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Area forecast discussion
National Weather Service Buffalo New York
338 am EDT Mon Sep 16 2019

Synopsis...
weak low pressure will bring some scattered light showers to areas
south of Lake Ontario at times through early this morning...with
this activity then gradually fading off to our southeast through the
rest of today as the low slides southeastward across Pennsylvania.
High pressure will then bring a prolonged stretch of spectacular
late Summer weather for the rest of the week...with temperatures
climbing to well above normal by late in the week.

&&

Near term /through tonight/...
through early this morning...weak low pressure over Southern Lower
Michigan will slowly sag southeastward to Western Lake Erie. This
low...an attendant surface trough/weak frontal boundary draped
across western New York...and weak spokes of shortwave energy
rotating through the mean mid/upper level trough aloft will help to
lift our moist airmass and thereby continue to generate scattered
light showers across areas south of Lake Ontario through that time.
Meanwhile further to the north...the north country will remain
removed from the effects of the surface low and will also lie within
a much drier airmass...and will therefore remain dry.

As we move through the rest of today...the weak surface wave and its
attendant surface trough/front will sag further southeastward and
across Pennsylvania...while strong high pressure and much drier air
over Quebec province will nose south into our region. This will
result in lingering scattered light showers south of Lake Ontario
gradually fading out from north to south through the rest of the
day...with widespread morning cloud cover across this same area
following suit during the afternoon. Otherwise high temperatures
will be right around normal for mid-September...with most areas
seeing highs in the upper 60s to lower 70s.

Tonight the aforementioned surface high will continue to build
across our region. This will help to scour out any leftover early
evening clouds across the southern tier...thereby leading to mainly
clear skies for the rest of the night. Coupled with light winds and
a much drier airmass featuring dewpoints in the 40s...this should
lead to excellent conditions for radiational cooling...thereby
allowing overnight lows to fall to the lower to mid 40s across the
north country and to the mid to upper 40s in most other locations...
with only the immediate lakeshores failing to drop below 50 degrees.

&&

Short term /Tuesday through Wednesday night/...
this period will be dominated by an anomalously strong 500 mb ridge that
will amplify while slowly drifting east across the upper Great Lakes
and Ohio Valley. Having this strong ridge immediately upstream from
our forecast area will guarantee that fair dry weather will be in
place through this period. For the remainder of the time frame.
Meanwhile...temperatures for both Tuesday and Wednesday will average
above normal. As for some day to day details...

A large surface high centered over eastern Quebec Tuesday morning
will gradually extend to the southeast across the lower Great Lakes
to the Ohio Valley Tuesday afternoon and night. This will insure
beautiful weather for Tuesday with sun filled skies helping
afternoon temperatures reach 70 to 75 for all but the highest
elevations and portions of the north country. Another starlit night
will then 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 (positive
tilt) and open the door for a little more noticeable warm advection
to 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 Sunday/...
..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 (at least thru
sat).

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 mid to upper 70s Thursday...with 80s
expected for Friday through Sunday.

While we can count on dry weather thorugh at least Saturday...a
large stacked storm system over central Canada during the weekend
will eventually push a Pacific based cool front through our region.
There is some uncertainty as to whether this front will come through
on Sunday...or Sunday night-Monday...but will include at least the
chance for some showers as we end the weekend.

&&

Aviation /08z Monday through Friday/...
through early this morning...weak low pressure over Southern Lower
Michigan will slowly sag southeastward to Western Lake Erie. This
low...an attendant surface trough/weak frontal boundary draped
across western New York...and weak spokes of shortwave energy
rotating through the mean mid/upper level trough aloft will help to
lift our moist airmass and continue to generate scattered light
showers across areas south of Lake Ontario through that time.
Meanwhile further to the north...the north country will remain
removed from the effects of the surface low and will also lie within
a much drier airmass...and will therefore remain dry.

In terms of flight conditions through the above time frame...the
combination of further moistening of the low levels and a burgeoning
northeasterly upslope flow to the north of the surface boundary will
result in MVFR/embedded areas of IFR conditions continuing to spread
southward across areas of Lake Ontario...while the north country
remains predominantly VFR aside from some patchy lower clouds and
fog...which will affect the kart terminal at times through daybreak.

During the rest of today...the weak surface wave and its attendant
surface trough/front will sag further southeastward and across
Pennsylvania...while strong high pressure and much drier air over
Quebec province noses south into our region. This will result in
lingering scattered light showers south of Lake Ontario gradually
fading out from north to south through the rest of the day...with
widespread morning cloud cover across this same area following suit
during the afternoon. As a result we can expect an initial mix of
MVFR and IFR conditions south of Lake Ontario to gradually improve
back to VFR from north to south through the course of the day...
with this improvement taking place toward sunset across the southern
tier. Meanwhile...the north country will be VFR once any patchy fog
and/or lower clouds dissipate by mid morning.

After that...the aforementioned surface high will provide our area
with mainly clear skies and predominantly VFR conditions tonight...
with just some localized valley fog/IFR developing across the
southern tier overnight.

Outlook...
Tuesday through Friday...mainly VFR...with localized IFR
in southern tier valley fog possible each night/early morning.

&&

Marine...
a weak surface low over lower Michigan will push southeastward to
Western Lake Erie by early this morning...then south of the lower
lakes region through the rest of today. While this system will help
induce a brief period of enhanced northeasterly winds and choppy
conditions from Ripley to Dunkirk on Lake Erie and also along the
southwestern shore of Lake Ontario this morning...conditions will
remain below Small Craft Advisory levels. 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.
Marine...none.

&&

$$

Synopsis...jjr
near term...jjr

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