Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
656 PM EST Sat Dec 7 2013
a cold flow off the Great Lakes will keep skies mostly cloudy across
western and north-central New York through this evening...along with
lingering snow showers east and southeast of the Great Lakes. High
pressure building over the region will bring some clearing overnight
before clouds increase ahead of an approaching warm front on Sunday.
The front will bring a mixed bag of precipitation Sunday night
before a cold front crosses the region Monday with seasonably cold
temperatures along with the potential for lake effect snows through
much of the coming week.
Near term /through Sunday/...
have issued a lake effect Snow Advisory for Oswego County for the
remainder of the overnight and through 15z Sunday. Regional radars
display a lake effect snow band...becoming less cellular this
evening now dropping southward into Oswego County. Off Lake Erie
light snow showers and flurries fly generally south of Route 20
..and also along the southern shoreline of Lake Ontario. Infrared
satellite imagery displays lake plume of moisture off both Lake
Huron and Georgian Bay within a cold cyclonic flow aloft...with the plume
off Georgian Bay feeding a band of lake snow along the longer axis
of Lake Ontario.
Off Lake Ontario...surface analysis this evening display a northwest
wind across the northern shoreline of Lake Ontario and across the
north country...including northwest at Watertown New York. South of
the Lake A west to southwest flow is found. This wind
flow...combined with the added moisture from upstream connections to
Georgian Bay is producing a healthy band of snow that is now
dropping southward across Oswego County. Moisture profiles display
plentiful moisture from the surface upward through about -18c...and
with the low level lift from surface convergence...this will make
for prime dendritic snow growth overnight. Latest BUFKIT sounding
and moisture profiles suggest this layer of moisture within the
prime -12c to -18c snow growth zone should last through the
overnight and into the morning hours Sunday. This seems plausible
given the latest upstream lakes to our west still providing moisture
for downstream lake effect snow bands. Though our modest lake
induced equilibrium levels of around 7k feet slowly fall through the
night believe an additional 4 to 6 inches of snow should fall
overnight across Oswego County...and another inch or so on Sunday
morning before the band again takes on a cellular characteristic to
it. The band of snow should lift back to the north later overnight
as high pressure from the Ohio Valley begins to push into the region
and winds back slightly.
Off Lake Erie...synoptic moisture is not as great...with moisture
off Lake Huron passing over Lake Erie and providing for some weak
snow showers and flurries. Will continue with chance probability of precipitation through
the night...with a possible fresh inch of snow across spots in ski
County and the western southern tier north of I-86.
Sunday...Lake effect snow east of Lake Ontario will continue to
weaken and become more cellular through the morning hours. Later
Sunday there may be a short lived break in the action as surface
high pressure moves across the region. Middle and upper level moisture
will then be on the increase by afternoon as the flow turns
southeast and warm advection increases. There could be some flurries
which breaks out across the southern tier very late in the day...but
model suggestion is to hold the main activity off until Sunday night
from the system approaching from the southwest. Bias corrected
numbers suggesting high temperatures Sunday in the middle to upper 20s.
Short term /Sunday night through Tuesday night/...
Sunday night and Monday...double-barreled low pressure will lift
northeastward across the Great Lakes and Middle Atlantic States...
with the primary surface low tracking from the lower Ohio Valley to
James Bay...and a secondary coastal low lifting from just offshore
of the the Carolina coast to near Cape Cod. While the best
large-scale forcing/moisture and consequently the heaviest precipitation
still looks to remain well off to our northwest and southeast in
closer proximity to the aforementioned low tracks...a connecting
surface trough/warm front will still lift northeastward across New
York state during this time frame and bring US a decent likelihood
of some lighter precipitation. Timing-wise...the bulk of this
should come between Sunday night and Monday morning...before
quickly tapering off from southwest to northeast as a surge of
drier air spreads into the region. At this point...a model/wpc
consensus suggests a total of one to two tenths of an inch of
precipitation south of Lake Ontario...with perhaps up to a third of an
inch across the higher terrain of the north country.
With respect to precipitation type...model forecast soundings and
plan views suggest the precipitation starting off as all snow Sunday
evening...before changing over to some form of a wintry mix and
then plain rain overnight and Monday morning as warm advection
causes the atmospheric column to warm above freezing. Compared to
yesterday...the potential for icing is now looking even more
limited with the NAM/ECMWF/Gem all backing off on the extent of
the extent of warming aloft and therefore greatly limiting the
chances for freezing rain...though the GFS still suggests enough
warming aloft to possibly allow for a brief period of freezing
rain across portions of the southern tier and Finger Lakes later
Sunday night. Given this uncertainty...the relatively light nature
of the precipitation...and the rather brief window for any freezing
rain...will hold off on issuing a Winter Weather Advisory at this
time...and instead just continue to highlight the potential within
the severe weather potential statement.
As for temperatures...expect Sunday night/S lows to come fairly early in
the night...with warm air advection then forcing readings to
rise through the remainder of the night and into Sunday morning. For
most locations...highs should peak in the upper 30s to lower 40s
between late Monday morning and early Monday afternoon...before
falling back some during the remainder of the day following the
passage of a trailing cold front.
After this...the remainder of the period will feature the center of
a large and deep upper trough over eastern North America setting up
over Hudson Bay...which will in turn circulate a much colder airmass
into our region. The cold advection will be maximized Monday night
when 850 mb temperatures of -6c to -8c will drop to between -12c to
-16c...where they will then remain right through Tuesday and Tuesday
While such temperatures aloft will be certainly favorable for a lake
response downwind of the lakes from Monday night Onward...surface-
based ridging and drier air building across the lower Great Lakes
will at the same time lead to a fairly low cap of around 3-5 kft
and eventually some drying below this level. Coupled with the
lack of a prime dendritic snow growth region below this
inversion...the above inhibiting factors should keep any lake
effect snow showers east and northeast of the lakes fairly limited
in scope through Monday night and at least a good chunk of
Tuesday. In the forecast...have reflected this by keeping probability of precipitation
downwind of the lakes confined to the chance range through this
During Tuesday night...a decent shortwave will rotate through the
base of the main upper level trough...with an associated surface
reflection passing across southern Ontario and Quebec. In the
process...this latter feature will help to lift the height of the
capping inversion somewhat and supply a gradual increase in
background synoptic-scale moisture...while also swinging a weak
surface trough across our region with winds veering from west-
southwesterly to westerly with its passage. Over time...this
should result in still somewhat limited lake effect snow showers
northeast of the lakes shifting southward and gradually becoming
better organized...which has been reflected in the forecast by
probability of precipitation increasing to likely within the migrating snow bands.
Outside of the Main Lake effect areas...conditions will remain
mainly dry Monday night through Tuesday night with just a chance of
flurries at times. Temperatures will also trend noticeably colder...with
daytime highs on Tuesday only in the middle-upper 20s...and nighttime
lows Tuesday night dipping into the teens areawide.
Long term /Wednesday through Saturday/...
in the extended portion of the forecast...the center of the deep
upper level trough will only slowly drift from Hudson Bay into
northern Quebec Wednesday and Thursday...before ejecting eastward
into the Canadian Maritimes Friday and Saturday. Through at least
Thursday...this feature will maintain a broad cyclonic westerly
flow of cold air across the Great Lakes...with 850 mb temperatures
falling to as low as -18c/-20c by Thursday. Coupled with what
should be Richer/deeper moisture and a higher overall capping
inversion...this pattern will produce an environment favorable for
potentially significant lake effect snows to the east of the Great
Lakes...with their exact placement and intensity remaining
dependent on subtle smaller-scale shortwave features rippling east
through the larger scale upper trough and causing subtle
undulations in the low-level flow.
By the latter portions of the period...the medium range guidance
shows increasing discrepancies with both the timing and amplitude of
the next noteworthy surface trough...behind which a more northerly
flow of colder air appears poised to spread across the area at the
end of the week. Given the resultant increase in forecast
uncertainty...have elected to trend snow shower chances lower and
increasingly more broadbrush in nature for the latter portions of
the week. One thing that appears more certain is temperatures will remain
below average...with daytime highs remaining locked in the 20s
through the end of the week...and nighttime lows generally in the
single digits to middle teens each night.
Aviation /00z Sunday through Thursday/...
at 00z a cold west-northwesterly flow off of the lakes will result
in continued cloudiness across western and north-central New York
overnight. MVFR ceilings and visibilities will be in place southeast of the
lakes...with some local IFR conditions possible...especially across
areas east of Rochester and south of Watertown where a healthy band
of lake effect snow is expected to continue through the night.
Outside of lake effect areas VFR ceilings will be common.
Dry air advection tonight associated with building high pressure
will scatter out cloudiness away for lake influences. MVFR
cloudiness will likely linger through the night across the kjhw
On Sunday scattered low clouds will fade...however high and middle
level cloudiness will increase through the day ahead of the next
storm system. A broken layer between 10 and 15k feet is expected to
develop through the afternoon hours as winds become more easterly.
Sunday night and Monday...VFR/MVFR with snow and rain likely.
Tuesday through Thursday...mainly VFR but IFR with lake effect
snow east of the lakes.
advisory or near advisory level west-northwest winds will persist
into tonight for many of the nearshore waters...especially along
Lake Ontario due to good Overlake instability and a tight enough
pressure gradient. A brief return to lighter winds will develop
overnight and Sunday...before low pressure passes through the region
Sunday night and Monday. That feature will usher in another surge of
stronger winds...cold air and renewed marine headlines for an
extended period next week.
New York...Lake effect Snow Advisory until 10 am EST Sunday for nyz006.
Marine...Small Craft Advisory until 7 am EST Sunday for loz043>045.
Small Craft Advisory until 5 am EST Sunday for loz042.