Area Forecast Discussion
Issued by NWS Binghamton, NY

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883
FXUS61 KBGM 180226
AFDBGM

Area Forecast Discussion
National Weather Service Binghamton NY
926 PM EST Sat Feb 17 2018

.SYNOPSIS...
A coastal storm will spread snow into our region from south to
north through tonight. Milder weather will return for Sunday
and continue for the next several days.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
930 PM update...
Forecast working out well with no significant changes. Snow
intensity increasing across central New York/northern
Pennsylvania at this time due to enhancement from jet dynamics.
Activity will be winding down shortly after midnight as low
pressure moves quickly out to sea.

255 PM update...
The winter weather advisory has been expanded into Wyoming,
Susquehanna, and Delaware counties. The latest models have come
in with slightly higher QPF under the favored upper level jet
region, so we trended toward WPC`s higher snow amounts.

Though the storm is a quick hitter and quickly exits to the
north and east overnight, the dynamics favor advisory criteria
snowfall over a several hour timeframe as the upper level trough
goes negative tilt.

We now expect 3 to 4.5 inches of snow in the advisory areas
over NY, and 2.5 to 3.5 inches of snow in the PA advisory areas.
Outside of flagged areas, a general 1 to 3 inches of snow will
fall.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
A few light lake effect snow showers are possible early Sunday
downwind of Lake Ontario. Otherwise, building high pressure will
yield clearing skies.

Warm advection will strengthen Sunday afternoon with 925mb
temperatures rising to around -1C to -2C along the NY/PA border.
Surface temperatures will rise into the lower-40s.

A warm front will approach the region Sunday night. At this
point it appears precipitation will hold off until after
sunrise. Increasing clouds and continued warm air advection will
cause temperatures to hold between 25F and 30F for most of our
region.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Downstream amplification of the flow aloft continues across the
eastern half of the country Monday, as an upper-level trough deepens
across the western U.S. This should result in a frontal system to
become nearly stationary just to our north/west (from Central
Michigan into southern Ontario/Quebec) by Monday night as the upper
flow becomes nearly parallel to the the surface.

A deep southwesterly flow (more-or-less) at all levels early in the
week will result in the transport of copious amounts of moisture
into our area. Some of this flow will likely originate from the
western Gulf of Mexico, where data from both the GEFS and
operational model runs indicate high values of IVT and precipitable
water over our area (both near climatological maxima for mid-
February). Most of the deeper moisture should pool in vicinity of
the surface boundary, wherever it precisely winds up. We should all
see some possibility of rain through Tuesday, regardless. Due to
expected location of the front, northern and western areas will
likely see the greatest coverage of precipitation, as well as the
possibility of some locally heavy rainfall. Stay tuned.

Another consequence of the deep southwesterly flow will be warmer
temperatures. Strong low-level warm advection could allow 850mb
temperatures to reach between 8 and 9 degrees Celsius across the
region. The result may be near record high temperatures by Tuesday,
especially in locations which don`t receive as much rainfall.

Big picture-wise, the upper-level pattern remains largely unchanged
in the Day 4 through 7 period. We`ll likely remain in generally
southwest flow aloft, given a continued presence of a positively-
tilted trough over the western United States and ridging (of varying
degrees) over the Atlantic. This should keep temperatures above
climatological means for late February.

Subtle nuances exist, though. It looks like a bit of energy could
get sheared off from the longwave trough Tuesday night. As this
shortwave energy moves eastward across the Upper Midwest and Great
Lakes regions, it will likely provide enough momentum to push the
front through the forecast area as a cold front by sometime
Wednesday evening. When this happens, the greatest coverage of
precipitation should shift to our south as weak surface ridging
moves toward the Northeast U.S.

Big question during this time period will be extent our region dries
out. The upper-level support providing some of the forward momentum
of the front has to end sometime, which could probably result in the
front weakening or (again) becoming stationary. Some of the medium
range models indicate this could occur sooner rather than later, and
want to keep the frontal system a little farther west. For now, I
still think there may be enough of a westerly/northwesterly low-
level component such that we`re able to get some drier air parts of
the forecast area for Thursday. The exception may be across my
southern counties, who`ll be closer to the front.

Regardless of what happens Thursday, moisture starts to deepen again
heading into Friday in advance of the next frontal system.
Evolutionary details in the medium range model world are still up
for debate, but it looks like a more significant piece of shortwave
energy will eject from the longwave trough Friday, aiding in the
development of low pressure somewhere across the Mid-Mississippi or
Ohio River Valleys. The front should move into western parts of our
region by Saturday before becoming nearly stationary. With
perturbations continuing to move across the region in the
southwesterly flow aloft, the odds of precipitation will greatly
increase heading into next weekend.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
A coastal system will bring a period of snow to all the
terminals this evening through late tonight. In general
conditions will drop into the IFR/Alternate Min category with
the lowest most persistent restrictions expected at KBGM/KAVP.
The snow will end across the terminals between 07Z-09Z but
ceilings will remain in the MVFR/Alternate Required category
until mid morning when VFR conditions are forecast.

Southerly winds at 5 to 10 knots becoming westerly late tonight
and increasing Sunday morning at 8-12 knots.

Outlook...

Sunday night...VFR.

Monday through Wednesday...Occasional rain showers and
restrictions as several disturbances move through the region.

Wednesday night...Restrictions likely in mixed rain/snow
showers.

Thursday...Primarily VFR.

&&

.BGM WATCHES/WARNINGS/ADVISORIES...
PA...Winter Weather Advisory until 4 AM EST Sunday for PAZ039-040-
     043-044-047-048-072.
NY...Winter Weather Advisory until 4 AM EST Sunday for NYZ057-062.

&&

$$
SYNOPSIS...DJP
NEAR TERM...DJP/RRM
SHORT TERM...DJP
LONG TERM...DAB
AVIATION...RRM



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