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fxus61 kbgm 080556 
afdbgm

Area forecast discussion
National Weather Service Binghamton New York
1256 am EST Thu Dec 8 2016

Synopsis...
lake effect snow showers will develop over New York and far northern PA
on Thursday, and become more potent heading into the weekend.

&&

Near term /through today/...
930 PM update...

In the broad southwest flow ahead of a closed upper low south of
James Bay, some vorticity at 500 mb is causing some very light
snow in southern Missouri right now. Why mention light snow in mo?
Well, as the cut off low moves into far western Ontario by 12z
Thursday, this channeled vorticity sneaks up toward the New York/PA
border. The higher resolution guidance such as the hrrr and
arw/nmm continue to show some scattered flurries or very light
snow with this between 09z and 14z tomorrow. We already had a
chance for snow across much of New York but I increased pops toward the
New York state line and into northern PA to account for this. Otherwise
no big changes to the forecast. We have fielded a few questions on
social media about why we lowered snowfall amounts for Thursday
night through Friday night. If have a few moments, we made a quick
but detailed video on some of the challenges of forecasting lake
effect snow. You can see it at www.Youtube.Com/nwsbinghamton. The
previous afd is below...



205 PM update...
a potent polar air mass will plunge into the base of a trough
rotating through the northeastern U.S., Activating the lakes early
Thursday.

We largely followed the lake bands produced by the CMC regional
guidance, as these look realistic in terms of placement and quantitative precipitation forecast.
However, we added in a larger area of light snow surrounding the
bands over central NY, as persistent northwest flow should
generate light precipitation nearly to the New York/PA border by mid-
afternoon.

Most New York sites will not make it out of the 20s on Thursday.

1030 am update...
with precipitation moving out and clouds thinning, temperatures
are climbing quickly this morning, with several observations
already at or above the projected maximums.

We raised forecast maximums this afternoon.

&&

Short term /tonight through Saturday/...
lake effect snow watches and the warning for northern Oneida
County remain in place. The main change with this update was to
lower snowfall amounts as some favorable factors for high amounts
of snow are now becoming less favorable.

A lake effect band of snow north of our area Thursday evening
should impact northern Oneida County through 06z Friday with a
flow between 270/275. Inversion heights are well above 10,000
feet, with a good fetch over lake with moderate instability. The
snow growth region is a bit lower than yesterday and the models
are still forecasting shear. This may Widen the band somewhat but
also make it more diffuse. The other question mark is some models
are faster with a trof, which would shift our winds into the
northwest and sink the band farther south than currently
anticipated. We lowered amounts a bit to compensate for some of
the concerns above but overall this area remains the most likely
area to see significant snowfall in our area, at this Vantage
Point.

Early Friday the trof mentioned above will swing through and
disrupt the snow band while moving it south. Eventually a steady
300 to 310 wind flow will set up Friday and Friday night. The
inversion heights do lower as expected but they are 2 to 4kft
lower than the runs of the models yesterday. In addition while not
perfect, the snow growth region is a bit higher than previously
thought and the best lift in the atmosphere may not line up as
well. Model qpfs remain very low and while not usually at all in
reality in lake effect events, with the low quantitative precipitation forecast and the slightly
less favorable conditions just 24 hours removed from yesterday, it
was hard to argue in not lowering amounts. The watch will remain
in place and hopefully we can have more clarity tonight with the
0z runs. We may be looking at a widespread lake effect advisory
area vs. A warning but time will tell. Speaking of an advisory,
folks in northern Cortland, Chenango, Delaware and Otsego
counties will remain close enough to lake snows that advisory
level snows are possible here. We will mention it in the hazardous
weather outlook.

&&

Long term /Saturday night through Wednesday/...
210 PM update...

A persistent trough over the northeastern U.S. Will keep the
weather stormier than normal, while temperatures remain on the
cool Side. Lake effect snows will be ongoing Saturday night, with
most of the activity migrating north of Oneida County on Sunday.

A powerful storm will move up the Ohio Valley on Monday, bringing
another round of snow, possibly mixing with rain during the
warmest midday hours.

&&

Aviation /06z Thursday through Monday/...
though the sky will be usually broken or overcast, generally VFR
conditions are expected this taf period except during lake effect
snow showers for ksyr-krme-kith-kbgm. Due to the amount of dry air
initially, confidence has decreased for Lake Erie snow showers
reaching over to ksyr-krme 12z-16z and thus these have been
removed from the tafs. However, kith and kbgm still do stand a
decent chance of Lake Erie snow showers passing through this
afternoon with visible reducing to at least IFR. The chance is less at
kelm so not in taf, but brief restrictions will be possible.
Then, there is good confidence that around 03z- 06z Friday, a
squally Lake Ontario band will drop through ksyr-krme. IFR visible
has been put into the tafs for then, but there is some potential
for less than a mile visible. Generally light southwest wind early
this morning will veer more westerly during the day while picking
up into 9-14 knots range with gusts approaching 20 knots.

Outlook...
Friday through Saturday night...restrictions at ksyr in lake
effect snow; possible occasional restrictions in snow showers or
flurries for krme-kelm-kith-kbgm. Kavp mainly VFR.

Sunday through Sunday night...widespread restrictions becoming
more likely with a general light snowfall.

Monday...restrictions possible in sct. Snow showers.

&&

Bgm watches/warnings/advisories...
PA...none.
New York...Lake effect snow watch from this evening through late Friday
night for nyz017-018-036-037.
Lake effect snow warning from 11 am this morning to 7 am EST
Friday for nyz009.

&&

$$

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