Scientific Forecaster Discussion
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Area forecast discussion...updated
National Weather Service Pittsburgh PA
732 PM EST Sat Feb 25 2017
cooler temperatures will again be replaced by well above normal
temperatures mid-week. More wintry conditions look to return
late in the week.
Near term /through Sunday/...
730pm update...expanded the pops southward this evening
by around one tier of counties over eastern Ohio and western
PA. The leading edge of the real cold air is allowing for the
creation of scattered snow showers and flurries as the dendritic
zone is forced lower in the atmosphere. With the upsloping
influence over western PA, some of this light snow could
strengthen just a bit allowing for iso to scattered snow showers
this evening. This feature will continue across the rest of the
region where there are pops this evening. Later tonight, the
snow showers will depend more on streamers from the lakes and
the real upsloping effect over the ridges.
further upstream, a solid patch of clouds and scattered showers
can be found over central Ohio to Indiana. These will shift
eastward this evening as the upper- level low approaches.
Expecting shower chances to increase through the evening, per
latest hi- res model guidance.
Scattered rain showers will changeover to snow showers as
temperatures continue to descend through the evening. In
general, less than an inch is expected across northern counties
and into the mountains. Little to no accumulation is expected
elsewhere. Building high pressure will end precipitation chances
overnight with the ridges and locations along and north of I-80
the last holdouts.
Winds and associated gusts are increasing, in the enhanced cold
advection. Wind in the highest elevations could approach
advisory criteria towards dusk. This will bear further
Sunday will feature more docile weather as high pressure at the
surface builds in. This will slowly erode cloud cover, leaving
much sunnier conditions. Temperatures Sunday will moderate to
near normal values.
Short term /Sunday night through Tuesday/...
surface high pressure will begin to shift eastward early in the
short term period. This will mean dry and relatively clear
conditions will quickly be replaced by increasing cloud cover on
Sunday night. With a fairly linear jet streak parked directly
overhead the County Warning Area slowly beginning to migrate eastward into
Monday, a weak 500 mb vort looks to traverse the Ohio Valley on
Monday. Weak warm advection ahead of it may be just enough to
generate a shower or two through the day Tuesday. Some
soundings indicate that a brief window of snow may be possible
at the onset due to wide surface dewpoint depressions and low
wet bulb zero heights, however very light qpf expectations
combined with warm advection and no support for below freezing
temperatures should preclude any possibility of accumulation
should this occur.
With the northward migration of a warm front through the area
on Tuesday, temperatures during the short term look to return to
above normal yet again. Fries
Long term /Tuesday night through Saturday/...
a brief dry interlude follows th weak system from Tuesday
before much higher pwats follow for later Tuesday night into
Wednesday night. A couple of successive waves look to pass the
region in deep southwesterly flow. Some heavier rainfall may be
possible with these given precipitable water values running up toward 1.3
inches and a nicely couple jet structure to accentuate ascent.
A trailing cold front will pass the area on Thursday. This will
set temperatures into a free fall with model and ensemble
consensus 850 mb temperatures falling into the negative teens
celsius. This should bring lake and upslope snows back into the
picture. Additionally, some model indications exist of a weak
system dropping through the Ohio Valley on Friday in the colder
air. This could end up being a modest snow maker somewhere in
the region depending upon its track.
The extended forecast was generally favored colder than the
superblend guidance from Thursday night through Saturday due to
the amplitude of the pattern and magnitude of cold air set to
advect into the region. Fries
Aviation /01z Sunday through Thursday/...
westerly wind gusts of 25-35 knots will slowly subside with
time, falling to 20 knots or less overnight for the most part.
Ceilings will generally fall into the MVFR or low VFR range
through the night and past sunrise on Sunday. Scattered snow
showers, particularly north of I-80 and along the ridges, may
produce brief localized IFR restrictions tonight.
VFR conditions will take hold at all terminals by late morning
Sunday as high pressure builds in. Winds will remain from the
west, but fall in the range of 10 to 20 knots.
occasional restrictions are again possible as the unsettled
weather pattern is maintained for the first half of the week.