Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Albany New York
931 PM EST Thursday Dec 12 2013
a cold front will push from the Ottawa Valley through the region
Friday. It will usher in another surge of very cold air into the
region and reinvigorate lake effect snows into the western
Adirondacks and western Mohawk Valley. High pressure will crest over
the region Friday night. Saturday a storm will organize in the Ohio
Valley...then reform on the middle Atlantic coast Saturday night...and
move northeast Sunday. It will bring a moderate snowfall to much of
the region this weekend.
Near term /through Friday/...
Lake effect bands are a little slow in extending well inland so
have indicated this in the probability of precipitation grids.
Some minor changes to the sky cover...temperatures and dew points
through tonight. Details on the lake effect snow bands that should
organize better later tonight are described in the previous afd
Surface high pressure will ridge from the Ohio Valley towards
Carolinas as 500hpa trough is sharpened by a series of digging short
waves. The strongest of these short waves dives southeast from ont tonight and
drives cold front through fca Friday. Friday afternoon high surface hi ridges from ont into
New York/new eng.
While the cold front is likely to trigger snow squalls this pattern will
more significantly drive the lake response during this period. This
morning Main Lake effect band is weak is oriented along 240
vector...as considerable shear exists across lake ont...and models
soundings are capped at 5kft...in spite of extreme niziol
These conds will change during this evening becoming more supportive of
lake response as the strong short WV moves into fca...cold front approaches
from north reaching the north tier of fca by 09utc. Shear diminishes and cap
rises to well above 10kft. Band will reinvigorate and be mainly
along the 270-280 vector into north Herkimer and north Hamilton Colorado tonight.
However by 4am and Onward the band is along 290-300 vectors where it
persists into Friday morning. Capping begins increasing Friday midday and by
late afternoon its capped off at 3kft as instability class diminishes to
moderate. While inertia will keep band going into afternoon it will
quickly diminish during the afternoon as warm air advection ahead of next system
begins to impact west fringes of fca...and cap hammers down.
This is supported by the large scale environment in the GFS/NAM/WRF.
Given this will likely upgrade les watch in north Herkimer County to a
warning and issue a les advisory for Hamilton and S Herkimer Colorado.
Otherwise away from lake ont vrb scattered-broken clouds scattered -shsn mainly forced
by terrain and west/squalls with cold frontal passage particularly when it
aligns with the favored lake effect moisture channel Friday morning.
With cold front approaching wind gradient will hold up west-SW winds around
10kts overnight. Afternoon cold frontal passage northwest flow and well mixed
layer will increase winds to 10-20kt with gusts over 30. Temperatures will
remain well below normal during this period with lows tonight in the
single digits to teens and -10 to near 10 Friday nt.
Short term /Friday night through Sunday/...
potentially significant winter storm impact this weekend.
However... no winter storm watches were issued with this package as
confidence of snowfall of 9 or more inches in a twenty four period
remained below 50 percent.
A very cold Arctic air mass will be entrenched over the region
courtesy of strong high pressure to the north. This high will slide
to our east by Saturday morning. An east to southeast flow will
induce isentropic lift as warmer more moist air to the southeast of
the region is lifted over the dome of air. Clouds will quickly
thicken up and light snow will break initially south of the capital
district Saturday morning. By afternoon...light snow will likely
overspread the entire County Warning Area including New England.
Vorticity...spun off an upper low over Southern California will
develop a surface low pressure along an increasing baroclinic zone
this weekend over the southeastern United States. This storm will
rapidly track to Cape Hatteras by Sunday morning.
Meanwhile...further north and west...a separate system in the
northern stream will be digging a middle latitude trough into the Great
Lakes. If this system were to phase with the southern storm...this
could be an epic storm a lot like the storm last February that
buried our southeastern zones.
However...no models are indicating this to happen. Instead...the
southern storm is forecast to track northeast (not north-northeast)
which takes it off the coast of New England. At the same time...the
upper air low looks to move to our north...keeping a separate entity
for the coastal storm.
This makes the ultimate snowfall forecast challenging because...
1) ascent with the northwestern system could be confined to our
western zones while frontogentic forcing with the coastal storm
might get pinched to our east...leaving much of our area with much
weaker forcing and lighter snowfall amounts.
2) while it looks cold enough for mainly snow (possibly mixing with
some sleet and or freezing rain well south of the capital
district)...snowfall to liquid ratios will likely start high with
good dendritic snow growth (maybe as high as 15:1). However...as a
warm nose develops in the column later Saturday night they will
likely drop closer to 10:1 as result of riming snow flakes...making
for a more compact but harder to shovel snow). Of course any
changeover to sleet or freezing rain south would further lower any
3) there could be some shadowing in the Hudson Valley and Taconics
for awhile Saturday night due to an easterly wind in the low levels
levels of the atmosphere...but likely not at the surface). This
could lower amounts a little.
This all said...we are fairly confident of a moderate snowfall event
(4-8 inches) inch at this time with of course the potential for this
change. It looks like a generic snowstorm for most if not our entire
forecast area. Any minor wind issues should be confined to the
higher elevations where a few gusts to 30 miles per hour are possible...mainly
to the east of the Hudson Valley. There is very little if any threat
of power outages since we are looking at mainly a dry snow. The main
impact will be slippery roads.
Again...no winter storm watches were issued at this time.
The steadiest and most moderate snowfall looks to be Saturday night.
By Sunday morning...there is a chance the even the ice could be gone
in the clouds leaving US with a little freezing drizzle or snow
grains and not much additional accumulation.
As mentioned temperatures will be cold throughout the storm...only
reaching the teens to lower 20s south on Saturday...falling very
little if any Saturday night. On Sunday...look for highs to reach
around freezing in the middle Hudson Valley...25-30 rest of valley
locations...closer to 20 further north.
Long term /Sunday night through Thursday/...
the coastal storm will be well to our northeast by Sunday
night...likely bringing yet another round of Arctic air back into
the region. There might be an additional boundary with the
resurgence of Arctic air and this might trigger more snow showers
and snow squalls Sunday night. Then...the door is open for another
potential lake effect event late Sunday into Monday...mainly across
the Adirondacks but possibly into the Mohawk Valley as well.
Also...upslope lake enhanced snows are possibly across the higher
terrain to the east of the Hudson Valley and maybe even the
Catskills. At this point...any significant additional snowfall
amounts look confined to the Adirondacks and perhaps central Mohawk
Monday night into Tuesday...models forecast a potent clipper system
to work to the north of the area...bringing possible snow showers of
its own...or possibly snow squalls if its own. Again...the most
primed areas would be the Lee of Lake Ontario...but a snow squall is
possible just about anywhere on Tuesday. Will keep everyone posted
on this possibility.
More Lake effect snow behind this clipper through Wednesday into
Thursday across the Adirondacks and Mohawk valleys while everyone
else remains mainly dry with blustery cold brisk conditions.
Temperatures will continue to average below normal during the
extended...generally in the 20s to near 30 in valley
locations...teens higher terrain. Lows will average zero to 10 above
north...10 to 20 south.
Aviation /03z Friday through Tuesday/...
generaly scattered variable broken at above 3000 feet through the
night at kgfl...kalb and kpsf with just scattered at kpou.
Adjusted the timing of potental scattered snow showers to between
09z-15z...and too scattered to include more than a vcsh. Snow
showers should exit after 15z.
West winds winds will become southwest around 10 knots tonight...then
after the reinforcing cold front and snow showers exit by afternoon
will shift to the northwest at around 15 knots with gusts around
friday: high operational impact. Snow showers likely.
Friday night: no operational impact. No sig weather.
Saturday through sunday: high operational impact. Snow.
Monday: no operational impact. No sig weather.
Monday night: low operational impact. Slight chance of -shsn.
Tuesday: moderate operational impact. Chance of shsn.
no Hydro related concerns are expected through early next week.
Mainly snow will fall this weekend. Temperatures will be well below
normal and ice will continue to form on area rivers..streams and
For details on specific area rivers and lakes...including observed
and forecast river stages and lake elevations...please visit the
advanced hydrologic prediction service /ahps/ graphs on our website.
New York...Lake effect snow warning until 1 PM EST Friday for nyz032.
Lake effect Snow Advisory until 1 PM EST Friday for nyz033-038.