Area Forecast Discussion
Issued by NWS Binghamton, NY

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FXUS61 KBGM 170902

Area Forecast Discussion
National Weather Service Binghamton NY
402 AM EST Sun Nov 17 2019

High pressure slides east today and temperature will be a bit
warmer this afternoon. Our next system will bring the chance
for mixed precipitation late tonight through Monday night. High
pressure returns again mid week.


345 am update... After cold start this morning, high pressure
will shift eastward and temperatures will moderate this afternoon
with highs climbing into the mid to upper 30s in some areas.

Coastal low pushes north tonight along the east coast and this
provides a very tricky forecast for early Monday morning. Models
increase low level moisture with temperatures increasing aloft.
Meanwhile, cold air remains trapped at the surface and ground
temperatures should still be well below freezing due to the
airmass we have had stationed overhead the last few days.

Most guidance is now in agreement that some light freezing rain
or drizzle develops overnight, but there is some concern that
guidance is over-doing this moisture, and it may have a tough
time overcoming the very dry air entrenched over the region.
However, the consensus is that there will likely be at least
some pockets of light freezing rain and drizzle that will
develop by Monday morning, especially along the Eastern
Catskills and Poconos as an easterly upslope flow should be
enough to slightly enhance precipitation in those areas. Have
issued a winter weather advisory for counties we feel most
confident of this occurring at this time, however, confidence
remains low in how far westward this moisture will spread by
early Monday and the advisory may need to be expanded at a later

Temperatures will warm through the day on Monday, which further
complicates the forecast for freezing rain/drizzle Monday
morning. Eventually any freezing precipitation will turn to all
rain by Monday afternoon.


355 PM Update...No major changes to the short term period. Still
a very complex, albeit, likely lower impact winter weather
forecast. Minor changes to reduce the amounts/intensity of any
light freezing rain or drizzle Sunday night. It should warm up
just enough (mid to upper 30s) during the day Monday to prevent
much in the way of any icing impacts (except perhaps the highest
elevations of the western Catskills). Main timeframe to watch
for the light wintry mix now looks to be after sunset Monday
evening into Monday night. Same model characteristics persist,
with the ECMWF showing more phasing and therefore more lingering
precipitation over our central and eastern zones trough the
night. Thermal profiles are still complex, with a mix of
rain/freezing rain/ice pellets in the evening...then as cold air
advection takes hold after midnight any lingering precip
changes over to light snow or snow showers. Still have some
light ice accumulations in the forecast; mainly along and east
of I-81. Also have some very light snow accumulations of a light
coating to 1 inch areawide from this system. Am content with
continuing to mention this event in the HWO for now, as
confidence in exact details still remain low.

Previous Discussion Below

405 AM Update...
Main concern for the short term period will be prospects for
mixed precipitation including possible ice from freezing rain.

This period will be very tricky in terms of precipitation type,
coverage, and amounts. Models all carry variations of a mixed
precipitation thermal profile yet with enough differences to
have meaningful impacts on coverage and amounts of potential ice
from freezing rain, and to a lesser degree snow. And indeed,
there are questions as to when and whether precipitation even
occurs for some locations. Uncertainty is always in play with a
mixed precipitation event, but in this case confidence is even
lower than usual for this type of situation. This makes it
important for anyone with travel plans to closely monitor the
forecast the next day or so as these details become clearer.

The thermal profile itself, while exhibiting plenty of spread
at any given time, will also be constantly in flux as southern
stream wave/coastal low initially outpaces a negatively tilting
northern stream trough. Operational models differ considerably
on when to link the two systems, and at least for Sunday night,
whether the first one will even get precipitation into the
region. For the first phase of the event, there is high
confidence that thermal profiles will be too warm for crystals
along and east of I-88 in NY and I-81 in PA. However, near
surface air will likely be in upper 20s-lower 30s late Sunday
night to dawn Monday, due to cold air damming from a high over
northern New England-Canadian Maritimes with ridge extending
through the interior Northeast. So the question here is if
precipitation can even reach into the area as suggested by the
NAM and Canadian models, versus the GFS-ECWMF models which wait
beyond 12Z Monday. If it does, then the result will be light
amounts of freezing rain encroaching into eastern to possibly
central parts of the area that could impact the Monday morning
commute. As mentioned above, areas along/east of I-88 in NY and
I-81 in PA stand the somewhat better chances for these issues.

During the second phase of the event, the negatively-tilting
northern stream trough will swing into the area Monday afternoon
through night while merging. Here the chances for precipitation
itself is higher, yet confidence is lower in the thermal
profile and surface temperature details. This includes timing
of when ice crystals will be present within the column. ECMWF
and Canadian models also have quite a bit more precipitation;
the question is how much of it falls as plain rain before
switching to wintry mix before ending. For this phase, a larger
portion of the area has at least some potential for light ice
and/or sleet-snow amounts Monday evening-night, but again
confidence is quite low and the devil will be in the details.
Surface temperatures will teeter Monday night within a few
degrees on either side of freezing, with higher elevations as
usual a bit more vulnerable.


400 PM Update...

Pattern remains rather active through the week with seasonable
temperatures. A few lingering lake effect rain and snow showers
will be around central NY Tuesday, then a weak clipper system
passes through Tuesday night with more snow showers. Any accumulations
are looking light at this time. Highs will be in the upper 30s
to mid-40s and lows dip into the upper 20s or lower 30s. More of
the same for Wednesday with scattered lake effect snow or rain
showers around. 850mb temperatures are forecast to be around -5C
giving daytime highs of 35 to 45.

Brief upper level ridging builds in Wednesday night and Thursday
morning...which should bring a period of dry weather areawide.
Then, a fairly strong low pressure system moves into the Great
Lakes on Thursday. There are some minor timing differences in
the guidance, but at this point, it seems rain will overspread
the region from west to east Thursday afternoon or evening. It
will be plenty warm for all rain, as the southern flow of warm
air advection boosts temperatures well into the 40s (near 50 in
the Wyoming Valley). The low pressure center moves up the St.
Lawrence Valley Thursday night, with more periods of rain. Then,
a strong cold front is progged to move through the area on
Friday. This will bring strengthening cold air advection, gusty
west-northwest winds and rain, changing to snow showers. 850 mb
temperatures fall back to around -10C Friday night and Saturday.
Went a few degrees lower than the blended guidance for this
period. With the cold NW flow expect a decent chance for more
lake effect snow showers.


High pressure with mostly clear skies and VFR conditions are
expected tonight through most of day today. Clouds will increase
later in the day, but ceilings remain VFR. Moisture starts to
push in from the southeast from a coastal low and AVP and BGM
may see MVFR ceilings develop late tomorrow night.

Monday through Thursday...restrictions possible in occasional
rain and light snow. Also, freezing rain will be possible Monday
night into Tuesday morning.


PA...Winter Weather Advisory from midnight tonight to 11 AM EST
     Monday for PAZ040-048-072.
NY...Winter Weather Advisory from midnight tonight to 11 AM EST
     Monday for NYZ046-057-062.


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