Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 211826

Area Forecast Discussion
National Weather Service Buffalo NY
226 PM EDT Fri Jul 21 2017

High pressure will remain over the area through tonight. A
frontal boundary will then set up in the vicinity of the lower
Great Lakes this weekend, bringing periods of unsettled weather
and near normal temperatures through Monday. Then high pressure
will build across the region during the middle of next week which
will provide several days of pleasant weather.


Weak surface high pressure will influence our weather through
tonight, with generally dry weather. There is a slight chance of
a shower with a shortwave across the Saint Lawrence Valley late
this afternoon. Otherwise, model consensus keeps the region dry
through daybreak Saturday morning.

Expect partly to mostly sunny skies for the remainder of this
afternoon. After this, high clouds will gradually spread into
the region from the west, with this cloud cover thickening late
in the night. Despite light winds, this will limit radiational
cooling somewhat tonight, especially late. Even so, expect
temperatures to drop off quickly this evening, with some patchy
valley fog possible in the Southern Tier. Temperatures late this
afternoon will generally range from around 80 to the mid 80s.
Lows tonight will be in the upper 50s to mid 60s with the
coolest readings across the interior valleys of the Southern
Tier and North Country.

For Saturday, model guidance has come into better agreement with
most guidance tracking a convective complex across or south of the
Western Southern Tier. Mainly light showers may clip areas
north of this, but chances of any rain diminish to the north. It
is important to note that our area, if anything, will be on the
northern fringe of that system which has a minimal risk for
severe weather. Following this, SPC has shifted the slight risk
area to the NY/PA state line. Given uncertainty in the track,
there is still a marginal risk for gusty winds and heavy rain
across the Southern Tier, but this risk appears diminished based
on latest guidance. Otherwise, expect near normal temperatures
with highs in the upper 70s to lower 80s.


The bulk of the unsettled weather during this period looks to occur
later Sunday into Monday where 12z model guidance consensus shows at
least one area of low pressure with a slow moving frontal boundary
crossing our region as a sharp mid-level trough shifts over the
eastern Great Lakes. This will all come together to produce a few
periods of showers and thunderstorms to close out the weekend and
start the new work week. Have cut back POPs on Saturday night as it
appears that high pressure centered near James Bay will be ridged
south across Lake Ontario which should shield much of western NY
from shower and thunderstorm activity overnight. Have left a
low/slight chance in play as a surface low shifting just to our
southwest along the slow moving boundary may force a few showers
north across the NY border.

Large scale lift and southerly flow ahead of low pressure forming
over Lake Erie/Western NY through Sunday will begin to shift a
surface warm front northeast across western and central NY. Timing
of its position still needs to be refined in mesoscale guidance but
generally ramped up chance POPs in the official forecast from
southwest to northeast across the region with likely range POPs in
place across WNY by late afternoon where newly formed low pressure
should be centered. The most likely period of shower and
thunderstorm activity seems to be centered on Sunday night and
Monday morning as the low shifts east either across Northern New
York into New England or across eastern NY then off the coast of
Cape Cod. By Monday night the consensus of the models shows the low
positioned off the New England coast with high pressure then in the
process of building back across the Great Lakes along with
developing cool northerly flow. Have tapered POPs back as the low
departs leaving dry weather across WNY Monday night with just low
chance POPs over CNY.

There is some concern for potential hazardous weather during this
period. Pwats rising to between 1.5-1.8 inches along the warm front
just ahead of the surface low may bring a risk of heavy downpours
and flooding especially if storms train along any surface
boundaries. There is also a risk for severe winds and maybe some
small hail with any storms that develop in building instability
Sunday and lingering into Sunday evening where GFS forecast Bulk
shear to 40kts. Veering vertical wind profiles in forecast soundings
may even bring about another isolated tornado risk. SPC has included
a Slight/Marginal risk area for Sunday-Sunday night in our forecast
area. These potential hazards will also continue to be highlighted
in the Hazardous Weather Outlook.

Temperature-wise, Highs in the upper 70s to low 80s Sunday will be
cooler on Monday only topping out in the mid 70s on the backside of
the passing low. Overnight lows will bottom out in the 60s Saturday
night and Sunday night then slip to 50s Monday night with cool
Northerly flow.


Tuesday, high pressure and cooler/drier air will be found over our
area...with fair and dry weather then following for Wednesday as the
surface high settles directly overhead. Toward the end of the
period...the high will slide off to our east and allow a weak cold
front to push into the region from the Upper Great Lakes...thereby
allowing for lower-end chances for showers to return by Thursday.

Regarding temperatures...the aforementioned arrival of cooler and drier
air will translate into temperatures and humidity levels falling off
through Tuesday...which should feature daytime highs generally in the
mid 70s and comfortable dewpoints in the mid to upper 50s. Both will then
rebound some through the rest of the period as the axis of the ridge slides
to our east and a southwesterly return flow develops on its backside...
resulting in temps climbing back to around 80 degrees and dewpoints
recovering to around 60 or so.


High pressure will remain across the region through much of the
night with mainly VFR conditions. The only exception is that
there is a chance for valley fog to develop at JHW. Fog should
be less widespread than last night with high clouds building
across the region which will slow radiational cooling and fog.

On Saturday, a showers and thunderstorms will track along a
stalled frontal boundary with the core of this likely to pass
south of BUF-ROC around mid-day. Expect mainly VFR conditions
north of this with MVFR or lower in showers and thunderstorms at

Saturday night and Sunday...VFR/MVFR with some showers and
Monday...Mainly VFR but with a chance of showers.
Tuesday and Wednesday...VFR.


High pressure over the upper Great Lakes will expand across the
lower Great Lakes through tonight. This will result in fine
conditons for recreational boating. A frontal boundary is then
expected to stall near the lower Great Lakes this weekend with
chances of showers and storms becoming a threat, but winds/waves
are expected to remain on the light side.





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