Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 071807
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
107 PM EST Wed Dec 7 2016

.SYNOPSIS...
Much colder air will filter in tonight such that scattered light
lake effect precipitation today and this evening east of the lakes
will increase in intensity on Thursday, while transitioning over to
snow. Bands of lake effect snow, will become established by mid-day
Thursday east and southeast of the lakes, producing heavy snow
through Saturday.

&&

.NEAR TERM /THROUGH THURSDAY/...
For today and into tonight, much of the region will be seeing the
relative calm before the significant lake effect event that will
ramp up on Thursday. Temperatures aloft this morning (-6 to -7C) are
already cool enough to support the lake effect cloudiness seen on
visible satellite imagery over Lake Erie and Ontario. However, the
capping inversion level remains below 4kft, along with a very dry
slot of air above that through the dendritic growth zone. This will
continue through this afternoon and overnight tonight, as the upper
level low and associated synoptic moisture remain to our west over
the upper Great Lakes. That means for this afternoon and evening,
would not rule out some scattered areas of sprinkles or drizzle
under the lake effect clouds northeast of the lakes, as all the
moisture will remain below the dendritic growth zone and lake
equilibrium levels remain very low.

Overnight tonight and into early Thursday morning, have backed off
the development a plume of lake effect snow into the Buffalo and
Watertown areas on the southwesterly flow. The primary reason for a
more delayed start to the accumulating snow is due to latest model
guidance delaying the arrival of more significant synoptic moisture.
Thus while equilibrium levels rise, there won`t be much background
moisture or synoptic lift to excite the lake effect snow bands in
the early morning hours. Thus expect continued drizzle/sprinkles or
light snow showers leading up to the morning commute. Thus any
potential impacts to the morning commute Thursday would be limited
to an areas were some slick spots can form if temperatures become
cold enough for drizzle to freeze, however that is a very low
confidence treat at this point. This also means very little to no
snow accumulation for much of the Buffalo metro area, with the
exception of the far southtowns, through Saturday.

This impactful lake snow event will intensify Thursday as
instability increases under a rising cap. The flow will steadily
veer from 250 to 270 degrees during the course of Thursday as the
lake effect plume of snow develops. This will allow the plume of
moderate to heavy lake snow to settle across southern Erie county
and northern portions of Ski Country, where snowfall rates will
increase to 2 to 3 inches per hour... partially due to the enhanced
orographic lift. Meanwhile off Lake Ontario...a 240 to 250 flow will
support lake snows over Jefferson and the northern half of Lewis
County Thursday morning. As in the case of the activity off Lk
Erie...winds will veer to 270 during the afternoon. The plume of
moderate to heavy lake snow will push south across the Tug Hill in
the process. Again...snowfall rates will increase during this
southward push...largely due to increased fetch and also from
orographic lift from the Tug.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
...Significant lake effect snows to impact areas east and southeast
of Lake Erie and Lake Ontario into the weekend...

An impressive stacked storm system...seen in WV imagery churning
east across Lake Superior early this morning...will be the driving
force behind our upcoming major lake snow event. This deep system
will track due east across the heart of Ontario this afternoon
before crossing into Quebec`s air-space late tonight and Thursday. As
this slow moving feature drifts across southern Quebec to the
Canadian maritimes by the weekend...it will circulate H85 temps as
low as -16c across the wide open Lower Great Lakes. This will
establish a moderate to extremely unstable thermal profile below 10k
ft with SBCAPEs climbing to near 1000 j/kg and lapse rates below 5k
ft easily exceeding 10 deg c/km. Meanwhile equilibrium levels will
surge to around 20k ft...more than enough to support deep mesoscale
driven convection. Microphysically...the dendritic snow growth
region will average 3-4k ft deep...which is typical for lake effect
snows within a steady...cold advective regime. This thermal profile
will encourage the growth of large dendrites that should accumulate
at a rate of at least 2 to 3 inches per hour in the heart of well
organized bands.

Local research shows that the synoptic placement and track of the
stacked storm system coincides extremely well with analogs for
significant lake snows east of both lakes. Additional studies
strongly suggest that this event should become electrified...at
least during the initial 24-36 hours. Given the high inversion hgt
and placement of the -10c isotherm...there should be sufficient room
to separate charges generated by the mixed phase cloud. Lightning in
lake snows are typically within 20 miles or so of the source of
instability (the lakes)...so have tried to incorporate this into the
forecast. Have even placed a bullseye for thundersnow in the vcnty
of the large wind farm on the Tug Hill where cloud to ground
strikes are more common.

As a surface trough moves south across the Lower Great Lakes
Thursday night...the steering flow below 10k ft will veer to the
northwest. While this will keep the focus of the Lake Erie snows
over the Western Southern Tier (particularly Chautauqua and Catt
Co`s)...it will continue to push the Lake Ontario snows further
south...off the Tug. This will place Oswego County in the cross-
hairs of Mother Natures snow machine. In the process... overnight
snowfall amounts are forecast to average a foot along and within
20 miles east of the Chautauqua Ridge...with a foot and half of
snow expected in the vcnty of the Tug Hill Plateau.

Friday and Friday night...a fairly persistent 300-310 flow will keep
widespread accumulating lake snows in place southeast of both lakes.
Another foot of snow could easily accumulate during this 24 hour
period...again...focusing on the Chautauqua Ridge and Oswego county.
Amounts should reach at least advisory levels for Wayne and Northern
Cayuga Counties...so the current lake snow watches for those areas
will likely be updated to either advisories or warnings later today.

By the time we reach mid day Saturday...the lake snows should be
steadily weakening off both lakes as high pressure and drier air
build into the region...and as shear increases under the advancing
ridge. A general backing of the low level flow will probably still
send the remnants of these bands back north across the Buffalo and
Watertown areas Saturday afternoon and evening...before these die
out altogether Saturday night as the low level flow becomes too
southerly.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
While the major lake snows of the previous days will not extend into
this period...it will remain quite wintry over our forecast area.
This scenario will be supported by a longwave pattern that will
feature a deep trough over the heart of North America that will keep
a cyclonic flow of seasonably cold air over all of the Great Lakes
region. This pattern will be highlighted by a large chunk of the
Polar Vortex that will break from its anchored position near the
Pole and dive southward across central Canada during the weekend and
early next week. The robust mid level gyre will not only keep a
relatively cold pattern in place by maintaining the deep trough...
but it will help to drag a new surge of Arctic air south towards the
Lower 48. We may have to contend this airmass as we advance outside
of this forecast period.

In the meantime...a developing storm system over the center of the
country will take aim on our region for later Sunday and Sunday
night. The medium range ensembles...while exhibiting a great deal of
spread within their solutions...are in fair agreement that
widespread snow will make its way across our forecast area. While
accumulations should be anticipated with this event...confidence is
not high for significant amounts. It could be enough though to make
for a messy Monday morning commute.

Model solutions continue to diverge on Monday...as scenarios range
from the passing of an organized storm to our south...to a cold
northwesterly flow that would support some nuisance lake effect.
After collaboration with surrounding offices...have decided to broad
brush with high chc pops for now as we should have at least some
snow showers over the region.

While a cold cyclonic flow will be in place across the Lower Great
Lakes on Tuesday...there is medium confidence that weak low level
ridging should support mainly fair weather. That being said...some
nuisance lake snows will be possible east and northeast of each
lake.

Looking further out through much of the remainder of the week...
temperatures should tumble to below normal levels across our region.
A pool of <-30c H925 air over the Canadian prairies on Tuesday will
be directed across southern Ontario and Quebec on Wednesday and
Thursday as the aforementioned arctic gyre will sweep through the
base of the longwave trough and eventually become positioned over
the Labrador Sea. Downstream ridging over the Norwegian Sea may keep
this general pattern in place for the bulk of the week. This would
favor at least some of the very cold air being left over our
region...where H925 temps would average in the minus teens c and H85
temps would be in the vcnty of -20 to -25c.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
Lake effect cloudiness will persist east and northeast of lake Erie
and Ontario (near KART, KBUF, and KIAG) this afternoon through
overnight tonight. Cannot rule out some areas of drizzle this
afternoon and and overnight tonight under these lake clouds, however
the main lake effect snow threat will hold off until mid-morning
Thursday, and being shifting southward away from KBUF/KART, and
toward KJHW/KFZY. Thus expect mainly VFR to MVFR conditions to
persist at the TAF sites. MVFR becoming IFR conditions will develop
east of the lakes on Thursday, possibly clipping KART mid-day
Thursday, and then moving into KJHW by Thursday afternoon.

Outlook...

Thursday night through Saturday...IFR in lake effect snow east and
southeast of the lakes. Occasional snow showers with more brief IFR
elsewhere.
Sunday and Monday...MVFR/IFR in widespread light snow.

&&

.MARINE...
Behind a cold front, westerly flow is increasing across the lakes
today. This will result in small craft advisory worthy winds up to
25 knots on the lakes today, with gusty winds also across portions
of the major rivers.

Small craft conditions will then continue into the weekend on both
lakes Erie and Ontario as low pressure moves very slowly east across
Quebec, producing moderate west to northwest winds on the Lower
Great Lakes.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...Lake Effect Snow Warning from 6 AM Thursday to 6 AM EST Friday
     for NYZ007-008.
     Lake Effect Snow Warning from 6 AM Thursday to 6 AM EST
     Saturday for NYZ006-012-019-020-085.
     Lake Effect Snow Watch from Thursday evening through late
     Friday night for NYZ003>005.
MARINE...Small Craft Advisory until 7 PM EST this evening for LEZ020.
         Small Craft Advisory until 7 PM EST Friday for LEZ040-041.
         Small Craft Advisory until 7 AM EST Saturday for
         LOZ042>045.
         Small Craft Advisory until 7 PM EST this evening for
         SLZ022.

&&

$$

SYNOPSIS...CHURCH/THOMAS
NEAR TERM...CHURCH
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...CHURCH
MARINE...CHURCH/THOMAS



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