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Area forecast discussion
National Weather Service Buffalo New York
618 am EDT sun Sep 15 2019

high pressure over the upper Ohio Valley will maintain quiet and
dry weather through this morning. A couple of weak disturbances
will then bring some light showers between this afternoon and
Monday...before high pressure returns and brings a prolonged
stretch of fair dry weather and above normal temperatures for
the rest of the week.


Near term /through tonight/...
through the first part of this morning high pressure centered
over the upper Ohio Valley will maintain dry and quiet weather
across our region...with just the usual valley fog found across
the southern tier...and some much patchier fog elsewhere. All
such fog will dissipate by a few hours after sunrise.

Otherwise...flat subtropical ridging over the southern half of the
nation will begin to amplify northward across the plains states and
upper Great Lakes today and response to digging upper
level troughing along the Pacific coastline. Downstream of this building
ridge...a modestly cyclonic upper level flow will be in place from
the central Great Lakes into New England...with a couple of shortwave
disturbances sliding southeastward through the larger-scale flow and
passing across New York state and nearby southern Ontario. Over the
last 24 hours...the model guidance has continued to trend faster/
further south and more amplified with these features...which will
result in our weather becoming somewhat more unsettled again after
the dry and quiet start to today.

The first of the aforementioned disturbances is currently located
over the upper Great Lakes...where it is currently generating a
pretty decent swath of showers. This feature will dig southeastward
through the course of this morning and reach far western New York
this afternoon...before weakening some and sliding off to our
southeast by early this evening. Out ahead of this wave...a fairly
sunny start to the day will quickly give way to increasing clouds from
northwest to southeast through the midday to early afternoon hours...
with increasing lift/moisture attendant to the wave and a corresponding
35-40 knot low level jet then bringing at least some scattered showers
into the area in a similar fashion through the end of the day. The
shower chances will be maximized across far western New York...where
the deepest moisture and best combination of forcing from the shortwave
and low level jet will be realized...and where pops have consequently
been bumped up to the low likely range. Meanwhile...the lowest
potential for showers will be found across interior portions of the
southern tier and across the Saint Lawrence valley...where notably
less favorable moisture and less in the way of lift may only lead to
some isolated to widely scattered activity. Otherwise...temperatures
will range from the mid to upper 60s east and immediately south of
Lake Ontario to the lower 70s across most of western New York.

As we move into tonight...the second shortwave will move into our
region. The passage of this wave will be a bit different from the
first in that it will have the benefit of a supporting mid level trough
and will also be accompanied by the passage of a weak surface wave...
with these latter two features helping to advect a better slug of
moisture (pwats of ~1.5 to 1.75 inches) into our region while also
providing additional forcing for ascent. The end result of all this
will be a second round of scattered to numerous light showers that
will push southeastward across much of our area...with chances for
these maximized across the Niagara Frontier and Finger Lakes...which
will be situated underneath a developing/southward-sagging frontal
zone. North of this boundary...shower potential should rapidly decrease
with increasing northward extent across the north country...with the
Saint Lawrence valley and northern portions of Jefferson and Lewis
counties more than likely to be mainly if not totally dry. With respect
to low temperatures...these will range from the lower 50s across the
north country (which will lie in the cooler airmass north of the
aforementioned frontal boundary) to the upper 50s and lower 60s
across western New York.


Short term /Monday through Wednesday night/...
this period will be dominated by an anomalously strong 500 mb ridge that
will amplify while slowly drifting east across the Mississippi
Valley and upper Great Lakes. While there will be a few nuisance
showers over our region on Monday...being immediately downstream
from the high amplitude ridge will guarantee fair dry weather for
the remainder of the time frame. Meanwhile...daily temperatures will
climb a few degrees each day...averaging above normal for the
period. As for the day to day details...

A shortwave will be in the process of crossing New England Monday
morning...while trailing energy in the mid levels will support a
weak surface reflection over our forecast area. Lift from this
exiting feature will not be am only anticipating
nuisance showers (mainly in the am) over the western counties with
quantitative precipitation forecast under a tenth of an inch. The north country may stay pcpn free
and will most certainly clear much faster than the western counties.
A north to northeast upslope flow in the low levels will retard the
progression of the clouds will be common over the
western counties through at least midday. Gradual clearing will then
take place during the course of the afternoon with the southern tier
possibly remaining cloudy until around dinnertime. Temperatures will
be near...or just a skosh above normal with highs in the upper 60s
to near 70.

High pressure centered over Quebec late Monday will build south
across the lower Great Lakes Monday night. This will not only
promote the low level flow to veer more to the east (thus removing
the upslope component)...but it will also help to advect even drier
air into our region. This will lead to clear skies...and with a
light wind in place...good radiational cooling can be anticipated.
It will become quite cool with mins in the 40s away from the lakes.
This cooling will also be favorable for late night valley fog in the
vcnty of the 'warmer' tributaries.

The large surface high will become centered over the St Lawrence
Valley Tuesday and Tuesday night. This will insure beautiful weather
for Tuesday with sun filled skies helping afternoon temperatures
reach the upper 60s to lower 70s. Another starlit night will follow
with mins Tuesday night generally ranging from 45 to 50...very
similar to the previous night.

A robust shortwave ejecting out of the intermountain-west Tuesday
evening will cross the Canadian prairies before tracking east across
Ontario Wednesday and Wednesday night. This will effectively shove
the northern nose of the impressive 500 mb ridge across Quebec and open
the door for warm advection to finally become established over our
forecast area. Meanwhile...the corresponding strong surface high
will be centered roughly over New England. This will maintain
gorgeous weather over our forecast area with continued clear skies
and comfortable temperatures.


Long term /Thursday through Saturday/...
..spectacular weather for the end of astronomical Summer...

There is exceptionally high confidence that we will experience above
normal temperatures during this period...with near equal assurance
that it will be accompanied by fair dry conditions.

The basis for the brimming certainty is the persistent (several days
Worth of model runs)...strong agreement between the gefs ensembles
and the operational European model (ecmwf) that a 590dm sub tropical ridge will be
parked over the lower Mississippi Valley. The ridge will extend
to the northeast across the lower Great Lakes...while strong high
pressure will be in the vcnty of New England. This combination will
strongly favor sunny days and fair nights with temperatures that
will average some 5 to 10 degrees above normal. 850 mb temps that will
range from 10 to 12c at the start of this three day period will warm
into the mid teens by the weekend. This will easily support
afternoons highs in the 70s...with 80s expected for Friday and
moreso for Saturday. The relatively warm weather should persist
through the remainder of the weekend as well before any pattern
change takes place.


Aviation /10z Sunday through Thursday/...
through early to mid morning...unlimited VFR conditions will largely
prevail across our region thanks to high pressure centered over the
upper Ohio Valley. The main exception to this will be across the
southern tier...where the usual overnight/early morning valley
fog will produce some localized LIFR to IFR restrictions before
dissipating a few hours after sunrise. The above said...there may
also be a little patchy IFR/MVFR fog elsewhere through about 12z.

Later this morning and this afternoon the first in a pair of
disturbances will approach and cross our region. This will initially
bring increasing clouds and lowering VFR ceilings from northwest
to southeast later this morning and early this afternoon...followed
by a round of scattered light showers (more numerous across far
western new york) through the rest of the day. At this point it
appears that conditions will remain primarily VFR into this
evening...though cannot rule out some brief/localized MVFR in
tandem with the aforementioned showers.

Tonight a second disturbance will move into our region...along
with a weak area of surface low pressure. This will bring another
round of scattered to numerous showers mainly to areas south of
Lake Ontario...with chances for these maximized in the vicinity
of a developing/slowly sagging surface boundary across the Niagara
Frontier and Finger Lakes regions. The combination of further
moistening of the low levels and a developing northeasterly upslope
flow to the north of the front should also result in flight conditions
generally deteriorating into the MVFR range south of Lake Ontario...
with some areas of IFR not out of the question late across the
higher terrain and also to the immediate north of the surface
front. Meanwhile...the north country should remain primarily VFR.

Monday...scattered showers ending...with MVFR/possible IFR flight
conditions south of Lake Ontario improving back to VFR from north
to south.
Tuesday through Thursday...mainly VFR...with localized IFR in
southern tier valley fog possible each night/early morning.


a weak pressure gradient will be in place across the lower Great
Lakes through today...with generally light winds and minimal waves
expected. A weak surface low will then push into western New York
tonight and then south of the area on Monday...and will bring a
brief period of enhanced northeasterly winds and choppy conditions
to the South Shore of Lake Ontario late tonight and Monday morning.
Following the departure of this wave...high pressure will then build
back across our region and bring a return to light winds and minimal
wave action for the rest of the week.


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




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