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Area forecast discussion 
National Weather Service Binghamton New York
659 am EST sun Dec 21 2014

Synopsis...
a complex storm system will track up through the Ohio Valley to
the Great Lakes region during the middle of next week, including
Christmas day, and bring rain and gusty winds. There is a chance for
light freezing rain in some areas at the onset of the
precipitation Monday night into early Tuesday. Rain showers will
mix to snow showers on Christmas day as colder air works into the
region behind this storm.

&&

Near term /through Monday/...
another day of clouds which will make day 14 in a row. Optimistic
model soundings from just 24 hours ago are much more pessimistic
for sun chances today. 0z NAM BUFKIT soundings still show a thin layer
of moisture trapped underneath an inversion, which has been a
broken record for US now. At best we may see a few breaks in the
cloud cover, not a total clear out, late in the day over the far
west and south. While forecast soundings support this, extensive
clouds back to our west through lower Michigan and Ohio do not. A
stray flurry or two is possible through daybreak but overall most
will remain dry. With the cloud cover again today, afternoon highs
will only be about 5-6 degrees warmer than temperatures right now.

Monday may be our most realistic shot at sunshine as the flow
turns more southerly, and this may help to lift any low clouds to
our north. Right now observation support this back over Kentucky and
Tennessee. As our middle week storm takes shape over the central part
of the country, hopefully we can finally see a brief break in the
clouds before we turn unsettled again.

&&

Short term /Monday night through Tuesday night/...
415 am update...
period will feature southwesterly flow aloft...and a slowly
yielding ridge at the surface. Wave embedded within the
southwesterly flow will attempt to bring very light rain across
the area Monday night into Tuesday morning...with additional waves
late Tuesday-Tuesday night. Because of the amount of warm air
aloft...precipitation appears that it will be exclusively liquid.
For some locations /mainly eastern parts of our area/ that may
present a very light freezing rain possibility Monday night- early
Tuesday.

European model (ecmwf) and Canadian models still bring light quantitative precipitation forecast into the area with
that first wave Monday night-early Tuesday...yet NAM and
especially GFS have very little. Either way...it will be very
light precipitation that will have to fight surface ridge of high
pressure extending down from strong high over the Canadian
maritime provinces...and dry middle levels. A lot of it may turn out
to be virga. Easterly flow against the Poconos-Catskills will mean
light rain chances will be best there due to upsloping...or at
least drizzle...with only slight to low chances for majority of the
area. The cold air damming via easterly flow will also mean light
freezing rain possible on the front end of the wave until
temperatures are able to get above freezing. The usual suspects
will be prone to a very light icing...Poconos-Catskills-Mohawk
Valley-Tug Hill...but of course that will depend on actual
precipitation which itself is not certain. Midmorning Tuesday
Onward...above freezing for entire area and thus only rain for
precipitation type.

High pressure ridge gradually yields into Tuesday night...while
deeper moisture arrives from increasingly moist SW-south-southwest flow along
with additional shortwaves embedded within. Thus rain chances
areawide will increase significantly especially towards dawn
Wednesday.

&&

Long term /Wednesday through Saturday/...
415 am update...
forecast adjusted slightly for wpc guidance and model trends.
Very mild temperatures Christmas evening...including into the
night...before cold air advection arrives Christmas day. Also quite
wet with precipitable water values a good 3-4 Standard deviations
above normal...and southerly component of 850mb jet around 3
Standard deviations. While we have areal average quantitative precipitation forecast of roughly
half to three quarters of an inch through Wednesday...rainfall on a
localized scale could be heavier. Models still disagree a bit on
how long it takes precipitation type to change from steady rain to
scattered snow...but trend is slightly later...so Christmas day
may include both rain and snow showers initially before all snow
showers by later in the day. Coverage of those showers Thursday will
be highest in northern to central New York...with significantly
fewer showers in twin tiers and especially towards Wyoming Valley
of nepa due to potential dry slotting as mentioned below.

Previous discussion...
medium range models are still in good synoptic agreement of the
upcoming storm system. By Tuesday night the potent upper level trough
will be located just along and east of The Rockies... and is
expected to dig southward into the far southern portions of Texas.
The northern stream of the trough is expected to push an occluded
surface low northeast from the Great Lakes region into Canada... while
the southern stream of the trough is expected to induce
cyclogenesis over the southeast Continental U.S.. these two features as they
move northeast will result in showers across the County Warning Area through early
Friday morning.

All activity by Tuesday night is expected to be rain as strong warm air advection will
be present over the region. Showers at this time are expected to remain as
rain until 06z on Thursday. The European model (ecmwf) is quicker to transition
rain over to snow than the GFS. It is still to far out to Pin
Point how much snow will fall with this system Thursday morning...
but snow accumulations look minimal outside of lake effect country
as we may still be in the dry slot region Thursday.

As mentioned before winds may be a potential impact from this
storm on Thursday as colder air surges into the region. Temperatures Wednesday
afternoon will be very warm for this time of year... rising into
the low 50s. Colder Pacific air will filter in behind this system
as it moves out of the area... resulting in high temperatures only
reaching the upper 30s to low 40s on Thursday. Friday and Sat temperatures are
expected to range in the upper 30s to low 40s.

We are keeping a close eye on this storm. For travel concerns
please pay attention to future forecasts.

&&

Aviation /12z Sunday through Thursday/...
persistent moisture underneath an inversion will keep clouds
across the terminals through tonight.

MVFR ceilings expected for most of the terminals through late morning.
By later this afternoon enough drier air may move into all
terminals except kbgm that while still fairly cloudy, our deck may
raise to 5kft or higher. Mvfg ceilings look most likely to persist at
kbgm and through tonight.



Winds will be light through the period. Gradually winds pick up
out of the southeast tonight around 5 kts.

Outlook...

Monday...mainly VFR.

Monday night to Thursday...restrictions with developing light mixed
precipitation Monday night-early Tuesday...then periods of rain Tue-thurs.

&&

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

&&

$$
Synopsis...heden
near term...heden
short term...mdp
long term...kah/mdp
aviation...heden

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