Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 302030

Area Forecast Discussion
National Weather Service Buffalo NY
430 PM EDT SAT JUL 30 2016

An upper level disturbance and warm front will move into the area
late tonight and Sunday, bringing widespread showers and some
thunderstorms to most areas. Scattered showers will linger into
Monday, then dry and increasingly hot weather will return Tuesday
through Thursday.


Radar shows steady showers have exited to the east of the cwa,
following the eastward progression of a mid level wave and
departing jet streak. Some model guidance was a bit slow with
this, with the remainder of the afternoon likely to be dry in most
areas. The exception is across the Western Southern Tier where a
few showers or thunderstorms may develop, but because of lingering
cloud cover from the first round of rain any showers should be
rather sparse in areal coverage. Otherwise, the departing wave
should allow for skies to clear out with temperatures rising into
the upper 70s to lower 80s through late afternoon.

A broad upper level trough axis still across the upper lakes will
very slowly move east towards our region tonight. Model consensus
generally keeps this evening dry outside of lingering diurnal
showers across the Southern Tier. After this, an elongated 850 mb
low is forecast to lift northward into the region, which will set
up a southeasterly mid-level flow with the potential to advect
the remnants of upstream convection and also tap into Atlantic
moisture. Model guidance differs on the strength of this flow,
with the NAM generally the strongest, while much of the higher
resolution guidance NMM/ARW/HRRR is weaker and a bit slower to
generate QPF. Taking a consensus of this, expect showers
precipitation across Eastern Pennsylvania to spread out as it
moves into Central and eventually Western New York tonight. The
weak to modest low-level jet should provide a broad focus
supporting categorical POPS south and east of a Rochester to
Watertown line. There also should be some elevated instability
with a few embedded thunderstorms possible. There may be some
moderate to heavy rainfall with this, but the potential for
flooding seems small for tonight unless the low-level jet turns
out to stronger than model consensus indicates. Assuming this does
not happen, steady and occasional heavy rainfall could actually be
beneficial to the drought conditions for overnight at least.

The upper trough will continue to move very gradually east on
Sunday. By Sunday morning, confidence increases that there will be
at least some steady showers with embedded thunderstorms focusing
on much of the cwa. The exception is the Western Southern Tier,
where winds aloft will be weaker and there is a chance for a
partial clearing. If this happens, diurnally driven showers and
thunderstorms will develop in advance of the trough. Because of
the weak flow aloft, these would pose perhaps a greater potential
to cause flash flooding if they do develop. Some high resolution
guidance shows locally high QPF in the Western Southern Tier,
even though storm coverage may be less than other areas. It is
also worth noting that research has linked the approach of a
closed 500mb low to the potential for flash flooding, so keeping
this in mind have added a mention of heavy rainfall to the Western
Southern Tier.

Temperatures should fall into the lower to mid 60s tonight, with
patchy fog or stratus across the Western Southern Tier. Then for
Sunday, clouds and showers should keep highs in the 70s.


Shower and thunderstorm coverage will diminish from west to east
Sunday night through Monday as the supporting mid-level trough, low-
level moisture axis and surface low pressure shift east of New York
into New England. Precipitation should mainly be in the form of rain
showers Sunday night with diurnal instability driving isolated to
scattered thunderstorms on Monday. The highest probabilities for
rainfall are expected east of Lake Ontario Sunday night as wrap
around moisture and upslope flow should provide better forcing.
By Monday night, only a low chance of showers will be found east of
Lake Ontario with upper level ridging and surface high pressure
bringing clearing skies and dry weather by Tuesday and Tuesday night.

In terms of temperatures, cooler air aloft associated with the mid-
level trough will keep temperatures near to a touch below normal.
Highs will range from the mid 70s Monday to low 80s by Tuesday. Lows
will range from low 60s near the lakes to upper 50s across the
higher terrain each night. Humidity level should run more
comfortable compared to recent days thanks to a drier northerly flow.


Two upper level lows appear on Water Vapor Imagery this afternoon,
the first over northern British Columbia, with a second over the
Gulf of Alaska. These two features will track eastward with time,
bringing the next threat of rain showers to our region.

In the mean time a broad upper level ridge will maintain its grip
over much of the United States with building warmth over our region.
Temperatures will climb at 850 hPa into the mid to upper teens
Celsius over our region Wednesday through Friday, which will bring
mid 80s to lower 90s to the Eastern Great Lakes.

By Friday the western most shortwave will under cut the first,
eastern shortwave over central Canada. It will actually be energy
associated with the shortwave presently over British Columbia that
will eventually drop southward, behind the Gulf of Alaska shortwave,
with a mid level trough then crossing the Great Lakes region Friday
and Saturday.

Both the 12Z ECMWF and 12Z GFS are coming into good agreement with
the upper level trough pushing a cold front across the CWA between
00Z Saturday and 12Z Saturday. On Friday ahead of the cold front a
gusty southwest lake breeze off Lake Erie will likely maintain the
metro Buffalo area dry, while providing a boundary for a few
afternoon showers and thunderstorms. Thunderstorms will become
likely Friday evening and overnight ahead of the cold front, as
enhanced lift from the nearing shortwave into a very moist (PWATS
nearing 2 inches) and unstable environment occurs. Given the
instability parameters, and evening timing of convection, there is a
chance that some of these storms could become strong.

Will maintain the very warm temperatures through the day Friday,
though a little cooler over metro Buffalo and northern Jefferson
County where the lake breeze will be established. Following the cold
front passage Saturday will be a bit cooler with highs in the low to
mid 80s. With the upper level low nearby, and cyclonic flow aloft
over northern NYS, will have a chance for showers, and an isolated
thunderstorm Saturday over the Finger Lakes region, and eastern
lake ontario region.


Expect mainly dry weather through this evening with VFR conditions.
the only exception is across the Western Southern Tier where a
shower or possibly a thunderstorm cannot be ruled out at JHW.

After this, expect steadier rain to spread from east to west late
tonight and into Sunday. This will increase low moisture, with
low stratus or fog possible at JHW. Elsewhere should remain mostly
VFR however steadier rain may result in periods of MVFR conditions after
09Z tonight. There also may be some embedded thunderstorms.

By Sunday afternoon, expect mainly scattered showers and
thunderstorms, with periods of MVFR/IFR conditions in these but
otherwise VFR conditions.


Sunday night...IFR/MVFR with increasing low moisture and stratus
and fog possible.
Monday...Areas of MVFR with showers likely east of Lake Ontario,
mainly VFR with widely scattered showers elsewhere.
Tuesday through Thursday...VFR.


Persistent northeast flow will last through the weekend and produce
choppy conditions just shy of Small Craft Advisory levels along the
south shore of Lake Ontario today and tonight. On Sunday low
pressure will move slowly east across PA, while high pressure will
build across Quebec. The pressure gradient between the two may allow
for northeast winds to increase further, with a potential for Small
Craft Advisory conditions along the south shore of Lake Ontario.
Winds will diminish later Sunday night as the gradient weakens.
Winds and waves will be lower through the weekend on Lake Erie.





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