Area Forecast Discussion
Issued by NWS Buffalo, NY

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FXUS61 KBUF 210214

Area Forecast Discussion
National Weather Service Buffalo NY
1014 PM EDT WED JUL 20 2016

High pressure will drift across the region tonight bringing a
continuation of mainly clear skies. The surface high will settle off
the east coast Thursday allowing heat and humidity to build across
the region through the weekend. Scattered strong thunderstorms are
possible across the region Friday ahead of an approaching weak cold
front, and again Sunday night and Monday with another weak cold


IR satellite imagery showing clear skies across the entire region,
with high pressure providing plenty of dry air and subsidence.

Overnight, the lack of cloud cover, mostly light winds, and dry
airmass under the surface high will promote good radiational
cooling. Temperatures will drop into the upper 50s to lower 60s on
the lake plains, and around 50 in the cooler Southern Tier valleys
and Lewis County. The relatively low dew points should limit the
southern tier valley fog, but some isolated to patchy fog cannot be
ruled out there along the upper Allegheny and upper Genesee

Heat will build into the region Thursday as the surface high settles
off the Mid Atlantic coast. 850 mb temperatures will surge to about
+20C by late Thursday afternoon, with only some increasing thin high
cloud cover doing little to counter the warmer airmass. High
temperatures will ramp up into the upper 80s to lower 90s, with the
warmest readings along the Genesee Valley and northern Finger Lakes
region. Gradient southwest flow off the lakes will keep the Buffalo
and Watertown areas slightly cooler. Thursday will be relatively dry
compared to more humid days to come this weekend, as dew points in
the upper 40s in the Southern Tier to the mid to upper 50s near the
lakes will keep the heat somewhat tolerable. Dew points will finally
start to surge into the 60s by Thursday evening ahead of the next
approaching shortwave along with increasing mid and high level cloud


An anomalously strong 593dm ridge will remain across the Plains but
will influence our region with continued hot weather.

The hot afternoons through the upcoming weekend will be accompanied
by overnight lows that will be in the 70s across the more densely
populated lake plains. This means that our temperatures will average
5 to as much as 10 deg f above normal throughout the period...which
is made even more impressive knowing that we are in the midst of our
thermal solstice. It is also interesting that the above normal
temperatures and current moderate to severe drought will feed upon
each other...with the alarmingly dry antecedent soil conditions
adding several degrees to daytime highs while the higher temps will
further exacerbate the problems associated with the drought.

As we head into the upcoming weekend...a Pacific based shortwave
pushing across the Northern Rockies will basically flatten the
impressive ridge. Meanwhile...lowering hgts near Hawaii will
encourage the heart of the newly flattened ridge to retrograde back
across the Desert Southwest to the California Coast. This will leave
a seasonally biased area of high pressure that will monopolize the
weather between 20-35 N from Hawaii to the Southeast Coast...while
downstream troughing over the St Lawrence Valley will eventually
allow a legitimate cold front to push through with a refreshingly
cooler and less humid airmass. More on that in the long term

As for the day to day details...

Thursday night a cold frontal boundary will push south across
Southern Ontario. Convection that will have had previously blown up
well ahead of the front could sustain itself as it pushes south
across Lake Ontario early in the night... and if it should
encounter an unstable airmass over Western and North Central New
York. Given the northwesterly flow aloft...there will also be
favorable kinematics to induce bulk shear values in excess of 40
knots. This would be favorable for strong to severe convection with
an emphasis being placed on damaging straight line winds. The most
favorable area for such activity should be west of the Finger Lakes
where organized convection would likely build southeast into the
most unstable air. SPC has included the forecast area within a
Marginal Risk for severe storms. Temperatures Thursday night will
likely remain above 70 for the majority of the region.

On Friday...any strong storms from the previous night should have
since weakened and pushed south...while another area of convection
associated with a cold front will take aim on the region. Between
the two batches of storms...there will likely be a 3-6 hour window
of uneventful weather...but this will be nearly impossible to narrow
down from this vantage point given the timing and strength of the
original convection. In any case...the cold front will push south
across the forecast area during the midday and afternoon. As the
atmosphere heats back up and `re-loads`...the stage could be set for
another round of strong storms. Another SPC Marginal Risk for severe
storms has been highlighted across the forecast area with a Slight
Risk further east. Otherwise it will be very warm and humid with H85
temps in the upper teens supporting afternoon temperatures in the
upper 80s to near 90 for the lake plains and most valleys.

The cold front will push south of our region Friday night while
drier air will make its way across the Lower Great Lakes. Any
lingering showers or storms will end early with skies clearing from
the northwest during the course of the night. Unfortunately...there
is not expected to be a real change in temperatures
will be similar to those from the previous night.

On Saturday...high pressure will build back across our region with
dry weather while a reinforcing push of oppressive warmth will make
its way across the Lower Great Lakes. H85 temps should again be in
the upper teens to near our afternoon temps will climb back
towards 90 away from the lakes and higher terrain. Fair weather can
be anticipated into Saturday night with high pressure still over the
region. Temps Saturday night will again hold well above normal.

The western flank of the ridge will bring a return of heat and
humidity Sunday. Temps will once again rise into the mid to upper
80s. The next area of convection will be associated ahead of an
incoming cold front and strong shortwave trough. Will carry chance
pops for Sunday night, with a another warm night in the mid 60s to
lower 70s.


A cold front and sharp mid-level shortwave trough look to cross our
forecast area on Monday bringing a threat of showers and
thunderstorms and what looks like a nice break in the weekend heat
behind the front. 12z GFS and ECMWF runs show good agreement on the
timing of the front which could work with the daytime heating cycle
to cut through a decently sheared and unstable airmass potentially
triggering strong to severe storms. Have continued high end chance
POPs as its tough to go any higher at this range while in drought.
Temperatures and humidity levels on Monday will remain warm and
sticky ahead of the front with highs forecast in the mid 80s and
dewpoints in the upper 60s to around 70.

Central Canadian sourced continental polar high pressure is forecast
to edge south across the Great Lakes in the wake of the front and
bring a more comfortable airmass with temperatures closer to normal
levels by mid next week. Have included slight/low chance POPs
through Monday night-Tuesday with some uncertainty as to the speed
the front will exit our region. Dry weather expected by Wednesday
with temperatures only running a touch above normal and dewpoints in
a more comfortable range of upper 50s to low 60s.


High pressure will remain across the lower Great Lakes region
tonight with clear skies and light winds. There may be some limited
patchy valley fog across the Southern Tier with local IFR from 06Z-
12Z Thurs, but this should not impact KJHW. Otherwise VFR will
prevail for the rest of the area.

High pressure will drift off the Mid Atlantic coast on Thursday,
remaining close enough to support more subsidence and drying with
VFR prevailing. Expect just a modest increase in high cirrus level
cloudiness later in the day ahead of a weak cold front moving into
the central Great Lakes.

Friday...Mainly VFR with a chance of showers and thunderstorms and
associated brief MVFR/IFR.
Saturday and Sunday...VFR.
Sunday night and Monday... Mainly VFR with a chance of showers and
thunderstorms and associated brief MVFR/IFR.


High pressure will remain across the lower Great Lakes through
tonight, with light winds and flat wave action lasting through
Thursday. A weak front will cross the region Friday bringing some
scattered showers and thunderstorms a bit more wind and chop on the
lakes, but winds and waves will likely remain below small craft
advisory criteria. High pressure will build across the lakes again
this weekend and promote more fine boating conditions.





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