Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
945 am EDT Sat Jul 30 2016
periodic showers and storms will continue through the weekend until
high pressure brings the return of dry conditions for much of next
Near term /through tonight/...
a nearly moist adiabatic profile exists over the County Warning Area as of the 12z
kpbz raob with a freezing level up near 12.5 kft and thus warm
rain processes dominating the semi-unstable cloud layer. Steering
flow and shear over the area remains rather weak, thus storm
movement will be rather slow SW-NE through the day. That said, the
sounding precipitable water of 1.76 inches is rather soggy, and the presence of
a backbuilding 250 hpa jet to the north of the County Warning Area may become
problematic during the day. This places the County Warning Area in the right
entrance region of said jet with a weak 500 mb wave approaching from
the west. As a result, swerly propagation of cells is expected
during the day with resultant multiple waves of convection likely
to move neward through the area as a result. This will yield the
threat of heavy rainfall possibly moving over similar corridors at
times during the day. Localized flooding will be possible in this
setup, and it has been included in the severe weather potential statement as a result.
Deep moisture in place will keep clouds largely entrenched over
the area through the day. While morning lows were elevated
because of the clouds, they will not likely be a harbinger of a
warm afternoon. Clouds may well keep temperatures largely below
normal generally east of New Philadelphia, Ohio. Fries
Short term /Sunday through Monday night/...
shower and storm chances will continue on Sunday as the upper
trough continues to transition east and the surface low associated
with the aforementioned boundary crosses across the north. Drier
air will finally begin to move in aloft on the backside of the
trough which will bring an end to shower/storm chances by Sunday
night. Maintained a dry forecast for Monday under continued dry
northwesterly flow, but there is an outside chance of afternoon
storms as latest model runs indicate a small jet streak developing
Monday afternoon and just enough low-level moisture remaining.
May need to include mention of showers/storms in future updates if
models show continuity with this feature.
Long term /Tuesday through Friday/...
surface high pressure will build into the area from the western
Great Lakes Monday night into Tuesday. This will allow the area to
remain in cooler northerly flow even as subsidence builds. A dry
forecast will thus be maintained through mid-week.
Ridging at all levels of the atmosphere should thereafter increase
from mid-week Onward as amplification of the pattern is evident on
basically all guidance over the upper Mississippi Valley and
northern Great Lakes during the second half of the week. This
ridge and resultant low level thermal ridge should start to flop
over toward our area by Friday, which at this point looks to be
the warmest day of the next week or so, when temperatures should
push again well above normal.
Aviation /14z Saturday through Wednesday/...
general VFR is forecast through the evening with exceptions for
isolated convection which will wane with the sun. Mention will be
reserved for amendments given the declining coverage and questionable
location of cell initiation.
Given the frontal position and abundant low level moisture, expect
the return of some fog on Saturday morning, although mid level
cloudiness is expected to alleviate a widespread IFR threat. Will
hedge from previous pessimistic forecast with an MVFR mention.
Outlook /Saturday night through Wednesday/...
broad upper troughing should maintain periodic shower and thunderstorm
restriction potential through Monday.