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FXUS61 KBUF 121455
AFDBUF

Area Forecast Discussion
National Weather Service Buffalo NY
955 AM EST Wed Dec 12 2018

.SYNOPSIS...
Weak high pressure will allow for a brief period of dry weather into
this evening, a passing disturbance will then bring light snow to
areas south of Lake Ontario tonight and early Thursday. Much warmer
air will reach our region Friday and through the weekend, with
temperatures topping out into the 40s each day.

&&

.NEAR TERM /THROUGH TONIGHT/...
Moisture in the lower levels will maintain a cloudy day across the
region as an upper level ridge axis nears, creating a subsidence
inversion that will make it difficult in eroding these clouds.
The North Country will have the best chance of clearing within a
northwest flow keeping the addition of lake moisture to a
minimum. This clearing will allow for the North Country to
quickly cool this evening, supporting overnight lows that will
dip down into the lower to mid single digits.

This upper level ridge will give us a brief period of dry weather
through the afternoon and early evening hours. Water Vapor imagery
this morning showing a potent shortwave trough moving into the
western Great Lakes that will near our region tonight. Moisture
pooling ahead of this feature, combined with lift associated with
the shortwave will bring a period of light snow across our region
tonight, mainly south of Lake Ontario. Snowfall rates will be
modest, up to a half inch per hour, that in total could yield 2 to 3
inches of snow tonight across the hills of the Southern Tier, with
an inch or two of snow just to the south of Buffalo and Rochester.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY NIGHT/...
A mid level circulation that will be centered over our forecast area
at the start of this period Thursday morning will open up and exit
to our east during the course of the midday and afternoon. Leftover
snow showers associated with this compact mid level feature will
taper off in the process...with significant hgt rises and tons of
subsidence promoting fair dry weather for the second half of the
day. A portion of the downward motion will be supplied by being in
the proximity of the left rear entrance region of a 100kt H25 over
the Mid Atlantic region. Unfortunately...there may still be enough
low level moisture in place to keep us from completely clearing off.

A burgeoning ridge will be found over the Lower Great Lakes Thursday
night. The amplification of the ridge will be largely due to heights
being pumped up downstream from an anomalously deep storm system
over east Texas. This will guarantee fair dry weather across our
region Thursday night...with strengthening warm advection taking the
chill off the string of cold nights. In fact...low temperatures east
of Lake Ontario will be some 20 degrees higher than those from the
previous night.

Speaking of rising temperature trends...the mercury will climb into
the 40s across the region on Friday...as weak warm advection will
continue within a split mid level flow. This will include a
progressive trough that will dig across the Upper Great Lakes...
while an impressive stacked low will churn across the Lower
Mississippi Valley. We will be wedged between these two systems
where will still be able to cling to the backside of an Atlantic
ridge. This will leave us 'high and dry' on a day that looked much
more pessimistic earlier in the week. The exception will be across
the northern portions of Jefferson County/Thousand Islands region
where there will be a low chc for some rain showers in the
afternoon. Otherwise...the day will just feature thickening clouds.

The split flow will remain separate Friday night with the trough in
the arctic branch of the jet passing just to our north...while the
expansive and mature southern storm will actually start to weaken
with a broadening of its surface low. This will leave general
troughiness over our region...but nothing synoptically to really
focus or force significant pcpn. There will be an increase in
Atlantic moisture though...as a stronger south to southeast flow
will direct a deeper moisture field northward across eastern
Pennsylvania into New York state. The guidance packages during the
past several days have been at odds in handling the evolution of
this non-phasing event...but they seem to be aligning much better...
at least through this night and Saturday. In any case...the deeper
moisture and generally weak lift provided by an upper level jet will
help to support some rain...especially east and south of the Genesee
Valley where a 40kt low level jet could come into play. Rainfall
amounts through the night are not expected to exceed a quarter inch.

Have continued the trend of lowering the pops for Saturday...as
there is stronger consensus among the guidance packages that the
bulk of the moisture will push east of our region. Synoptically...
the northern trough will exit across New England while the closed
off storm system over the Deep South will slow its eastward
progress. This SHOULD allow for ridging to extend from the Plains to
the Great Lakes region...essentially creating a Rex block over the
Ohio Valley. Since we will be on the north side of this block...we
should be able to experience improving conditions throughout the
day with only some leftover morning showers for sites south of a
line from KBUF to KROC to KART.

The semblance of a Rex block will become a little better organized
Saturday night as ridging will continue to build across the Lower
Great Lakes. This should enable our region to have a fair dry night
although am not promising substantial clearing...just yet.

&&

.LONG TERM /SUNDAY THROUGH TUESDAY/...
We can anticipate a gradual lowering of temperatures during this
period...and contrary to the 00z GFS and many of its related GEFS
ensemble members...the majority of the period should be pcpn free.

On Sunday...a digging long wave trough over Ontario should pinch the
extension of a ridge that will be over our forecast area while the
decaying southern stream storm system will head for the Carolina
coast. This scenario would support fair dry weather for our region
through Sunday night.

The digging trough will push a somewhat moisture starved cold front
across our area on Monday. This should support scattered nuisance
snow showers...although the 00z operational GFS is depicting a much
more aggressive and robust shortwave that would result in widespread
accumulating snows. This is clearly an outlier from the majority of
the GEFS ensembles and certainly from the ECMWF...which has been the
more consistent and meteorologically realistic model leading up to
this point. Will thus only carry low chc pops for snow showers.

High pressure will build across the Lower Great Lakes in the wake of
the front Monday night and Tuesday...promoting a return to dry
weather as we progress deeper into the new work week.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
Widespread MVFR ceilings across the region late this morning, with
widespread vsbys of 3-5SM in fog.

Improvement through this afternoon will likely be slow with low level
moisture trapped underneath a subsidence inversion, as an upper
level ridge axis passes across the region. Most areas south of
Lake Ontario will likely remain with MVFR ceilings with
eventual improvement in vsbys. KART will likely see the lower
cloud deck erode from the northeast through early to mid
afternoon.

Any improvement in flight conditions through this afternoon will
again lower tonight as an upper level disturbance passes just to the
south of the region, spreading light snow across areas south of Lake
Ontario. KJHW will likely diminish to IFR just before 06Z, with
MVFR, brief IFR farther to the north across KBUF/KIAG and KROC after
06Z.

Outlook...

Thursday...Mainly VFR with a chance of light snow showers.

Friday...Mainly VFR with a chance of rain showers across
the Southern Tier.

Saturday and Sunday...VFR/MVFR with a chance of rain showers.

&&

.MARINE...
Between a surface high over northern New England, and surface low
over the Midwest, an easterly flow will develop this afternoon and
tonight on the lakes with wind speeds exceeding 20 knots on the
western end of Lake Ontario. Associated small craft advisories
are outlined below for the western half of Lake Ontario.

Winds will veer to southeasterly tomorrow and weaken with lowering
wave heights pushed towards the Canadian waters.

The southeast to south winds will remain on the lakes Thursday
through Friday night, but likely remaining just below small
craft thresholds. Another storm system will near the region for
the weekend, though north winds associated with this system may
remain light enough to continue favorable boating conditions.

&&

.BUF WATCHES/WARNINGS/ADVISORIES...
NY...None.
MARINE...Small Craft Advisory from 7 PM this evening to 7 AM EST
Thursday for LOZ042-043.

&&

$$

SYNOPSIS...Thomas/TMA
NEAR TERM...Thomas/TMA
SHORT TERM...RSH
LONG TERM...RSH
AVIATION...Thomas/TMA
MARINE...Thomas/TMA
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