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Area forecast discussion 
National Weather Service Buffalo New York
349 PM EDT Sat Jul 26 2014

Synopsis...
low pressure moving across southern Ontario will bring some showers
and a few thunderstorms through tonight. Then following a brief
break in the action Sunday morning...a more significant low will
bring a round of heavier showers and thunderstorms late Sunday
afternoon through Monday. Another push of cooler air will
arrive for the first half of next week.

&&

Near term /through Sunday/...
late this afternoon there is a weak area of low pressure centered
across the upper lakes with this low roughly aligned with a subtle
shortwave aloft. Infrared satellite and radar show scattered showers
extending southeast from this low...reaching into southern Ontario
and Central Lake Erie.

The forecast during this period will hinge on subtle convective
waves which are difficult to forecast...especially further out in
time. This said...most high resolution model guidance picks up on
the low and shortwave upstream...with quantitative precipitation forecast forecasts appearing
reasonable but perhaps a bit too slow. Our forecast will follow the
faster of this guidance (nam/hrrr) which is more in line with
upstream trends at this time. This would bring scattered showers and
possibly an isolated thunderstorm into far western New York late
this afternoon.

Showers north of Lake Ontario should get better organized with
time...taking advantage of daytime instability and better upper
level support. This should weaken overnight but still last long
enough to bring a round of showers and possibly a thunderstorm to
the north country and Eastern Lake Ontario region overnight. Expect
convection to be more spotty south of Lake Ontario...but to expand
in coverage this evening as a secondary wave of showers develops
with a pre-frontal surface trough. Expect all of this to exit to the
east late tonight with the passage of the shortwave. This should
promote some drying in the middle-levels and keep the western
two-thirds of the County Warning Area dry late tonight and into Sunday morning. Some
patchy fog is possible...mainly in the southern tier valleys with
the extent dependent on much clearing there is behind the showers.

It looks like the majority of Sunday will turn out to be dry. Model
consensus forecasts a subtle shortwave to be exiting east Monday
morning...with subtle ridging in the middle and upper levels likely to
dry things out. Later in the day..more significant rains
approach...associated with a surface low and sharp upper level
trough. However...the vast majority of 12z model guidance suggests
that this should not reach western New York until very late in the
afternoon. Storm Prediction Center does have a slight risk for severe weather on
Sunday...but this too is likely to hold off until the evening hours.
Temperatures will be similar to today...with highs in the upper 70s
to lower 80s with the cooler temperatures along the lakeshores and
across higher terrain.

&&

Short term /Sunday night through Tuesday night/...
on Sunday a weak area of elongated low pressure will settle
across New York state. With a lack of middle and upper level forcing
would expect no more than a few showers or storms...mainly in the
afternoon. As for severe weather potential...Storm Prediction Center currently has
western and central New York in a slight risk area with a lesser
risk across north-central New York. There looks to be plenty of
instability in place...however 0-6km bulk shear values only in the
25-30kt range will be a real limiting factor for severe weather to
develop. Best chance for any severe weather will remain down toward
the PA state line. Couple this with the fact that most of the day
appears that it will be dry as well. As always this situation will
monitored closely to see if anything changes. Sunday will be the
last Summer-like day for a while temperature wise with highs
generally ranging from the middle 70s to lower 80s.

Sunday night and Monday will be marked by potentially heavy rains
falling across some portion of western and central New York and the
transition to a much cooler pattern setting up across the northeast.
Thunderstorm potential will lessen as the night GOES on as more
stable air begins to move into the region. The elongated area of low
pressure will consolidate into one main low pressure system
somewhere in the vicinity of southern New York/northern PA. At the same
time a potent shortwave will be diving into the base of the upper
level trough providing plenty of lift in the middle and upper levels. A
deformation zone will also set up just to the northwest of the main
area of low pressure. This will be where the heaviest rains will
fall...which now looks to be somewhere across the southern half of
New York state/northern PA. Flooding potential will also have to be
monitored closely as well during this time period across this
region. Temperature wise there will be one more warm night with lows
generally in the low to middle 60s. Monday cooler air will begin to
build in across the area in earnest behind a cold front that will be
pushing south and east of the area. Temperatures will not recover
much on Monday with highs in the upper 60s to around 70.

After a chance of showers early Monday night things look to dry out
as surface high pressure starts to build into the area. The big
change here will be in the temperature department. The change in air
mass will be realized when you wake up Tuesday morning to lows
ranging from the upper 40s across the higher terrain...to the middle
50s near the Lake Shores.

&&

Long term /Wednesday through Saturday/...
for the remainder of the week an anomalously -3 Standard deviation
upper level long wave trough will be found over the eastern
US...with a broad ridge of high pressure over the western US. This
will allow for cool autumn like feel to the air temperatures
through the week...with the coolest day likely Tuesday where most
areas will remain in the 60s for highs. The cool 850 hpa
temperatures of around 7 to 8c on Tuesday may allow for some lake
effect rain...as well as chances for water spouts on the lakes.

Some warming middle to end of the week...though highs will only
moderate back into the low to middle 70s...still some 5 degrees or more
below normal for this time of year.

Some instability showers will be possible middle week...especially on
Wednesday when another area of deeper moisture drops southeastward
across the Great Lakes region. As an area of high pressure and drier
air builds across the Great Lakes region Thursday and
Friday...chances for showers will diminish and sunshine will
increase.

&&

Aviation /20z Saturday through Thursday/...
expect mainly VFR conditions through this evening. Scattered showers
and possibly a thunderstorm will gradually move from west-east across the
region...but these should generally result in only VFR conditions
outside of brief periods of heavier rainfall. After this...expect
drying in the middle-levels while low level moisture lingers. This may
result in a period of lower ceilings/visibility late tonight. Expect the worst
conditions at jhw...with IFR conditions likely...while elsewhere is
likely to remain in the MVFR category. Low moisture should mix out
Sunday morning...with a return to VFR conditions by late morning.
Showers and thunderstorms will develop late afternoon...but largely
should hold off until after 21z.

Outlook...
Sunday night and Monday...widespread MVFR/IFR in showers and
scattered thunderstorms. Improvement by late afternoon and
evening.
Tuesday through Thursday...mainly VFR with a chance of showers.

&&

Marine...
southwest winds will occasionally increase to around 15 knots
this afternoon and again Sunday afternoon. This will produce some
choppy wave action on the eastern portion of both lakes...but
conditions are expected to remain below Small Craft Advisory
criteria.

Another area of low pressure will move along the New York/PA border late
Sunday night and Monday. Northerly winds in the wake of this low may
bring near Small Craft Advisory conditions to the South Shore of
Lake Ontario on Monday.

&&

Buf watches/warnings/advisories...
New York...none.
Marine...none.

&&

$$

Synopsis...apffel
near term...apffel
short term...wch
long term...Thomas/wch
aviation...apffel
marine...apffel

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