Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 220222

Area Forecast Discussion
National Weather Service Buffalo NY
1022 PM EDT Fri Jul 21 2017

High pressure will remain over the area overnight. 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 overnight,
with generally dry weather. High clouds will continue to 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

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.


Things will be quieting down considerably Tuesday, as upper level
ridging moves across the lower Great Lakes and a broad surface high
moves overhead the forecast area. The quiet weather will persist
through Tuesday night and at least the first half of Wednesday
before the high moves off the New England coast. At that point,
models are in good agreement on a potential round of showers and
thunderstorms crossing the forecast area from west to east Wednesday
afternoon and Wednesday night, as a prominent shortwave trough
crosses the region. A fairly strong upper level jet will propel the
system off to the east by Thursday morning, while a surface cool
front drops south out of Canada. With the back edge of the upper
level trough lingering across the region Thursday afternoon, we may
see a few afternoon showers pop up.

Looking at temperatures, the period will start off on the cool side,
as relatively cool air on the back side of a departing upper level
trough will still be lingering across the region. Tuesday`s highs
will be in the low to mid 70s, and a very comfortable mid 70-s at
that, with surface dewpoints in the mid 50s. The combination of high
pressure and mid 50s dewpoints will make for a cool night, with lows
in the low to mid 50s. Temperatures will warm back into the upper
70s to and potentially the lower 80s on Wednesday, with a noticeable
increase in humidity, as warm and moist air advects into the region
on southerly flow ahead of Wednesday evening`s system. Cold
advection behind this system will be negligible, though it may feel
just a little drier on Thursday.


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 overnight. 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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