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Area forecast discussion
National Weather Service Buffalo New York
605 am EST Wed Nov 20 2019

Synopsis...
a weak upper level disturbance will cross the eastern Great Lakes
through this afternoon, producing a few light rain and snow showers.
Dry weather will return tonight and Thursday as high pressure builds
into the area. A cold front will then cross the region Thursday
night and Friday, producing a few rain showers and breezy conditions.

&&

Near term /through tonight/...
a weak upper level trough makes its way across the region through
this evening before heights begin to rise late tonight. This
trough is characterized by limited cold air (h85 temps only as
low as -4c) and little in way of deeper moisture. So, even
though there is a weak sfc trough working across this morning
from north to south switching winds more to NW, support for much
more than a few showers, mainly in form of rain, is minimal as
there will be little if any help off the lakes (lake sfc temps
45f/7c only gives Delta T/S of 11-12c).

If it were colder this morning, think there would be more of a
concern for slippery spots, but the clouds overnight have helped
temps most areas stay into the middle 30s. New York state thruway data, which
yesterday morning showed some Road surface temps in the upper 20s to
near 30, is indicating Road surface temps in the mid to upper 30s
this morning. Still, could see some isolated slippery spots in the
higher terrain of the southern tier early today where there is some
fog noted (though not seeing vsby as low as yesterday morning). Also
could see some slippery spots east of Lake Ontario where temps fell
into the 20s before clouds moved back overhead.

Generally, seems that better chances for precip through the
afternoon will be over the higher terrain south of Buffalo/into the
southern tier and on east to The Finger lakes as the NW winds
provide some upslope lifting. Even here though, only looking at low
end chances and that is probably generous. Tonight, greater moisture
up to 800 mb/5kft shifts toward Finger Lakes and low-level convergence
is strongest there as well. So, that is where few light rain
showers/drizzle should move to through the night before diminishing
late. Elsewhere, high pressure ridge begins to arrive from the west,
but skies will stay mainly cloudy. Low temperatures tonight will be
in the low to mid 30s with some upper 20s over higher terrain of
southern tier. Where any clearing occurs it would open door up for
potential for patchy fog.

&&

Short term /Thursday through Saturday/...
on Thursday...surface high pressure draped squarely across our
region at the start of the day will slowly drift eastward to the New
England coastline...while a deepening area of low pressure tracks
from the upper Mississippi Valley to the Michigan straits. The
resulting warm air advection pattern in between these two systems
will result in a milder day with temperatures climbing into the mid
to upper 40s across the bulk of the area...along with some partial
early morning sunshine giving way to increasing cloud cover from
west to east through the rest of the day. The above said...the
approaching low should remain far enough to our north and west to
result in a mainly dry day...with just the low-end chance of a
shower or two reaching far western New York toward sunset.

Thursday night and Friday the deepening surface low will continue
its northeastward trek across Ontario and Quebec provinces...and
in the process will sweep its trailing cold front across our area
between late Thursday night and Friday morning...with the approach
and passage of this boundary helping to generate a round of fairly
numerous to widespread rain showers. Following the passage of the
front...increasing drying and subsidence will then result in the
showers becoming considerably more scattered from west to east
through the balance of the day...while mixing with some wet snow
Friday afternoon as cold air advection increases on the backside of
the system. All the above stated...total precipitation amounts with
this system look to remain low and on the order of a tenth to a
quarter of an inch in most locations...and this combined with the
diminishing nature of the precip during the transition in ptype will
help to greatly limit any snowfall accumulations to only minor
amounts... with these mainly confined to the higher terrain east of
Lake Ontario.

While precipitation will thus not be much of a concern with this
system...its associated winds could potentially be a different
story. While the 00z/20 suite of guidance continues to show quite a
bit of variance with the overall strength and track of the low...
and the GFS remains much stronger and closer to our area with its
track compared to the other models...in general the guidance seems
to be trending a bit stronger overall with this system...with this
trend most noticeable in the 00z European model (ecmwf) and Gem. While there is still
quite a bit of uncertainty...the overall pattern and lingering 40-50
knot flow aloft behind the cold front would seem to suggest at least
some potential for a round of fairly windy conditions following the
cold frontal passage later Thursday night and Friday...with this
greatest over and east of Lake Ontario.

Otherwise...rather mild temperatures in the 40s out ahead of the
cold front Thursday night will give way to falling readings
following its passage late Thursday night and early Friday...with
all areas seeing readings tumbling into the lower to mid 30s by
later Friday afternoon.

During Friday night surface high pressure and much drier air will
build across our region...with the dry nature of the incoming
airmass and rather low inversion heights conspiring to keep any lake
response over and southeast of the lakes rather meager in nature.
Meanwhile...the combined effects of cold advection and nocturnal
cooling will help to send temperatures down into the lower to mid
20s across the north country...and to the mid to upper 20s
elsewhere.

On Saturday the surface high will only begrudgingly drift eastward
to New England...while a southern stream trough and associated
modest wave of low pressure develops into the Ohio Valley. While
this latter system should draw close enough to spread some clouds
into our region Saturday afternoon...the departing ridging should
remain dominant enough to result in a mainly dry day...with only an
outside chance of a rain/snow shower reaching the southern tier
late. Otherwise...we can expect somewhat below average high temps
ranging from the mid-upper 30s east of Lake Ontario to the upper 30s
and lower 40s elsewhere.

&&

Long term /Saturday night through Tuesday/...
Saturday night and Sunday the GFS and European model (ecmwf) have come into somewhat
better agreement on lifting the aforementioned trough and surface
low northeastward from the Ohio Valley...with secondary cyclogenesis
taking place along the mid-Atlantic coastline...and the ensuing
coastal system then tracking northeastward along the New England
coast. Such an evolution in the pattern would result in a potential
for some light rain or snow showers as this system traverses our
region between Saturday night and Sunday. Meanwhile...the Gem has
the same general idea save that it keeps everything suppressed much
further to the south...which would keep dry weather intact across
our region until Sunday...when the latter model subsequently swings
a weak northern stream trough across our area. Taking the increasing
agreement between the GFS and European model (ecmwf) into consideration along with
the differing Gem solution and our previous continuity of a mainly
dry forecast...for now have elected to bump pops up just into the
lower portion of the chance range for Saturday night and Sunday.

Following the passage of this next potential system...high pressure
and drier air still looks to build eastward across our region Sunday
night and Monday...before drifting eastward to New England on
Tuesday. Coupled with unimpressively cool temperatures aloft...this
would likely help to keep any lake response in the wake of the low
rather minimal Sunday night and early Monday...with mainly dry
weather otherwise prevailing through the remainder of the period.

With respect to temperatures...somewhat below average readings at
the start of the period should give way to a warming trend for
Monday and especially Tuesday as the axis of the ridge slides off to
our east...when the ensuing warm advection regime should help to
push readings back above late November normals.

&&

Aviation /11z Wednesday through Sunday/...
expect stratus clouds to persist through the period, though clouds
may clear out at Art later tonight. A few rain showers, possibly
mixed with snow, may occur today over western New York to The Finger
lakes, but these will be few and far between in coverage and
certainly not enough to include in these tafs.

Cigs for most part will reside in the MVFR to lower VFR category.
Lower exception could occur at jhw where IFR cigs and some fog may
occur at times through this afternoon. For tonight where skies
remain mostly cloudy, expect a continuation of MVFR to lower VFR
range cigs.

Outlook...
Thursday...mainly VFR with a chance of showers Thursday
night.
Friday...MVFR/VFR with a chance of showers. Breezy.
Saturday and Sunday...mainly VFR.

&&

Marine...
a weak pressure gradient will remain in place across the eastern
Great Lakes through Thursday morning, with winds generally 15 knots
or less and waves under 3 feet. A moderately strong area of low
pressure will then move from the upper Great Lakes Thursday
afternoon to southern Quebec by Friday, with a trailing cold front
crossing the eastern Great Lakes Friday morning. Southerly winds
will increase ahead of this system later Thursday afternoon and
Thursday night, then become southwest on Friday following the cold
front. Looks very likely that small craft advisories will be needed
Thursday night into Friday and there is certainly a chance that gale
headlines may be needed as well, especially Friday on Lake Ontario.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...Hitchcock
near term...jla

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