Area Forecast Discussion
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FXUS61 KPBZ 292334
Area Forecast Discussion
National Weather Service Pittsburgh PA
634 PM EST Tue Nov 29 2016
Several crossing disturbances will result in periodic rain
chances in the forecast through the mid week.
.NEAR TERM /THROUGH WEDNESDAY/...
520pm update...made some minor adjustments to timing for the onset
of rain, in line with the latest hires model guidance. Evening
cloud cover was also adjusted using latest satellite trends.
Temperatures were update with a blend of hires guidance.
Previous discussion follows...
Another surface low originating near Texas will be pulled up the
Mississippi Valley and along the Ohio Valley late tonight. This
will again bring increasing clouds along with organized rain that
will last through Wednesday. The rain will be supported by deep
moisture, ascent along the deformation zone, and low level jet
support is expected with it`s passage.
Location of primary rain band will be dependent on the exact track
of the low and the aforementioned deformation zone. Latest
NAM/GFS/SREF trend the low further west than the previous
forecast, bringing the best rain chances almost directly over
Pittsburgh and through the heart of the forecast area. Have
adjusted PoPs to account for this trend, but overall, the forecast
remains largely the same. Everyone should see at least some rain
from late tonight through Wednesday.
Temps will remain well above average tonight ahead of the rain.
The arrival of the low and associated cold front make Wednesday
high temps a little more difficult, but they will remain above
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
Model differences remain with regard to the rapidity of the exit
of precipitation from the area on Wednesday night. Likewise, upper
troughing starts to move farther eastward into the Great Lakes
region with the frontal passage on Wednesday night, low level flow
really fails to turn NW immediately. Thus, drier air should move
into the area with the best chance for any showers of rain or snow
behind the front remaining mostly north of I-80.
Low level flow starts to get a smaller northerly component by
Thursday night into Friday as the upper low continues to migrate
slightly farther east. This may allow for a few rain and snow
showers to start to develop into the ridges, as well.
Temperatures will trend decidedly downward behind the frontal
passage on Wednesday night. However, it will really only get us
cool enough to allow for mixed rain and snow showers with little
accumulation expected most anywhere. Fries
.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Ridging will likely move closer and closer to the area through the
weekend with low level flow gradually losing any northerly
component. This should allow for showers to wind down with drier
air again returning to the CWA.
After the weekend, model solutions start to diverge with regard to
potential activity crossing the area Sunday night into Monday.
They also diverge in terms of thermal profiles when any potential
activity does. A blend of models was used in this portion of the
forecast with very low confidence as a result.
From Monday onward, model and ensemble solutions actually start to
converge upon more amplified ridging developing over the area as a
deep low starts to develop in the southern Rockies. This should
allow temperatures to head back upward again from the early to the
middle part of next week as rain again develops. Fries
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --VFR conditions to begin the forecast period with high clouds
streaming out ahead of the next low pressure system, which is
approaching from the southwest. Expect deterioration to MVFR and
IFR in the hours surrounding sunrise as rain spreads in. These
restrictions will hold into the afternoon hours, with the passage
of a frontal boundary allowing for some slow improvement after
Winds will remain light out of the south and southeast tonight.
Models show a low level jet passing to the southeast of Pittsburgh
mainly between 12Z and 18Z. While surface winds will gust to
between 20 and 25 knots at the surface in this area, there is
also a threat of low level wind shear with strong winds at the top
of a fairly shallow inversion. Will include LLWS in the MGW and
LBE TAFs, with the possibility of westward expansion depending on
the track of the low level jet.
Periodic restrictions are again likely, especially over FKL and
DUJ, as colder air moves back over the region during the latter
half of the week.
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