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Area forecast discussion 
National Weather Service Buffalo New York
157 am EDT Tuesday Oct 13 2015

a cold front will pass through the region overnight...producing some
showers while ushering in more seasonable conditions for the
remainder of the week. By the weekend will become quite
chilly. The weather will turn more unsettled with multiple chances
for showers through the weekend... some of which will be lake


Near term /through today/...
deepening low pressure will Cross Lake Superior into central
Ontario...and push its associated cold front through our forecast
area overnight and early Tuesday. This will bring an abrupt end to
our unseasonably warm and dry weather... while also generating
some rain shower activity.

Radar shows a scattered line of showers out ahead of this boundary.
This area corresponds to the leading edge of a 40 knots 850mb low level jet.
Strengthening frontogenetic forcing and lift supplied by an exiting
100 knots h25 jet over eastern Ontario should promote more widespread
showers over The Finger lakes region and particularly the Eastern
Lake Ontario region. Model consensus and radar trends both support
likely probability of precipitation...with a narrow band of showers forecast to expand as it
moves into our area late tonight.

The amounts of rain will vary with basin average quantitative precipitation forecast into Tuesday
morning under a tenth of an inch over the far western counties...
upward to a quarter inch east of Lake Ontario. Locally higher
amounts can be expected due to the initial round of convection
out ahead of the front.

Synoptic rain will end from west to east during the morning on
Tuesday...then cooling boundary layer temperatures will start to kick off
some weak lake effect response initially near Buffalo in the morning
then settling along the Chautauqua ridge by late morning through the
afternoon. Eventually the Tug Hill plateau will become involved by
this afternoon once the cooler 850mb temperatures reach Eastern Lake

Temperatures will be on a downward track from this evening right
through the day on Tuesday as colder air follows the passage of the
cold front. Expect temperatures tonight in the 60s to middle 50s...then
middle 50s to low 60s early Tuesday falling to upper 40s and low 50s by
the end of the day.


Short term /tonight through Thursday night/...
in the wake of the passage of tuesday's strong upper level trough we
will see a secondary shortwave drop across the lower Great Lakes
Tuesday night that will help deepen the longwave trough setting up
across eastern North America. Synoptic lift associated with this
wave coupled with increasing cold air advection and resultant lake
enhancement will generate scattered rain showers across much of the
forecast area with greatest concentration of shower activity being
found across the southern tier and north country. The one factor
that will limit the intensity of the showers that develop will be
shallow nature of the moisture with the bulk of the moisture being
contained below 7kft and a substantial middle-level inversion.

Lake effect showers will linger into Wednesday with further
diminishing intensity and coverage through the day owing to diurnal
disruption of the lake effect in addition to negative vorticity advection behind the
departing shortwave. Precipitation chances will drop off further Wednesday
night as surface ridging driven by a subtle middle-level shortwave
moves across the forecast area. However...we may see another round
of showers develop across the north country later Wednesday night
into Thursday as yet another shortwave trough is prognosticated to drop
across Georgian Bay before transiting the north country. Aside from
this feature in the north country the rest of the forecast area
should experience a dry but cloudy day Thursday as flow backs to the
south and increasing warm advection effectively eliminates any
lingering lake effect. This warm advection will be developing ahead
of the next storm system that will be impacting the forecast area
Thursday night...

Regarding temperatures...the prevailing westerly flow off of the
lakes along with the abundant cloud cover that will accompany the
above-mentioned systems well help to moderate temperatures with lows
Tuesday night falling into the middle to upper 40s. Conversely...these
factors will also prevent temperatures from rising much on
Wednesday...particularly as more cold air will advect across the
lower Great Lakes in the wake of Tuesday night's shortwave. Look for
highs to only creep into the lower 50s. This colder airmass will
cause temperatures to drop into the lower 40s Wednesday night with
middle to upper 30s in the southern tier and north country...however
winds should remain breezy enough to prevent frost formation. Moving
into Thursday...temperatures will rise back into the 50s on the
heels of increasing southerly flow and warm advection.


Long term /Friday through Monday/...
unsettled weather will persist through the end of the week and at
least through the first half of the coming weekend as the longwave
trough will remain stubbornly in place across the northeastern U.S.
It currently appears that Thursday night into Friday should bring
widespread rainfall as a potent shortwave moving through the base of
the longwave trough crosses the lower Great Lakes with the only
issue being the speed with which this system transits the forecast
area as there continue to be relatively minor timing differences
between the models.

Lake effect showers will once again develop across the lower Great
Lakes Friday into Friday night...depending on how quickly the
aforementioned storm system departs the area. The big question for
the weekend continues to be the potential for snow this weekend. The
GFS continues to be the coldest of the global suites...taking 850mb
temperatures down to -7 to -8c on Saturday. It is notable that the 12z
European model (ecmwf) is also starting to trend colder...with 850mb temperatures falling to
-6c all the way to the PA border on Saturday. Given these
factors...have opted to include snow across the higher terrain
Friday and Saturday night with a rain snow mix across lower
elevations. Any accumulations may be limited by the shallow nature
of the moisture...however it must be noted that we are still very
far out to make any definitive calls on accumulations...if any.


Aviation /06z Tuesday through Saturday/...
expect VFR conditions to last much of the overnight...with southerly
winds downsloping and helping keep ceilings in the VFR category.
Steadier showers will spread from west to east and likely lower
conditions into the MVFR category at times early this morning. Areas
of IFR ceilings are also possible / although not likely/ with the best
chance for these right along the frontal boundary...and across
higher terrain such as jhw.

Colder air behind the front on Tuesday will get low-level moisture
from the lakes involved... helping ceilings to become more MVFR than VFR
through Tuesday afternoon. Continued cooling Tuesday and weakening
mixing will allow MVFR ceilings to dominated with some IFR ceilings expected
to develop over the southern tier including kjhw.


Wednesday through Saturday...VFR/MVFR with a chance of showers.


an approaching cold front over Upper Michigan to keep a relatively
tight surface pressure gradient over the lower Great Lakes.
Southerly winds will become southwesterly following the frontal
passage. Colder air and increased wind speeds will require that
Small Craft Advisory in effect for Lake Erie nearshores extend into
Wednesday evening...and the nearshore marine zones of Lake Ontario
get small craft advisories from Tuesday morning through Wednesday


Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory until midnight EDT Wednesday night for
Small Craft Advisory from 11 am this morning to 6 am
EDT Thursday for loz042-043.
Small Craft Advisory from 6 PM this evening to 6 am EDT
Thursday for loz044-045.


near term...apffel/church/wch
short term...wood
long term...wood

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