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Area forecast discussion 
National Weather Service Binghamton New York
631 PM EST sun Feb 1 2015

Synopsis...
a significant winter storm will impact the region overnight and
Monday. Once this storm moves off the coast Monday
night...bitterly cold weather will set in again...lasting through
Tuesday.

&&

Near term /through Monday/...
6 PM update...did an update of the winter weather message issued
for our winter storm warnings to refine timing of the beginning of
the winter storm. Made some minor adjustments to the timing and
intensity of snow shield as it continues to push north and east.
Looking at the latest guidc...we may have to adjust snow amounts
up across syr-uca-rme areas and lower amnts in NE PA. Heavier snow
may reach farther north than we have advertised at this point. The
freezing rain/ice pellets line could make a run for the New York border late tonight/early
Monday. We will continue to monitor latest guidc and make changes
if enough scientific evidence holds.

Another concern is that hrrr is slower than our local
WRF...rap...nam12 and wrf_nmm and wrf_arw in bringing in the
heavier snow later tonight. We will again monitor the snow shield
as it progresses next few hours.

Dynamics for the evening and overnight are increasing warm air advection or isentropic
lift ahead of an upper level short wave trough which makes it to Ohio
to the eastern lakes by 12z. Hence we will see liftg as air flows up
the isentropes in addition to the isentropes bodily rising in
advance of the short wave trough. Hence the heaviest snow will fall
between 6z and 12z most areas. In NE PA...a slightly above
freezing layer likely will sneak north as per NAM...GFS and sref
model soundings and reach into NE PA between 9z and 12-14z. How
far north this makes it is uncertain...but models indicate at least
kavp...possibly the PA/New York border by 12-14z. Again will monitor and
with 10 PM update might have to lower amnts in NE PA. NC New York may
see the moisture from strong thermal and moisture advtns reach up
there and with higher snow ratios amnts could be higher than what we
have. Grids updated. Left snow amounts alone as waiting for more
guidc and the character of the evolving radar trends vs the hi res
model radar trends.

Previous dscn below...
3 PM sun update... the leading edge of the steadier -sn extends
from our western Finger Lakes/central southern tier zones...down into portions of
NE PA at this time. It will continue to expand northeastward through this
evening...reaching the Mohawk Valley and southern Tug Hill regions by around 02z.
It's possible this could happen a bit quicker...as existing low-level
moisture across cny/NE PA could aid in the top-down moistening process.

The main event still looks to be overnight and Monday morning (roughly
03-15z). It is in this time frame that excellent coupled jet
structure dynamics take hold...to help transport a moisture-laden
air mass into the northestern U.S. (Blended tpw imagery showing the source
nicely over the western Gomex/lower MS/Ohio vlys)...and set the stage for
strong forced ascent (excellent low-level speed convergence and a tight
thermal gradient leading to pronounced fgen over a deep lyr).
Where ptyp remains all snow...rates of 1-2"/hour could occur for a
subset of this time frame (mainly 06-12z).

The main complicating factor remains ptyp. The 12z GFS in
particular made a slight northward jog again in the cyclone track...with the
leading edge of the warm nose aloft (850-875 mb) making a run at
the PA/New York border by 12z. Sref thermal profiles give some credence
to this scenario. Although the latest NAM/rgnl Gem/ec runs are
somewhat colder...the amplified nature of the shortwave seen in water
vapor imagery at this time over the Midwest certainly opens the door to
the possiblity of a more northward storm track/more expansive shield of
mixed precipitation early Monday. Out of respect to the GFS...which has been
consistently showing this trend for several runs now...we did nudge
snowfall amts down slightly in our far southern zones...and
correspondingly upward in our northern tier of zones. Overall...this
didn't change total accums appreciably. Even if the somewhat warmer
scenario verifies...we still feel that thermal/moisture advection
will be strong enough overnight to produce a quick 4-8" of snow before
daybreak across much of the County Warning Area.

During the day Monday...as the surface low translates towards the New Jersey coast/southern
Long Island...colder air will spread southeastward through the region by afternoon.
Consequently...any areas of mixed precipitation should be back over to snow
by 15-18z. At the same time...most of the models are showing a 3-6
hour window for deformation type banding (mainly from about 15-21z)...with
the middle-level dry slot close enough for reduced stability aloft...and
an increasing 700-500 mb fgen band shifting across cny/NE PA. The
best chance for more persistent snow banding (addtnl accums) should
be near and east of the I-81 corridor. When all is said and done...we
still expect storm total snowfall of 6-10" in our far northern and southern
zones...with a slightly heavier stripe of 8-12" in the middle (locally
higher amts (up to around 14") most likely towards
Chenango/Otsego/Delaware cntys).

As alluded to above...temperatures will be falling sharply Monday afternoon...with
bitterly cold wind chills becoming more of an issue with time. More on
this in the following section.

&&

Short term /Monday night through Wednesday/...
Arctic are will spill back down from Canada on the back side of
the cyclone. Apparent temperatures for the north and East Range
from -10f to -18f overnight, borderline for a Wind Chill Advisory.
We won't consider an advisory at this point, as we don't wish to
distract from the current storm scenario.

After a dry, cold day Tuesday...including some weak lake activity
to the northwest...another wave will dip down across New York late
Tuesday into Wednesday. This system will have limited moisture but
should still produce 2 to 3 inches of new snow.

The real impact of the wave will be to usher in another Arctic
blast for Thursday.

&&

Long term /Wednesday night through Sunday/...
a large scale trough over the northeastern United States will
continue to keep our temperatures well below normal.

A weak departing cyclone will slide eastward Wednesday night,
bringing additional snow showers and a second shot of Arctic air.

Thursday appears particularly cold. 925mb temperatures are in the -17c
t0 -20c range according to the European model (ecmwf). This airmass will yield
maximums in the single digits to low teens. Friday morning looks
frigid, with widespread -5f to -15f temperatures forecast. The
rural valleys will be even colder.

Some moderation is possible on Saturday as a southern ridge
expands into the middle-Atlantic region. However temperatures will
remain below normal.

&&

Aviation /23z Sunday through Friday/...
a powerful storm will spread snow from southwest to northeast over
the next several hours. The snow will arrive in avp and Elm
between 18z and 19z, bgm and ith between 20z and 22z, and rme and
syr between 01z and 03z.

The snow will lower visibilities to between 1sm and 2sm, with
lower visibilities possible overnight as the snow intensifies.
Ceilings will likely begin as MVFR and trend downward to IFR
overnight. A long period of IFR conditions is forecast before the
ends late Monday afternoon.

Winds will shift to the east at 5 to 10 knots.

Outlook...

Monday...IFR restrictions in snow.

Monday night...improvement to VFR from S to north.

Tuesday/Tuesday evening...VFR.

Tuesday overnight/Wed/Thu...possible restrictions due to snow
showers.

&&

Bgm watches/warnings/advisories...
PA...Winter Storm Warning until 4 PM EST Monday for paz038>040-043-
044-047-048-072.
New York...Winter Storm Warning until 4 PM EST Monday for nyz015>018-
022>025-036-037-044>046-055>057-062.
Winter Storm Warning until 4 PM EST Monday for nyz009.

&&

$$
Synopsis...mlj
near term...djn/mlj
short term...djp
long term...djp
aviation...djp

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