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Area forecast discussion 
National Weather Service Buffalo New York
1102 PM EDT Friday Jul 31 2015

a weak trough will cross the region overnight with widely scattered
showers and thunderstorms. Widely scattered showers and
thunderstorms are possible again Saturday afternoon and Sunday
afternoon but the vast majority of the time is expected to be rain
free. A stronger front will cross the area Sunday night and Monday
with a better chance of showers and thunderstorms. This front will
usher in a much cooler airmass for much of next week.


Near term /through Saturday/...
a weak trough will cross the region overnight. Radar mosaic at 11pm
shows widely scattered showers and isolated thunderstorms working
across western and north-central New York. The back edge is showing
up near mississauga Ontario along the leading edge of the surface
trough. As the trough passes west to east across the forecast expect
shower and thunderstorm activity to also taper off.

Partly sunny skies are then expected Saturday morning before another
weak trough is expected to cross the area during the afternoon.
Temperatures will be cooler aloft on Saturday...and the subsequent
steep low/middle level lapse rates and sufficient low level moisture
will produce a widespread area of congested cumulus during the late
morning and afternoon. Most areas inland from the lakes will trend
towards mostly cloudy skies with widely scattered showers and
isolated thunderstorms during the afternoon in response to lake
breeze convergence and weak ascent from the approaching middle level
trough. Stable lake shadows will keep areas east of both lakes
sunnier and drier through at least middle afternoon...although the
approach of the middle level trough may force a shower or two through
the stable lake shadows by late afternoon or early evening.

Temperatures will be a little cooler on Saturday with 850mb temperatures
around +11c. Expect highs in the upper 70s to around 80 at lower
elevations and middle 70s across higher terrain. It will become breezy
again east and northeast of lakes Erie and Ontario with gusts around
30 miles per hour during the midday and afternoon.


Short term /Saturday night through Sunday night/...
no changes to the short term forecast this evening.

Previous discussion...
Saturday night a shortwave will be passing through the base of an
upper level low...shifting the axis of lower heights eastward. A
few remaining showers or perhaps a thunderstorms will be possible
early Saturday evening...but with waning daytime instability and
the rising heights aloft expect the bulk of the night to be dry.

Sunday will start dry as southwest flow is found over the eastern
Great Lakes region...this flow between an area of high pressure over
the Tennessee Valley and southern Appalachians...and low pressure
near Hudson Bay. This southwest flow will bring warmer air
northward...along with a degree or two rise in dewpoints. Daytime
instability may trigger a shower or thunderstorm...especially on lake
breeze boundaries...but lacking a good forcing mechanism dont expect
too many storms. Sunday will also be breezy as areas downwind of the
eastern Great Lakes on a southwest wind may gust 25 to 30 miles per hour
through the afternoon hours.

Sunday night another shortwave trough will round the large Hudson
Bay upper level low. This shortwave is a little more potent and lift
from this feature/nearing of an upper level thermal gradient and
building moisture ahead of a cold front will bring increase chances
for showers and thunderstorms late overnight Sunday...especially
over far northwest areas of the Niagara Frontier and the Saint Lawrence

Temperatures will remain seasonable through this time period.


Long term /Monday through Friday/...
for this time period the long range models of the GFS/European model (ecmwf) are
in good agreement with placement of an upper level low over
eastern Canada...and a second upper level low near the British
Columbia coastline. A ridge of high pressure will be found between
these two upper level lows...though the ridge will likely remain
weak and farther west enough to not be able to dislodge the upper
level trough over eastern Canada. Though this upper level trough
will retreat some...its general presence will spell an extended
period of cool time for the northeast.

Monday will be the last of near-to slightly above normal day
temperature wise as the axis of the upper level trough remains just
to our west. Through the day this axis will swing across the eastern
Great Lakes region driving a surface cold front that will trigger
showers and thunderstorms. This activity will end from west to east
through the overnight hours as the surface cold front eventually
clears the region. The GFS is depicting a fair amount of instability
with SBCAPE values edging over 1000 j/kg over the Genesee Valley and
Finger Lakes region. A 40 knot low level jet producing low level convergence
may be able to organize a few of these thunderstorms into strong

Tuesday through Friday will be cool with chances for a rain shower
each day. Multiple vorticity maxima rotating through this upper
level trough...combined with day time instability may bring a few
showers to the Buffalo County warning area. With lake temperatures now in the +21 to
+23c range...and 850 hpa dropping down to +6 to +10c...there may
even be some lake enhancement to these showers downwind of both
lakes Erie and Ontario.

Highs Tuesday through Friday will generally be in the upper 60s to
low-middle 70s...about 5-10 degrees below normal...while overnight lows
will run in the 50s. Some warming is possible Friday as the upper
level low retreats northward some and a warm front nears the region.


Aviation /03z Saturday through Wednesday/...
widely scattered showers and isolated thunderstorms are observed on
radar at 11pm shifting across western and north-central New York as
a weak trough crosses the eastern Great Lakes. Any heavier showers
may contain brief/local MVFR or IFR conditions...but VFR will
prevail the majority of the time.

Any scattered convection will end overnight with at least partial
clearing for Saturday morning. Extensive diurnal cumulus are then
expected to develop from late morning through the afternoon on
Saturday with most areas going broken by midday. Stable lake shadows
will keep skies more clear east of both lakes. Widely scattered
showers and isolated storms will develop during the afternoon mainly
along and inland from the lake breezes...but again coverage should
remain sparse.

Sunday and Monday...mainly VFR with widely scattered showers and
Tuesday...mainly VFR with a chance of a few light showers.
Wednesday...mainly VFR with a slight chance of a light shower.


another weak trough and decent pressure gradient will
bring another round of Small Craft Advisory conditions on Saturday
to the eastern ends of both lakes Erie and Ontario.

This same basic pattern will continue through the weekend with winds
dropping off some Saturday night and early Sunday before increasing
to near Small Craft Advisory conditions on both lakes later Sunday.
The Small Craft Advisory conditions may last Sunday night into
Monday as a stronger cold front crosses the region.


Buf watches/warnings/advisories...
New York...none.
Marine...Small Craft Advisory from 1 PM to 11 PM EDT Saturday for
Small Craft Advisory from 1 PM to 8 PM EDT Saturday for
Small Craft Advisory from 10 am to 11 PM EDT Saturday
for loz043>045.



near term...Hitchcock/Smith
short term...apffel/Thomas
long term...Thomas

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