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Area forecast discussion 
National Weather Service Buffalo New York
1045 am EDT sun Aug 2 2015

high pressure centered to our south will guarantee a nice Summer
day across our region today...with temperatures climbing well into
the 80s. A strong cold front will bring an end to our fair weather
later tonight and Monday...with strong to severe storms possible
east of the Genesee Valley Monday afternoon. A comfortably cool
airmass will follow the front Monday night and should be in place
for at least the remainder of the week.


Near term /through tonight/...
have updated the forecast to accentuate the gusty southwest winds on
the lakeshores and Niagara River...with small craft advisories in
effect this afternoon through tonight and Monday afternoon.

High pressure nosing north from the upper Ohio Valley will
produce a fine Summer day across our region today. It will be
notably warmer than the clockwise circulation around
the fair weather system will pump 850 mb temperatures to between 16 and 18c.
This will easily support afternoon highs in the middle 80s across the
lake plains and southern tier valleys...with some spots in the Genesee
Valley and Finger Lakes possibly reaching the upper 80s. The
warmth will be accompanied by a steady breeze and relatively low
dew points though (mid-up 50s) conditions should be nice for
outdoor activities.

Our weather will then deteriorate tonight as a strong cold front
from the upper Great Lakes will take aim on our region. The
front... over Lake Superior this morning...will settle across the
upper Great Lakes this afternoon and evening before pushing its
way across southern Ontario during the pre dawn hours. While some
showers and thunderstorms ahead of the front could arrive late
tonight for areas close to lakes Erie and Ontario...the bulk of
the precipitation should hold off until daybreak. Otherwise it will be a
breezy and warm night... with a strengthening southerly flow
preventing temperatures in most areas from falling below the upper
60s. Winds across the higher elevations of the southern tier and close
to Lake Erie could gust to 35 miles per hour.


Short term /Monday through Wednesday/...
on Monday upper level troughing will continue to dig
southeastward across the Great Lakes region. Meanwhile at the attendant modest surface reflection will bodily lift
northeastward over Quebec province...while slowly pushing its
trailing cold front southeastward across our area. Over the past
24 hours...the operational guidance suite has universally slowed
down the timing of the frontal passage... with most of the
guidance packages now suggesting that the boundary will pass
through our region between middle Monday afternoon and early Monday
evening...with the NAM a somewhat slower outlier compared to the
global model consensus.

While the guidance has thus come into better agreement on a later
timing of the cold front...some noteworthy disagreement remains on
the extent/evolution of convection along and ahead of this
boundary during the course of Monday. More specifically...the
European model (ecmwf)/Gem both more or less seem to suggest that a prefrontal
swath of convection will work into the area Monday morning and
then develop further/ become better organized as it presses
southeastward during the afternoon as the cold front crosses our
region during peak diurnal heating. In contrast...the GFS and
especially the NAM hint at any initial morning convection being
much more scattered in coverage and potentially even splitting our
area to the north and south...resulting in a generally dry morning
followed by additional convection developing to the Lee of the
lakes Monday afternoon as the cold front begins pushing into the
area...a scenario that is also suggested by the hiresw nmm/arw.

Given that a fairly brisk southwesterly flow will already be in
place across our region Monday morning...suspect that the latter
bunch of guidance may indeed be on to such a
scenario tends to be fairly commonplace for our area with
afternoon cold frontal passages during the Summer months. Can
easily foresee a scenario where only very limited/disorganized
convection enters our area Monday morning and potentially falls
apart as it encounters the increasingly stabilizing influences of
the lakes...with a second round of more numerous and better
organized showers/storms then initiating on lake breeze boundaries
and sweeping eastward across the area Monday afternoon.

This presents a bit of a forecast quandary as to how to handle
the pop forecast on our previous continuity pretty
much brought a solid swath of categorical probability of precipitation into the area
during the morning...then worked this southeastward across the
rest of the area Monday afternoon. Given both this and the
increasing amount of uncertainty with respect to the extent/
organization of any morning an initial step have
elected to cut probability of precipitation back to the lower end of the likely range for
Monday...while still maintaining the general idea of a region of
showers and storms pressing/developing southeastward across the
area over time. While this is not completely in line with the
thinking outlined above...this does represent a reasonable first
step in trending the forecast in that direction...and at the same
time leaves enough wiggle room for subsequent shifts to adjust
things further /in either direction/ as ultimately required.

With respect to severe potential on Monday...the operational
guidance suite suggests that modest to moderate levels of
instability (sbcapes of 500-1500 j/kg...with locally higher
pockets of up to 2000 j/kg) will develop out ahead of the
approaching cold front Monday afternoon. If such instability is
realized...plenty enough deep-layer shear (0-6 km bulk shear
values of 35-50 knots) still looks to be present to warrant at
least a chance for some stronger to severe storms...with the
primarily unidirectional flow regime dictating that damaging winds
would be the primary severe weather threat. The latest Storm Prediction Center day 2
outlook is in agreement with this thinking...and suggests a
marginal risk for severe storms from the Genesee Valley eastward
and a slight risk from our southeastern periphery eastward.

Otherwise...expect one more day of seasonable to slightly above
normal temperatures on Monday...with 850 mb temperatures in the middle teens
supporting highs mostly in the upper 70s to middle 80s...and expected
cloud cover/ convection/lake influences holding these readings
down a bit from what they otherwise would be on a fair weather

Monday night...any lingering convection associated with the front
should depart our area to the southeast during the evening as this
boundary clears our region...with a swath of relatively drier air
and subsidence in its wake leading to a return to dry and quiet
conditions for the balance of the night. With slow but steady cool
air advection also in place...overnight lows will drop back some
from the readings of the previous night...with most locations
seeing overnight lows in the upper 50s to middle 60s.

During the remainder of the period...the axis of the
aforementioned upper level trough will then continue to press
eastward across the lower Great Lakes and into New England. In
association with this...a secondary cold front will swing across
the region on Tuesday and bring another round of scattered showers
and thunderstorms...with lingering synoptic-scale showers /and
some lake enhanced showers downwind of Lake Ontario/ then
diminishing from west to east Tuesday night and Wednesday as
surface-based ridging and drier air settles across our region.
With our region firmly within the grip of the upper level
trough...a general westerly flow of progressively cooler air will
also continue across our region...with this especially the case in
the wake of the secondary cold front Tuesday night and Wednesday.
This will result in temperatures trending to solidly below normal
/but also very comfortable/ levels by midweek...with daytime highs
falling mainly into the lower 70s by Wednesday...and nighttime
lows settling into the 50s areawide.


Long term /Wednesday night through Saturday/...
the extended portion of the forecast still looks to feature broad
but persistent upper level troughing across eastern North
America...while surface-based ridging initially over our region
Wednesday night and Thursday gradually gives way to a wave of low
pressure passing across the Ohio Valley and Middle Atlantic States by
next weekend.

For our region...this pattern will result in continued below
normal but also pleasant temperatures with daily highs in the
lower to middle 70s and nighttime lows ranging through the
50s...while generally dry weather Wednesday night and Thursday
eventually gives way to renewed chances for some showers and
thunderstorms by next weekend.


Aviation /15z Sunday through Thursday/...
high pressure nosing northeast from the upper Ohio Valley will
keep fair VFR conditions in place through at least this evening.

A strong cold front over the upper Great Lakes will then approach
our region during the overnight hours. While VFR conditions will
remain in place for much of the night...showers and thunderstorms
ahead of the front could impact the region after midnight.

Along with the threat for late night thunderstorms...a 40 to 50
knot low level jet ahead of the front could produce conditions
favorable for some low level wind shear. The highest chance for
this will come over The Finger lakes region where the stronger
winds aloft will have a lower chance of mixing to the surface.

Sunday night...mainly VFR. Scattered showers and thunderstorms and
associated brief/local MVFR/IFR conditions after 06z.
Monday...VFR to occasionally MVFR with showers and storms likely.
Tuesday...mainly VFR with a chance of a few showers.
Wednesday and Thursday...mainly VFR.


southwest winds sustained 10 to 15 knots with gusts to 20 knots will
increase enough to 15 to 20 knot gusting 25 knots this afternoon...
sufficient for small craft advisories on Lake Erie...Niagara River
and Western Lake Ontario.

Conditions will further deteriorate tonight as a strong cold front
will take aim on our region from the upper Great Lakes. Winds will
freshen to near 30 knots on Lake Erie and parts of Western Lake Ontario
later tonight...with the risk for thunderstorms increasing as well.
Waves on Lake Erie will likely exceed 6 feet at times by
daybreak...with problematic waves possible by 06z. A high end Small
Craft Advisory will certainly be needed for this scenario... but
will allow recreational boaters the opportunity to enjoy todays fine
weather before issuing a Small Craft Advisory later today.

The cold front will make its way across the lower Great Lakes
Monday morning...with strong thunderstorms possible. The highest
risk for these storms will be found over the eastern half of Lake
Ontario. Along with the threat of's will likely
be in place across the lower Great Lakes for the bulk of the day.
Winds will temporarily subside across the region late Monday and
Monday night.


Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory from 2 PM this afternoon to 8 PM EDT
Monday for lez020.
Small Craft Advisory from 2 PM this afternoon to midnight
EDT Monday night for lez040-041.
Small Craft Advisory from 2 PM this afternoon to 8 PM
EDT Monday for loz030.
Small Craft Advisory from 8 PM this evening to midnight
EDT Monday night for loz043>045.
Small Craft Advisory from 2 PM this afternoon to midnight
EDT Monday night for loz042.



near term...rsh/wch
short term...jjr
long term...jjr

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