Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
453 am EDT sun Aug 31 2014
a slow moving trough of low pressure will produce occasional showers
and scattered thunderstorms across much of the region this morning
before slowly tapering off from northwest to southeast this
afternoon. It will remain muggy although extensive cloud cover will
keep temperatures lower than yesterday. A few spotty showers and
thunderstorms are possible on Labor Day...but the majority of the
day should be rain free with temperatures warming back to a little
Near term /through tonight/...
radar imagery early this morning showing a wide band of numerous
showers extending from Ohio into northwest PA and across much of
western and central New York. Lightning has been steadily decreasing with
just a few isolated strikes noted recently in some of the strongest
showers. Expect showers to remain in this general area through the
early morning hours.
For today a middle level trough will advance east across the central
Great Lakes...with downstream height falls and DPVA produced by
convectively augmented vorticity maxima aiding in large scale
ascent. Upper level divergence will be enhanced by the right
entrance region of a 80+ knot upper level jet stretching from lower
Michigan to southern Quebec. A belt of 30-35 knot flow in the
900-700mb layer will aid in organizing convergence and moisture
transport. At the surface weak/elongated low pressure will move into
southern Quebec with a weak pre-frontal trough easing across the
lower lakes providing low level convergence. Infrared satellite imagery
showing a weak baroclinic Leaf developing across the Ohio Valley
early this morning. As this feature translates northeast today it
will act to enhance middle level frontogenesis and deformation across
our region...aiding in more widespread showers. Precipitable water values are
around 1.8 inches on average with ample moisture in place.
Given the quality moisture and sufficient forcing for ascent coming
together...have raised probability of precipitation to categorical for the bulk of the area
this morning with the exception of a few counties along the Canadian
border where showers should be a little less frequent. In general
the most persistent rain and highest amounts should focus from the
western southern tier to The Finger lakes and southern Tug Hill
region with lesser amounts near the international border. Enough
instability will remain to keep a few embedded thunderstorms as
well...although coverage will remain widely scattered. A few storms
may produce locally heavy rainfall...but this risk should remain
very isolated at best.
This afternoon the aforementioned dynamics and baroclinic Leaf will
shift slowly south and east and take the steadier showers with it.
Expect a drying trend for the afternoon from northwest to southeast
with areas along and north of the New York state thruway eventually becoming
mainly dry with a few breaks of sunshine possible late. Showers will
be slower to end across the southern tier and across the higher
terrain east of Lake Ontario.
The extensive cloud cover will keep temperatures lower today
although it will still be very muggy. Expect highs in the upper 70s
on the lake plains and lower to middle 70s across the higher terrain.
The warm spot should be the Saint Lawrence valley where showers and
thicker cloud cover will exit the earliest.
Tonight showers across the southern tier and central New York will
continue to slowly diminish. Enough instability may develop in the
wake of this main rain area to allow scattered thunderstorms to form
during the late afternoon and early evening across the Niagara
peninsula. If they materialize...a few may make it into areas just
north of Buffalo this evening. Scattered storms may also form over
southeast Ontario and cross the Saint Lawrence into the north
country this evening. Otherwise expect some partial clearing
overnight on the lake plains. Across the higher terrain low level
moisture and weak upslope flow and convergence will likely support
expanding low cloud cover. Expect lows in the middle to upper 60s on
the lake plains and lower to middle 60s in the southern tier and north
Short term /Monday through Tuesday night/...
a warm and sticky airmass will remain across the region on
Monday...with most of the forecast area experiencing mainly dry
conditions. However there will be the chance for scattered showers
and thunderstorms in the afternoon and evening...mainly across the
interior southern tier where the best instability will reside. Cape
values by later in the afternoon across this region will run in the
1000-1500 j/kg range with lifted indice's possibly as low as -4. However with
weak 0-6km bulk shear (~20kts) and lack of a good surface trigger
(aside from a possible lake breeze)...not expecting any
thunderstorms to reach severe limits. Instability looks lower across
the remainder of the area...and thus convective chances look much
lower as well. Temperatures will again be on the warm side with
highs in the upper 70s to lower 80s.
With the loss of daytime heating Monday night most of the diurnally
driven convection will diminish in coverage...although a few storms
may continue late into the evening...especially across portions of
the southern tier. At the same time a cold front over the upper
Great Lakes will be advancing toward the region and be located west
of New York state by Tuesday morning. That said...most of the night
looks to remain dry...with precipitation chances starting to increase a bit
across western New York toward Tuesday morning. Another mild
night can be expected with lows in the middle to upper 60s for most
locations thanks to deep southerly flow out ahead of the approaching
Latest guidance package has the cold front now moving a bit slower
than in previous runs. This is most likely due to most of the models
now coming into agreement on the development of low pressure
somewhere in the Ohio Valley along the front and then tracking it
northeast along the boundary which would slow it down a little.
That said...it now appears it will take the bulk of the day Tuesday
for the cold front to sweep across the region with showers an
thunderstorms likely...with lower chance probability of precipitation by later in the day
across western New York. High precipitable water values of 1.7"-1.9"
Tuesday afternoon offer the risk of heavy downpours with any
thunderstorm. Sbcapes over 1000 j/kg combined with lifted index
values at -4c to -5c also point to the possibility of storms. The
main differences from Monday are that 0-6km bulk shear values look
to be in the 40-45kt range...and also have the surface cold front
crossing the forecast area which will serve as the Focal Point for
storms to fire along. All this said...looks as though there could be
some strong storms...with a few storms possibly reaching severe
limits. Main threats appear to be gusty winds associated with bowing
line segments and marginally severe hail. Another warm day on tap
with highs in the upper 70s to lower 80s.
The cold front will slide south and east of the forecast area
Tuesday evening...taking the showers and storms with it. Although a
few showers will still be possible during the evening across eastern
areas...but even here things will dry out later Tuesday night as
surface high pressure starts to build east across New York state.
Lows will be generally in the upper 50s to lower 60s.
Long term /Wednesday through Saturday/...
upper level ridging and surface high pressure will build across the
region Wednesday and Thursday bringing in drier air and temperatures
that will still average at or just a bit above normal for early
September. High pressure will then slide off the New England coast
by Friday. This will provide mainly dry conditions through
midweek...before the next frontal system approaches for late in the
week and early weekend. Temperatures will be a bit above seasonal
normals with highs in the upper 70s to low 80s and lows in the lower
Aviation /09z Sunday through Thursday/...
widely scattered showers and a few thunderstorms will continue
through the wee hours of the morning...with the most concentrated
activity through 09z across the Saint Lawrence valley northeast of
kart and also across the interior southern tier and western Finger
Lakes...generally south of kroc and east of kjhw. By late tonight
and early Sunday a more solid area of light rain across the upper
Ohio Valley will overspread at least the southeast half of the area.
A few embedded thunderstorms may also develop within this area of
showers from middle to late morning on. During the afternoon the more
organized showers will move a little farther south and east...and
just clip areas near the PA state line into the southern Finger
Visibility will be VFR much of the time...although some of the heavier
showers will produce brief periods of MVFR/IFR conditions. Ceilings will
also be mainly VFR through at least 10z...then a better chance of
lower ceilings will develop Sunday morning across the higher terrain as
the low levels saturate. Expect at least areas of MVFR...with some
IFR ceilings possible across the higher elevations of the southern tier
and Finger Lakes. If this materializes it may last into early
afternoon Sunday before improving. South-southwest downslope flow should keep
ceilings mainly VFR on the lake plains including most of the terminals.
Mainly VFR should prevail from late afternoon into the
evening...then lower ceilings may redevelop Sunday night across the
higher terrain in the form of low stratus.
Monday...VFR/MVFR in scattered showers and thunderstorms.
Tuesday...showers and thunderstorms likely.
Wednesday and Thursday...VFR.
moderate southerlies will continue to produce marginal Small Craft
Advisory conditions at the northeast end of Lake Ontario from Galloo
Island to Cape Vincent through early to middle morning before
diminishing. Low pressure will move across southern Quebec today
with winds becoming more southwest on the lower lakes. This will
allow winds to increase somewhat on Lake Erie...with marginal Small
Craft Advisory conditions from middle to late morning through middle to
The pressure gradient relaxes across the lower lakes tonight as low
pressure dissipates over southeast Quebec. This will allow winds and
waves to subside.
Marine...Small Craft Advisory until 6 PM EDT this evening for lez040-
Small Craft Advisory until 8 am EDT this morning for