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fxus61 kbgm 170521 

Area forecast discussion
National Weather Service Binghamton New York
1221 am EST sun Nov 17 2019

high pressure will continue to bring a cold but dry weekend.
Our next system will bring the chance for mixed precipitation
Sunday night through Monday night. High pressure returns mid


Near term /through today/...
950 PM update...
no major changes made to the forecast this evening. Current
temperatures across the region are running a few degrees warmer
than the previous forecast. There are a few high clouds
streaming across the region this evening as well...which may be
helping to keep temps from falling as far are thought. Think
we'll still get quite cold tonight, but it might take a bit
longer than previous thought.

Previous discussion...
high pressure continues to dominate our weather this afternoon
with ample sunshine due to very dry air in place (dew points
mainly in the single digits, with even some negative values in
spots). Quite remarkable for this time of the year to see the
entire forecast area cloud-free (aside from a very few high
level clouds), but this is to be expected with such a dry
airmass. Temperatures are a few degrees warmer than previously
forecast at some locations, but still overall chilly with highs
only topping out in the upper 20s to upper 30s.

Main story for tonight will be the very cold temperatures (near-
record cold) due to ideal radiational cooling conditions. On top
of that, some snow cover remains in portions of central New
York, which will further aid the radiational cooling process. A
blended model approach using nbm for tonight's temperatures
resulted in temperatures that seemed a bit too high, likely
because some models typically struggle with temperatures in
radiational cooling situations. Going with mainly a blend of the
adjmet, adjmav, and previous official forecast, resulted in
plenty of single digit lows in a good portion of central New
York and the Catskills (portions of Oneida County may even
approach 0 degrees), with teens across northeastern Pennsylvania
and the extreme southern tier of New York.

Temperatures will moderate by Sunday afternoon and highs will
climb into the mid to upper 30s as high pressure slides east and
weak southerly flow develops over the region. While a bit more
cloud cover than today, still expecting a mostly sunny day for
the majority of the area.


Short term /tonight through Monday night/...
355 PM 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 European model (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 severe weather potential statement 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 New York 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 New York 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. European model (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.


Long term /Tuesday through Saturday/...
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 New York 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 northwest flow expect a decent chance for More
Lake effect snow showers.


Aviation /05z Sunday through Thursday/...
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.


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



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