Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
1153 PM EST Wednesday Nov 26 2014
a Nor'easter will lift along the Atlantic coastline. Snow will
taper off this evening from west to east...though some limited
lake enhanced activity will lingering into Thanksgiving
morning...especially southeast of Lake Ontario. Then another
disturbance will cross the region Thursday night...bringing more
light lake effect snow showers.
Near term /through Thursday/...
a coastal low centered near Cape Cod will continue to lift
northeastward across the Gulf of Maine tonight. Most of the
precipitation wrapped around this low has already exited to the
east...with just light snow lingering east of Lake Ontario late
After this...our attention turns to the potential for lake
enhanced snow showers overnight. 850mb temperatures are forecast to
drop modestly down to about -10c through daybreak which will
result in small values of lake induced instability. However...with
a fairly moist boundary layer this should be enough for some light
lake effect snow south of the lakes. A blend of high resolution
guidance (nam/rgem/hrrr/WRF/arw) are pretty consistent in
forecasting light quantitative precipitation forecast south of Lake Ontario from Rochester to
Fulton. This would take advantage the longer fetch across Eastern
Lake Ontario...and possibly a subtle convergence zone.
Accumulations should generally be light with lake effect expected
to be multi-banded and generally disorganized...but local amounts
up to 2 inches are possible tonight...and again on Thursday. This
would include eastern Monroe County...Wayne...and northern Cayuga
counties. The only real chance for higher (advisory amounts)
would be if snow has a significant fluff factor...or if steadier
snows focus on one location for a long time.
Elsewhere...expect little if any accumulation...with snow
flurries further away from the lake. High resolution guidance
(hrrr in particular) has picked up on a convergence boundary Down
Lake Erie...but with a northeast flow this will largely focus
south and west of our region. Some light snow may meander onshore
in Chautauqua County (maybe an inch or so)...but otherwise expect only
light snow overnight and into Thursday morning.
An upper level shortwave crossing from the central Great Lakes to
the eastern Great Lakes through the day tomorrow may bring light
snow again into western New York by the end of the afternoon.
Temperatures will average a several degrees below normal this period.
Clouds should result in a minimal diurnal range. Lows tonight will
range through the 20s and highs tomorrow will average in the lower
Short term /Thursday night through Saturday/...
the latest surge of Arctic air will bring a renewed threat for
accumulating lake effect snows Thursday night and into Friday to
favored northwest flow areas...especially off Lake Erie where a
better aligned low level flow will exist.
Although over-lake instability will not be overly impressive with
Delta T/S around 15c...lake induced equilibrium levels look to rise
to over 10k feet for a time Thursday night. This may allow for
localized accumulations of 2-4" along the Chautauqua ridge.
Friday...cold air advection will continue on a northwest flow which
should maintain some multiple lake bands southeast of the lakes
early in the day. These bands should wane through the day as the low
level flow backs and influx of dry air and lower inversion heights
help to diminish the lake activity.
Friday night and Saturday...strong warm advection and isentropic
ascent develops as a clipper system works across the region. Models
suggesting a sharp increase in low level moisture signaling
widespread snow will develop across the region during this period.
The strengthening of the warm air advection and moisture surge
should be able to produce at least a couple inches of accumulating
snow. How much snow falls will be dependent on the amount of
moisture and warm air being brought into the region...but at this
time there is no reason to believe there will be anything more than
Long term /Saturday night through Wednesday/...
solid warm up still looks on track for Sunday in wake of a warm
frontal passage. 925 mb temperatures look to rise to near
+10c...which should support highs for most areas in the lower to middle
50s. Does not appear to be any real forcing mechanism for
precipitation within the warm sector other than weak isentropic lift
with broad warm air advection. This warm up appears short-lived as a
round of upper Midwest to Great Lakes height falls will force a cold
front south across the area late Sunday night into Monday. Band of
showers preceding the front likely holding off until Sunday
night...possibly ending as a bit of light snow as colder air spreads
into the region behind the front. Any lake effect which can
materialize Monday should end by Monday night as subsidence and
surface ridging move into western New York. High pressure will
provide a fair weather day Tuesday...before warm air advection
precipitation breaks out as strengthening return flow sets up behind
the departing high.
Aviation /06z Thursday through Monday/...
for the 06z taf cycle...a weak northerly flow is still resulting
in persistent clouds near or just below 3k feet south of the lakes
and including all but the Art taf site. Lower moisture is trapped
across the southern tier...with IFR ceilings at jhw.
Expect jhw to vary between IFR/MVFR overnight as low ceilings
periodically scatter out. Middle-level clouds lifting from light snow shower NE to
enhance lake effect snow off of Lake Ontario...which may lower roc
to IFR in snow/cigs. Forecast confidence remains low for roc.
Elsewhere...expect ceilings around 3k feet overnight.
On Thursday...expect ceilings improve somewhat...with mostly VFR
conditions by mid-day. Periodically lower conditions are possible
in lake enhanced snow showers and clouds. A shortwave will bring a
period of steady snow showers Thursday evening from west-east with IFR
or MVFR conditions likely.
Thursday night...mainly VFR with a chance of MVFR in snow
Friday...mainly VFR with a chance of snow showers/MVFR.
Saturday through Monday...mainly VFR with a chance of rain and
a developing storm system will lift northeastward along the Atlantic
coastline tonight. Have issued a brief Small Craft Advisory for the southeastern
shores of Lake Ontario based on NE winds in the 15 to 20 knots range
which are likely to build waves up to 5 feet. This will be short
lived as winds diminish late tonight.
In the wake of this system...a secondary surface trough will then
cross the lower lakes region later Thursday and Thursday night...and
will likely be accompanied by a period of advisory-level westerlies
and attendant higher waves.
after an extended period of cold during the middle of November it
appears temperatures will average above normal most of the time over
the next few weeks. There will be brief pushes of colder air at
times as progressive troughs amplify into the Great Lakes...but
these cold periods will be short lived...only lasting for a few days
at a time...and will be outnumbered by mild days.
Looking at the hemispheric pattern...a positive North Atlantic
oscillation /nao/ will persist into the first few days of December
based on the gefs ensemble mean. The mean longwave trough over the
North Atlantic in such a pattern will prevent any cold from locking
in over the northeast quarter of the United States. The Pacific
North American pattern /pna/ will remain negative through the first
few days of December...before trending positive based on gefs
ensemble members. This too will prevent cold from locking into the
northeast for more than a few days at a time.
The Madden Julian oscillation /mjo/ may play an important role in
driving pattern change through middle December. Analysis over the past
week has shown a moderately strong mjo event developing over the
Indian Ocean. A gefs ensemble forecast of the Wheeler phase/space
plot shows this mjo orbiting through phase 4 and 5 during the first
week in December as convection moves east across the maritime
continent. A look at composite charts of past events favors above
normal temperatures across much of the central and eastern United
States during phase 4 through 6 of the mjo.
Eventually as we get into the second week in December mjo convection
will continue its eastward orbit through the Pacific and into the
western hemisphere. If the mjo convection persists on its eastward
journey and reaches phase 7 of the Wheeler phase/space plot...it
would favor a significant pattern change towards colder than normal
temperatures over the central and eastern United States. The mjo
accomplishes this as sub-tropical convection influences the pattern
over the Pacific...forcing amplification of the eastward extension
of the east Asian jet which in turn forces downstream amplification
of the pattern across North America. Based on the forecast timing of
the mjo episode this would most likely occur by week 2 or 3 of
December and feed back into more high latitude blocking and more
long lasting cold.
Marine...Small Craft Advisory until 4 am EST Thursday for loz043-044.