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Area forecast discussion 
National Weather Service Buffalo New York
346 PM EDT sun Apr 19 2015

a complex storm system evolving over the Midwest will push a warm
front northwards across our region tonight and early Monday...and
this will result in another soaking rain along with some gusty
winds. After a six hour break in the unsettled weather Monday
afternoon...a cold front will usher more showers and possible
thunderstorms through the area Monday night.


Near term /through Monday/...
a large expanse of quiet weather currently stretching across the
northeast Continental the forcing associated approaching middle level
wave and strong warm front still well off to our west and south.
The arrival of deep layer south/southeast flow will advect a slug
of moisture northward in the region early tonight. Primary
corridor of isentropic ascent will lift from south to north across
the region from 03z to 15z Monday beneath increasing divergent
flow aloft. Low level jet forcing will be considerable during a
good portion of this time frame as a 60-80 knot low level jet
impinges on the eastern Great Lakes. Strong moisture transport
centered within a deep 10k feet warm cloud layer will lend itself
to highly efficient hydrometeor production and several hours of
moderate rain with embedded heavier showers. Guidance consensus
indicates a general rainfall maximum of a half to three quarters
of an inch. This rainfall will likely have little impact other to
cause some minor to moderate rises on the small area tributaries
and some ponding on area roads.

The primary concern for tonight will be the strong winds that will
be produced across the higher terrain of the southern tier...and
especially the downslope winds along the lake plain of Chautauqua
and southern Erie counties. Local research has shown that a strong
southeasterly low level jet combined with a fairly strong low level
inversion near the top of the Chautauqua ridge and a fairly stable
layer to the surface will often produce very strong surface winds
along the New York thruway across Chautauqua County and southern
Erie County. The most dramatic downslope winds have been observed
during rainfree it remains uncertain if tonights
rains will play a role in dampening this risk. What is known is
that exceptionally strong 850 mb winds with a climatological
return interval of once in more than a 30 year period will be in
place...and this will most certainly produce strong wind gusts in
excess of 35 knots...with gusts in excess of 40 knots more than
possible. Will maintain the Wind Advisory currently in place for
the southern tier to cover the strong winds that should be found
along Lake Erie and also across the higher terrain. This wind
threat should diminish toward daybreak. A strong wind threat may
also develop east of Lake Ontario down the Black River valley.
Model soundings are not quite as impressive here as they are
farther to the the low level jet is not quite as
strong...but this area bears watching nonetheless.

The southeasterly flow will also help to hold temperatures up
tonight. Overnight lows should range from the upper 40s to near
50 over the far western counties to the lower 40s east of Lake
Ontario. These values will be some 10 degrees above normal.

Rain will diminish in coverage from west to east during Monday
as the Wing of strong isentropic ascent and a sizeable percentage
of middle level moisture pushes off to the northeast and area emerges
into the warm sector in wake of the warm frontal passage.
However...increasingly cyclonic flow will be spreading into
western New York during the afternoon and the abundance of remnant
low level moisture will be accompanied by steepening lapse rates
as the thermal ridge pushes northward. As a result...expect that
there will be an additional threat of scattered showers and
possible thunderstorms developing during the afternoon ahead of
approaching middle level trough axis and associated surface cold


Short term /Monday night through Tuesday night/...
Monday night a cold front will work its way across the region with
showers and scattered thunderstorms along it. Instability will
remain marginal...with daytime insolation lingering several hundred
j/kg of cape across the region. This instability in addition to
uplift along the cold front may be enough to trigger a few
thunderstorms Monday evening and will include this chance in the
forecast. Winds will remain gusty Monday evening...near 35 miles per hour east
of Lake Ontario early on a southeast flow...and then later picking
up to 35 to 40 miles per hour east of Lake Erie behind the cold front.

Tuesday and Wednesday...a broad upper level closed low will slowly
spiral eastward across southern Ontario Canada...with its center
remaining just to the north of the Great Lakes. As pockets of
vorticity stream around this upper level low...they will trigger
scattered showers...with activity likely to peak in coverage during
the afternoon hours. Will continue with chance probability of precipitation through the
remainder of the time period...with likely all areas to receive at
least some rainfall over this 2-day stretch.

Though the upper level low...and the core of the cold air remains
just to our north...middle level lapse rates will increase to 8-9 c/km.
These lapse rates in additional to daytime insolation may trigger a
few rumbles of thunder...across western New York on Tuesday and east
of Lake Ontario on Wednesday. Confidence remains too low at this
point in time to include thunderstorms in the forecast.

Following the passage of the cold front...the recent nice stretch of
warmth will be erased with highs Tuesday and Wednesday in the
40s...and nighttime lows dropping back into the 30s. These daytime
readings will average 10 degrees or so below normal.


Long term /Wednesday through Sunday/...
an upper level low will slowly spiral across the Great Lakes and
towards the northeast this time period. Under this low pressure
expect cloudy days with scattered rain showers for Thursday and
Friday. Though the upper level low will advance eastward for next
weekend...there will be vorticity maxes rotating around the feature such
that a chance for rain showers will continue to be possible...
especially across eastern zones which will lie closer to the
upper level low. Shower chances will again be greatest in the
afternoon hours with daytime heating...with fewer showers to be
found by night. There may even be some wet snow mixing in at night
across the region. Daytime air temperatures will average 5 to 10
degrees below normal to start this period. Then as the upper level
low slowly pushes eastward some moderation in the air temperatures
are expected from west to east.


Aviation /20z Sunday through Friday/...
high pressure over eastern Canada will keep fair VFR conditions in
place across all of western and north central New York through the

Conditions will deteriorate tonight though as a complex storm system
over the middle west will advance to the upper Great Lakes. An
associated warm front will push north across the western counties in
the process...with lowering ceilings and widespread rain leading to MVFR
conditions. IFR conditions will be possible across the higher
terrain of the southern tier.

The greatest concern tonight though will come from a very strong low
level jet that will produce gusty winds across the higher terrain of
the southern tier and also along the lake plain of Chautauqua and
southern Erie counties. Surface winds at kjhw and kjhw may gust to 40
knots while winds at 3k feet will range from 60-80 kts. While the core
of the highly anomalous low level jet may be too high to produce
true low level wind shear is certainly Worth
mentioning in this discussion.

Monday...areas of MVFR with occasional showers and strong gusty
Tuesday through Friday...VFR/MVFR with scattered showers.


high pressure over eastern Canada will drift east and give way to a
deepening...complex storm system over the Midwest. This will lead
to a tightening of the surface pressure gradient over the lower
Great Lakes tonight...with freshening offshore winds of 20 to 30
knots supporting small craft advisories for all of the New York
nearshore waters through Monday.


Buf watches/warnings/advisories...
New York...Wind Advisory from 8 PM this evening to 8 am EDT Monday for
Marine...Small Craft Advisory from 8 PM this evening to noon EDT Monday
for lez040-041.
Small Craft Advisory from 11 PM this evening to 11 am EDT
Monday for lez020.
Small Craft Advisory until 8 PM EDT Monday for loz042-
Small Craft Advisory from 8 PM this evening to 11 PM EDT
Monday for loz044-045.



near term...tma
short term...Thomas
long term...Thomas

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