Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
1133 PM EST Monday Dec 22 2014
a weak low pressure system will move up the East Coast tonight while
another low moves into the central Great Lakes region Tuesday. Both
will have the potential to bring some light showers to portions of
the state. Then...a much stronger system will move up the
Mississippi Valley and into the central Great Lakes region on
Wednesday...with all of western and central New York seeing rain
under an unseasonably warm airmass. A cold front will arrive for
Christmas day with strong winds...followed by some more rain and
eventual snow showers over the region but with little if any
Near term /through Tuesday/...
regional radar imagery continues to show a broad area of showers
moving into ctrl New York out of PA...the result of shortwave energy
ejecting out of the Ohio Valley into an area of broad isentropic
uplift with a dose of Atlantic moisture for good measure. While the
bulk of these showers are focused across ctrl New York...a few isolated
showers are also crossing into portions of the western southern tier
where surface temperatures continue to hover just below freezing.
This is resulting in isolated pockets of freezing rain. Given how
isolated the precipitation is and the fact that temperatures will be
warming above freezing overnight...have opted to go with a Special
Weather Statement to highlight the isolated threat. The showers will
continue to track north and east across The Finger lakes and lake
plains where temperatures are well above freezing. Temperatures in
the north country are currently near or above freezing at this
point...however there remain a few isolated pockets of sub-freezing
air across the St. Lawrence Valley and an Special Weather Statement may be needed later
tonight as showers edge closer to the area.
Regarding temperatures...broad warm advection will be taking place across the
forecast area tonight and temperatures will reflect this trend with
early evening lows in the low/middle 30s giving way to middle/upper 30s by
sunrise. Any lingering showers should also be in the process of
moving out of the north country around daybreak as the shortwave
lifts across the Ottawa/St. Lawrence valleys...giving way to what be
a mainly dry morning across the area. With large scale warm
advection/isentropic uplift ongoing across the region...expect
plenty of cloud cover to remain across the area throughout the day
however with a chance of showers returning by the afternoon as
another middle-level shortwave swings across the region. Warm advection
will push temperatures into the middle to upper 40s by the afternoon
Short term /Tuesday night through Thursday night/...
persistent low/middle level warm advection and upper level divergence
Tuesday night will continue to produce a wealth of cloud cover and
at least a few scattered showers. The initial series of weak lead
middle level shortwaves will lift into Quebec overnight with any
organized showers following. Toward Wednesday morning a renewed push
of stronger warm advection will move into the western southern tier
with showers becoming more widespread. It will remain quite mild
with lows in the lower to middle 40s in most areas. These lows are
likely to occur early...with temperatures becoming even warmer by
On Wednesday a strong push of warm advection and upper level
divergence will produce a periods of rain across the entire region.
The broad area of ascent will be enhanced by several middle level
vorticity maxima crossing the region downstream of the main middle
level trough. A plume of deep moisture will be captured and spread
northward by this system with precipitable water rising to around 1.25
inches...which is over 3 Standard deviations above average and near
the maximum observed for late December. Despite the copious amounts of
moisture...it does not appear there will be enough of a focus within
the broad warm advection regime to produce excessive rainfall in any
one location. Maximum rainfall amounts should focus in areas favored by
upslope southerly flow...such as the southern Tug Hill plateau where
rain amounts may exceed 1 inch. Elsewhere expect around a half inch
total across lower elevations and 3/4 inch across the higher terrain
of the southern tier and Finger Lakes.
Wednesday night a strong cold front will cross the region and
produce one last period of rain forced by strong middle level height
falls and low level convergence along the frontal zone. The
showalter index drops to just below zero along the front...so there
may even be a few scattered thunderstorms. Given the very strong
wind field associated with the system any thunderstorm that does
form may produce gusty winds. Rain will quickly end from west to
east overnight with the passage of the surface cold front...with a
notable middle level dry slot crossing the region immediately behind
The main concern with this system continues to revolve around wind
with some potential for damaging winds northeast of lakes Erie and
Ontario. A surface low will rapidly deepen as it moves from the
lower Ohio Valley across Michigan late Wednesday before reaching
western Quebec by Christmas morning. This is a climatologically
favored track to produce strong winds northeast of lakes Erie and
Ontario where winds are channelled by the lakes and terrain. The
latest GFS continues to support a moderate intrusion of
stratospheric air with the dynamic tropopause folding down to around
500mb...suggestive of deeper middle level instability and mixing in the
dry slot behind the cold front. The best isallobaric fall/rise
couplet is still forecast to pass through the Central Lakes...but
moderate pressure rises on Thursday will still aid in downward
Model guidance continues to show some run to run variance with
respect to the exact track and strength of the low...and also a good
deal of run to run differences with wind speeds aloft. The latest
12z GFS trended a little faster and slightly weaker with the surface
low and notably weaker with winds aloft...although probably still
just strong enough to produce 45-50 knot gusts northeast of the
lakes. Given that this is still almost 3 days away and we are still
seeing run to run model differences...will hold off on a high wind
watch for now. It appears the strongest winds will occur from later
Wednesday night through the first half of Christmas day across
western New York northeast of Lake Erie...and a few hours later northeast
of Lake Ontario.
Otherwise on Christmas day a brief period of wrap around moisture
will cross the lower lakes. There is a distinct lack of cold air
behind this system with 850mb temperatures only dropping to around -6c by
the end of the day. This will only support a few wet snowflakes
mixing in with the rain at lower elevations...with higher terrain
probably changing over to all wet snow. Could see some minor less
than an inch accumulations on the hills...with no accumulation
across lower elevations. It is not even close to cold enough for any
lake response. Temperatures will start off in the 40s in most areas
at daybreak then fall into the middle to upper 30s through the day. It
will not be a white Christmas this year in western New York.
Any lingering light snow showers east of the lakes Christmas evening
will end overnight as a ridge of high pressure builds towards the
lower lakes and any remaining moisture is stripped away.
Long term /Friday through Monday/...
on Friday high pressure will build through the middle Atlantic with a
ridge extending north into the lower lakes and providing a dry day
with even a good chance at some sunshine. What little cool air
briefly enters the region on Christmas day will be gone as warm
advection brings 850mb temperatures to around +2c. This will support highs
back into the 40s...a good 10 degrees above average. On Saturday a
fast moving middle level trough will swing through the Great Lakes and
Quebec. This may produce a few rain showers mixing with wet snow
later in the day as moderate cold advection begins. It may become
marginally cold enough for some limited lake effect by Saturday
night east of the lakes.
Models diverge significantly by Sunday. The 12z European model (ecmwf) remains
consistent with previous runs in taking a strong southern stream
trough through the Ohio Valley and into the northeast...with a
frontal wave spreading a band of accumulating snow across our
region. The GFS remains consistent with its previous runs in keeping
any semblance of this wave suppressed far to the southeast with a
weak wave running through the southeast states. The Canadian Gem is
closer to the European model (ecmwf) solution through Saturday. For now will hedge
towards the European model (ecmwf) scenario and place a chance of snow into the
forecast for Sunday and Sunday night. Both the GFS and European model (ecmwf) then
suggest a mainly dry Monday as high pressure builds into the
Aviation /06z Tuesday through Saturday/...
VFR ceilings across the forecast area will lower to MVFR across portions
of ctrl/nctrl New York by 06z as increasing low-level moisture and lift
arrive from the south. An area of -shra moving north out of PA will
accompany these lower ceilings with a few isolated areas of
ip/-fzra...mainly across higher terrain of the southern tier and the
north country developing briefly before changing over to -shra as
warmer air surges northwards across the area. Any freezing precipitation is
not expected to impact forecast terminals.
The upper level disturbance that will be aiding in the development
of the precipitation across the area tonight will lift off to the northeast
across the St. Lawrence Valley late tonight with precipitation tapering off
across the north country after 12z. Otherwise any lingering MVFR
ceilings will improve to VFR ceilings Tuesday morning...mainly after 10-12z.
Wednesday...mostly MVFR and some -shra. Some gusty winds.
Wednesday night...MVFR/IFR with -shra.
Thursday...MVFR with -shra/-shsn and gusty/strong winds.
Saturday...possible MVFR conditions with scattered shsn.
a weak low will move up the East Coast tonight and fall apart while
a second low moves into the central Great Lake region and similarly
weakens on Tuesday. On Wednesday...a much stronger and deepening
system will move up the MS valley and into the central Great
Lakes...with small craft and eventually gale fore potential winds
late Wednesday night and Thursday over Lake Erie. Gale force winds
are also possible on Lake Ontario later Thursday.
Marine...gale watch from late Wednesday night through Thursday
afternoon for lez040-041.