Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Buffalo New York
1046 am EDT Wednesday Jul 29 2015
after one more hot day today...a cold front will cross the region
later tonight and early Thursday while bringing some scattered
showers and thunderstorms...followed by cooler and less humid
conditions for the end of the work week and upcoming weekend.
Near term /through tonight/...
during the course of today...surface high pressure initially
draped across New York state will slide east to the Atlantic
coastline... while the axis of its corresponding upper level ridge
builds directly overhead. The resulting combination of rising
heights/subsidence aloft and a light to modest southwesterly flow
at the lower levels will help bump 850 mb temperatures up to the +19c to
+20c range...their warmest levels of the week. With fairly
plentiful sunshine expected...this should result in afternoon high
temperatures reaching into the lower 90s across those lower
elevation areas away from any lake influences... with a few of our
normal warm spots in the Genesee Valley and Finger Lakes /such as
Dansville/ likely reaching the middle 90s. Elsewhere readings should
stay confined to the 80s across the higher terrain and closer to
the lakes...including at Buffalo/Watertown where an earlier-
developing southwesterly flow off the lower lakes may keep highs
from reaching 90 in spite of the warmer temperatures that will be
in place aloft. Along with the higher temperatures will also be a
modest bump in humidity levels as dewpoints should reach into the
lower to middle 60s today...though heat indices should still remain
confined to the lower to middle 90s...or safely below heat advisory
Otherwise...expect largely dry conditions to continue to prevail
today under the building upper level ridge. While an isolated pop-
up shower or thunderstorm cannot be totally ruled out in this kind
of airmass... at this point feel that the nam12 is greatly
overdone with both its surface dewpoint forecast /a typical bias/
and consequent depiction of convection blowing up along the Lake
Erie lake breeze boundary late in the day. With this in
mind...have leaned toward a consensus of the rest of the 00z
guidance suite...and have kept forecast probability of precipitation below mentionable
levels through this evening.
As we get into tonight...generally dry and quiet weather should
continue through the evening hours...before low pressure over
northern Ontario eases its trailing weak cold front into the
region overnight. With this boundary being accompanied by only
limited moisture and practically no upper level support...expect
its associated convection to remain fairly scattered in
nature...with the unfavorable time of the diurnal cycle and
unimpressive shear profiles also greatly limiting any potential
for stronger storms. Otherwise we can expect the most sultry night
of the week...with overnight lows struggling to drop below the
upper 60s to lower 70s in most places...and surface dewpoints
rising into the middle and upper 60s.
Short term /Thursday through Saturday night/...
Wednesday night's cool front will be exiting the north country as
we move into Thursday morning taking with it the last of any
remaining showers and leaving sunny and somewhat milder weather in
it's wake as a piece of an expansive surface high over the Midwest
settles across the lower Great Lakes. The cooler air behind the
front will mean a return to more seasonable readings ranging from
the upper 70s downwind of the lakes to the middle 80s in the warmer
spots of the Genesee Valley and north of The Finger lakes.
Readings here will be boosted a couple of degrees owing to
downsloping southwesterly flow...which will be quite brisk as the
gradient tightens between a deep surface low over James Bay and
the aforementioned high building in from the Midwest. In fact it
will be quite breezy east-northeast of lakes Erie and Ontario where winds
could gust to around 25 miles per hour Thursday afternoon.
Skies will remain clear and winds should slacken somewhat
Thursday night as high pressure remains in place..however flow off
the lake will keep lows in the middle 60s across the Niagara Frontier
with lower 60s elsewhere and upper 50s across higher terrain of
the southern tier and Tug Hill plateau.
Broad upper level troughing will become established across the
Great Lakes as a large upper level low stalls out over Hudson Bay.
With plenty of sunshine and cooling temperatures aloft as the
trough become established...cannot rule out a few poorly organized
pop-up showers or thunderstorms...particularly across the north
country which will be deeper into the cooler air aloft.
The better chance for showers and thunderstorms will be on
Saturday as a shortwave moving through the base of the longwave
trough crosses the lower Great Lakes. Current model timing of this
feature brings it across the forecast area from late morning and
into the afternoon hours...suggesting that convection should be
widespread across the forecast area...particularly if the system
can tap into moisture advecting out of the Ohio Valley. There is a
better potential for strong and possibly low-end severe storms
with this as model profiles are currently indicating 0-6km shear
pushing 30kts and will mention this in the severe weather potential statement.
Convection should move off to the east and dissipate Saturday
evening as the shortwave passes by with some clearing as weak
surface based ridging returns to the region. Regarding
temperatures Friday and Saturday...the aforementioned troughing
aloft will translate to cooler surface readings across western and
north- central New York with highs right around average for middle-
Summer withs in the upper 70s to lower 80s and lows in the upper
50s to middle 60s. Slightly cooler air associated with saturday's
shortwave may drop readings a few degrees cooler Saturday night
with lows in the lower 60s near the lakes with cooler temperatures in the
middle 50s across higher elevations.
Long term /Sunday through Tuesday/...
looking at the latter half of the weekend and into next
week...the longwave trough looks to become firmly re-established
from the upper Midwest to the Great Lakes and the northeast. This
will keep temperatures seasonably mild with highs in the upper 70s
to around 80 in most areas with lows ranging from the middle 50s
across higher elevations of the southern tier and the Tug Hill
plateau to the lower 60s near the lakes. A series of shortwaves
rotating through the base of this trough will bring alternating
periods of showers and thunderstorms with fair weather in between
shortwaves...however timing these features this far out is
unrealistic with models displaying disagreements on the specific
timing. Thus will stick with generic broadbrush chance probability of precipitation for
the time being. Looking farther out...this pattern looks to stick
around through the coming week as the longwave trough will only
slowly drift east from Hudson Bay across Quebec through the week.
Aviation /15z Wednesday through Sunday/...
widespread VFR conditions will continue to prevail through this
evening as high pressure over New York state slowly drifts east to
the Atlantic coastline.
After that...a weak cold front will push across the western two
thirds of the area during the latter half of tonight. The front
will be accompanied by scattered showers and thunderstorms that
could produce brief/localized reductions in cig/vsby...with
conditions otherwise expected to remain VFR.
Thursday...a chance of morning showers and thunderstorms across
the eastern Finger Lakes and north country...otherwise VFR.
Friday through Sunday...mainly VFR with isolated to scattered
showers and thunderstorms.
expect light to modest winds and negligible waves to persist
through this evening across the lower lakes region as high
pressure over New York state slowly drifts east and eventually
moves off the Atlantic coastline. A weak cold front will then
bring the chance for some showers and thunderstorms overnight into
early Thursday morning... with locally higher winds and waves
possible in/near any convection...and relatively benign
conditions persisting elsewhere.
Following the passage of the cold front...a moderate westerly to
southwesterly flow will set up across Lake Erie during Thursday...
when winds and waves may approach/reach lower-end advisory
criteria. After that...high pressure over the Ohio and Tennessee
valleys will gradually ridge northeastward toward the lower lakes
during the remainder of the work week...resulting in a modest
southwesterly to westerly flow that should remain below advisory