Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
636 PM EST Wednesday Dec 4 2013
deepening low pressure over Wisconsin will lift across the western
Great Lakes tonight...then across eastern Ontario on Thursday when
it will swing its associated cold front across our region. In
advance of the front...unseasonably mild conditions will remain in
place across western and north central New York through much of
Thursday. We can then expect a return to much colder weather with
featuring below normal temperatures for Friday through the upcoming
Near term /through Thursday/...
low pressure over Wisconsin this evening will lift northeastward
across the upper Great Lakes overnight...then on to James Bay on
Thursday. In the process...this system will keep a southwesterly
flow of unseasonably mild air across our region before swinging its
trailing cold front across New York state Thursday afternoon and
Tonight...expect generally dry weather to persist through most of
this evening...though there will be an increase in cloud cover once
again as yet another surge of warm air advection will overspread
our region. After that...a strengthening low level jet segment and
middle-level shortwave will ripple northeastward within the deep
southwesterly flow aloft...and should help to augment the background
warm advective lift just enough to generate a round of scattered
light rain showers. At this point...the best chances for these
appear to be from the counties along the South Shore of Lake Ontario
northward...with somewhat lower probabilities found further to the
south given weaker overall synoptic scale forcing. Otherwise...the
combination of the increasingly mild airmass and a strengthening
southerly low level flow will result in nighttime lows that will be
well above seasonal averages...as well as a non-diurnal temperature
trend with readings generally bottoming out this evening...then
slowly rising overnight. Expect lows to range from the middle to upper
30s across the north country...to as high as the middle and upper 40s
along the lake plains of far western New York where increasing
downsloping effects will also come into play. Speaking of which...
these will probably also result in increasingly windy conditions
along the Lake Erie shoreline south of Buffalo...where sustained
winds of 20-30 miles per hour with gusts to 40 miles per hour or so appear to be a
distinct possibility during the late evening and overnight hours.
On Thursday...the aforementioned cold front will approach our area
during the morning...before slowly crossing New York state during
the afternoon and evening as a weak secondary wave of low pressure
develops and rides northeastward along the frontal boundary. Coupled
together...these two features will help force the development of
another round of more numerous showers between the late morning and
afternoon hours...with the 12z guidance suite in good agreement on
focusing the bulk of these from the southern tier northeastward
across The Finger lakes and north country...while keeping more
scattered activity across portions of the Niagara Frontier. Given
both favorable lift and moisture...have bumped probability of precipitation across our
southern tier/Finger Lakes/north country zones to the high likely to
categorical range for Thursday afternoon...while keeping chance probability of precipitation
in play further to the north and west. Temperature-wise...the very
mild airmass and persistent southerly flow in advance of the front
will result in temperatures climbing to the middle to upper 50s in most
places by midday/early afternoon...before readings begin to drop off
a bit across far western New York Thursday afternoon following the
Short term /Thursday night through Saturday night/...
Thursday night a cold front will move southeast across the region.
As it does so...a weak wave of low pressure will run northeast along
the boundary. This will increase differential thermal advection
across the boundary with frontogenetic forcing and upper level
divergence bringing increasing chances of precipitation overnight. The
greatest amounts will be found across the southeast portion of the
area from the southern tier through The Finger lakes to central
New York...with much lesser amounts near the Canadian border.
Precipitation type will be difficult...as low level cold advection
undercuts the frontal wave. In general expect rain to slowly turn to
wet snow late Thursday night from northwest to southeast...but with
the cold air undercutting the frontal wave there may be a brief
period of sleet or freezing rain during the transition mainly from
the southern tier into The Finger lakes. Snow amounts will be
relatively light...with an inch or so on the hills of the southern
tier and less than an inch elsewhere. The lower elevations of
central New York will be last to changeover...so expect mainly rain there
with no accumulation.
On Friday the first frontal wave will move off into New England.
This should allow precipitation to end in most areas...with the possible
exception of the southern tier which may remain close enough to the
frontal zone to allow a few light rain and snow showers to continue.
Otherwise for the rest of the area expect a good amount of middle and
high clouds to the north of the front. Temperatures will be back
close to average with middle to upper 30s at most locations.
Friday night another frontal wave is a possibility...although model
guidance is still in poor agreement with respect to the amplitude
and track of this wave. The NAM...ECMWF...and sref mean are a little
farther north with this feature while the latest 12z GFS is more
suppressed and weaker. Favor the somewhat farther north model
consensus for now given run to run inconsistency seen in the GFS
during this time period. If the farther north solution verifies
there will be a period of light snow Friday night...especially
across the southern tier and Finger Lakes with some minor
By Saturday morning this next frontal wave will be exiting into New
England. Cold advection behind the wave will bring temperatures down
enough to support some limited lake response...but a very dry
background environment...anticyclonic curvature in the low levels...
and an overall unfavorable synoptic setting will greatly limit this
potential. Expect just a few flurries or light snow showers
southeast of Lake Erie on Saturday. East and southeast of Lake
Ontario may be marginally more favorable...but still only expect a
few light snow showers.
Long term /Sunday through Wednesday/...
Sunday will start off dry with high pressure briefly cresting over
the lower lakes in the morning. Our attention quickly turns to the
next system as a strong middle level shortwave ejects out of the
western trough. A weak associated surface low will develop over the
lower Ohio Valley Sunday night then track through the Central Lakes
on Monday. This track will allow a brief push of warmer air to move
into our region later Sunday night into Monday. This will result in
a mixed bag of precipitation...with light snow developing late
Sunday or Sunday evening then quickly changing to a wintry mix
Sunday night...then eventually to just rain by Monday. Snow and
mixed precipitation amounts look relatively minor...so while this may
produce some tricky travel for a few hours it will not be
Following this system it is looking more and more likely that at
least a piece of the frigid air building over the northern plains
will be drawn southeast and into the Great Lakes by the middle of
next week. This would bring temperatures well below average starting
as early as Tuesday and continuing through much of the week. The
synoptic pattern from Tuesday into at least midweek would also
suggest a better chance of organized lake effect snow east of the
lakes with cyclonic westerly flow developing. Stay tuned.
Aviation /00z Thursday through Monday/...
low pressure over Iowa will lift into Wisconsin by this evening...
then out across Ontario province tonight and Thursday...with its
trailing cold front crossing our region Thursday afternoon and
Through this evening...expect dry weather and VFR conditions to
continue to be the general rule...albeit with some increase in
clouds again this evening as another shot of warm air advection
develops into our region. Overnight...the ongoing warm air advection
pattern could generate some scattered light showers...but overall
conditions should remain VFR...except across the higher terrain of
the southern tier where some MVFR/localized IFR ceilings may redevelop
as a surge of Atlantic moisture lifts northward at the low levels.
Low level wind shear will also develop overnight as a 45 knots
southerly low level jet overspreads the region from west to
east...with this then expected to linger into Thursday morning
across western New York...and into early Thursday afternoon across
the north country.
During Thursday...expect scattered light showers to gradually become
more numerous just south and east of kbuf and kiag as the cold front
works into our region...and a weak secondary wave of low pressure
develops and rides northeast along the frontal boundary. This should
result in conditions eventually lowering to MVFR along and ahead of
the front during the late morning and afternoon hours...with some
Post-frontal MVFR ceilings also likely to impact kbuf/kiag for a time.
Thursday night...deterioration to MVFR/IFR with a period of rain and
Friday...VFR/MVFR with a chance of rain and snow showers.
Saturday...VFR/MVFR with a chance of snow showers southeast of the
Sunday...mainly VFR with a chance of snow in the afternoon south of
Sunday night and Monday...VFR/MVFR with a chance of snow and rain.
in the wake of a warm front...a strengthening southerly flow will
overspread the lower Great Lakes tonight. This southerly flow will
persist until a cold front crosses the region between late Thursday
morning and early Thursday evening...when winds will veer more
westerly and decrease somewhat. While the highest waves will remain
offshore and in Canadian waters given the prevailing southerly
flow...we still expect winds to reach advisory criteria across
Eastern Lake Erie and the eastern half of Lake Ontario tonight and
tomorrow...for which small craft advisories have been hoisted.
After this...westerly winds may briefly increase again across
Lake Ontario Thursday night...which could result in advisory-type
winds and waves persisting across that lake through the night. This
is not a sure bet however...so for now have held off on extending
the existing flags into/through Thursday night. Otherwise...expect
winds and waves to generally remain below advisory levels through
the end of the week as only a weak to modest pressure gradient will
be in place across the lower lakes region.
Marine...Small Craft Advisory from 10 PM this evening to 10 am EST
Thursday for lez040-041.
Small Craft Advisory from midnight tonight to 7 PM
EST Thursday for loz044-045.
Small Craft Advisory from midnight tonight to 4 PM EST
Thursday for loz043.