showers
later Wednesday afternoon, mainly from the Twin Tiers south into
NE PA. However, at this time it seems much of Wednesday may end
up being dry. Mild with overnight lows in the 40s and daytime
highs 60-65.

Then, our weather turns much more active and unsettled starting
Wednesday night, and continuing into Thursday night and even
Friday. We are watching a developing coastal system very closely
in this timeframe.

Current guidance is slowing the closed mid and upper level low
down, which brings it from lower Michigan, across OH and PA
during the day on Thursday, then finally stalls along the NJ
coast Thursday night into Friday. The 500mb and 700mb low will
be gradually strengthening as is moves just south of our area,
and will induce surface cyclogenesis off Virginia Beach
Wednesday night, with a well defined inverted surface trough
extending north into our area. This surface low is forecast to
intensify to a sub 1000mb low, while being captured by the upper
low by 00z Friday, between KNYC and KACY. The system become
nearly vertically stacked over southern NJ by 12z Friday. By
Thursday and Thursday night there will be an anomalously strong
low level easterly jet (50 kts at 850mb) transporting ample
moisture westward into our area off the Atlantic. Therefore,
increased PoPs and QPF quite a bit in this period, now going for
likely PoPs for most of the area and QPF amounts around 1 inch.

It will be warm enough for ptype to be all rain Wednesday night
and Thursday, with lows in upper 30s to mid-40s and highs
around 50-55. Then, colder air aloft quickly moves into the area
Thursday evening and night, with 850mb temperatures falling to
around -3C and 1000- 500mb thicknesses down to 534-540dm. It is
now looking more probable this would support a mix of rain and
snow, changing to wet snow over the higher elevations Thursday
night into Friday morning. Will need to monitor this coastal
system closely in the coming days to see if it may have winter
impacts on our area. The overall pattern is favorable for a
cold, wet, slow moving and possibly wintry system. The
teleconnections, including a strongly negative NAO support it.


430 AM Update...
We`ll likely still be dealing with the slow moving coastal
system much of the day on Friday, especially central and eastern
portions of the forecast area. Again, it is starting to look
cold enough both aloft and at the surface for wet snow to mix in
through at least the morning hours Friday, especially the
higher elevations. A great deal of uncertainty remains on exact
precipitation amounts and any possible snow amounts. Model
guidance now shows this system slowly exiting off to the east
Friday evening, with conditions drying out Friday night. A cold
pocket of air aloft remains overhead, so expect chilly overnight
lows down into the 30s. Then, brief upper level ridging moves
of the region for Saturday, bringing partly sunny, dry and mild
weather with highs in the upper 50s to lower 60s. Another upper
level trough begins to approach for Sunday and next Monday.
Details remain uncertain on the exact timing and organization of
this system; therefore went very close to the blended (NBM)
guidance for this portion of the extended. This gave a slight
chance to low chance for rain showers with seasonably cool
temperatures. Will need to wait for guidance to better resolve
this system for clearer details on this portion of the forecast.
However, overall the weather pattern looks unsettled and cool.


A stubborn upper level low will slowly move into Pennsylvania by
this evening. This system will continue to pull moisture into
the area out ahead of it, with plenty of low clouds and bands of
rain showers.

A steadier band of rain will redevelop by later this morning close
to or just northeast of an ITH-BGM line, with another band of
precip working in from the southwest later in the day as the
upper low itself lumbers into western PA. Low clouds in the
MVFR to IFR range will continue even between precip bands.


Tuesday through Wednesday...Low clouds break up Tuesday morning
with VFR prevailing over most of the area most of the period.
One exception being with a few showers and brief restrictions
possible over the Finger Lakes Tue afternoon/evening.

Wednesday Night through Friday...More unsettled weather with
restrictions as rain and low clouds return. Possible wintry mix
later in the period.




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