Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
323 PM EDT Friday Sep 4 2015
high pressure will become anchored along the East Coast through the
Holiday weekend and provide dry and very warm weather for the bulk
of the region. There will be a few widely scattered thunderstorms
Saturday afternoon for a small area just east of Lake Erie...and
then possibly on Sunday southeast of both lakes but the vast
majority of the area will remain dry. The above normal temperatures
will last through most of next week before cooler weather arrives
late in the week.
Near term /through Saturday/...
radar imagery late this afternoon showing a few scattered showers
and storms across the southwest corner of New York along a subtle
convergence zone supported by terrain and differential heating. Low
and middle level flow is very weak...so these storms will have slow
forward motions and may produce locally heavy rainfall in a few
spots. These storms will continue through early to middle evening
before diminishing with the loss of daytime heating. Otherwise the
rest of the area will see plenty of sunshine and warm temperatures
to wrap up the day.
Overnight the latest 12z NAM and Canadian Gem suggest a low stratus
deck will form across central PA and spread northwestward into
portions of the southern tier and Finger Lakes with increasing
clouds across the higher terrain. Elsewhere skies should remain
mainly clear as a bubble of slightly drier air has pushed south out
Patchy fog will form once again in many areas with fog becoming more
widespread in the typical southern tier river valleys. Expect lows
in the middle 60s in most areas...with upper 50s across the north
country where a slightly cooler/drier airmass has settled in.
On Saturday the morning fog and stratus across the southern tier and
Finger Lakes should mix out by late morning. The remaining low level
moisture will allow diurnal cumulus to form across the higher
terrain of the southern tier. Strong heating will combine with
abundant moisture to produce moderate to strong instability by
afternoon with model point soundings forecasting SBCAPE of greater
than 2000j/kg. For the most part the very warm middle levels and lack
of large scale support will prevent deep moist convection with one
notable exception. Latest 12z mesoscale model guidance is now more
aggressive in developing convection along the Lake Erie lake breeze
in Chautauqua and southern Erie counties. Locally stronger
convergence along the lake breeze boundary may be enough to overcome
the warm middle levels and breach the cap...allowing scattered storms
to develop. With this in mind have included a narrow corridor of
chance probability of precipitation Saturday afternoon and early evening from Findlay Lake
northeast into the Boston Hills.
Otherwise for the rest of the area expect plenty of sunshine on the
lake plains. 850mb temperatures around +16c will continue to support
unseasonable warmth with highs in the middle to upper 80s across the
lower elevations of western New York...and lower 80s across higher
terrain. Light synoptic scale flow and strong differential heating
will allow local lake breeze circulations to develop...keeping the
lakeshores a little cooler.
Short term /Saturday night through Monday night/...
a broad upper level ridge will be over the eastern half of the
country Sunday and Monday while an upper level low moves from the
Pacific northwest into Saskatchewan and Manitoba. The latter
feature will have some impacts later on in the week...but in the
meantime mainly dry and continued warm conditions will continue
under the presence of the ridge.
A weak SW flow will develop by Sunday. Lake breeze convective
initiation is possible well inland late in the day east of either
lake...but overall expect dry conditions for most of western and
central New York. By Monday...a slightly drier airmass should be in place
for dry conditions regionwide. The usual late season valley fog is
possible along with some low cloudiness for the overnights.
Long term /Tuesday through Friday/...
there is uncertainty in the models regarding a weak frontal passage
on Tuesday. A better cold front looks plausible for roughly the
Wednesday timeframe as an upper level low over Manitoba moves slowly
east across the Hudson Bay. Thursday should be mostly postfrontal
and dry. Then uncertainty creeps back into the forecast with quite
a bit of variability to timing and placement of surface features
over the eastern US by Friday.
From a probabilistic standpoint...will place the highest threat of
precipitation in for the Wednesday time period...with lower threats
Tuesday...Thu...and Friday. Confidence in gradually lowering temperatures
is high however.
Aviation /20z Friday through Wednesday/...
diurnal cumulus with bases in the 3-4k foot range will continue
across the higher terrain of the southern tier and Finger Lakes this
afternoon. A few widely scattered showers and storms will continue
through early evening across the southwest corner of the state near
kjhw. Otherwise for the rest of the area mainly clear skies and VFR
will prevail through the afternoon and evening.
Tonight the diurnal cumulus will dissipate early in the evening with
the loss of daytime heating. Latest model guidance suggests a low
stratus deck will develop overnight across central PA and spread
northeast into portions of the southern tier and Finger Lakes with
areas of MVFR/IFR ceilings developing across the higher terrain. River
Valley fog will also form across the southern tier with areas of IFR
visibility. Elsewhere some light br may develop again tonight with areas
of MVFR visibility from 06z-13z.
On Saturday most of the light morning br will burn off by 13-14z.
The fog and stratus will linger a few hours longer across the
southern tier but should mix out by late morning. Diurnal cumulus
will develop once again across the higher terrain of the southern
tier and Finger Lakes. Latest model guidance supports the
development of widely scattered convection during the afternoon along
a Lake Erie lake breeze boundary from near kjhw to just south of
kbuf. Otherwise the rest of the area will see mainly clear skies and
Sunday and Monday...VFR. Localized IFR in overnight/early am fog.
Tuesday and Wednesday...mainly VFR with a chance of showers and
moderate northeast winds will continue to produce choppy conditions
and marginal Small Craft Advisory criteria on Lake Ontario through
this evening before winds diminish overnight. High pressure will
then take up residence along the East Coast for the Holiday weekend.
This will provide light winds and flat wave action through the
entire long weekend. The flat lakes and warm temperatures will
provide excellent boating conditions...although winds will be on the
light side for sailors.
Marine...Small Craft Advisory until 11 PM EDT this evening for loz042.