Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
908 PM EDT Friday Aug 1 2014
temperatures will move to near average with chances for showers
and thunderstorms through Sunday. Dry and mild conditions to
return by the beginning of next week.
Near term /until 6 am Saturday morning/...
thunderstorm activity has been eradicated from our environs...and
shower activity has waxed and waned substantially in the past few
hours. The remnant showers continue to cling to life along and
ahead of a westward trudging outflow boundary that has moseyed all
the way toward the Pennsylvania/Ohio border at this hour. As the
sun has already bid US adieu this evening...instability should
continue to dwindle from its already paltry levels...and any
additional activity tonight should be at best isolated. Probability of precipitation were
summarily wound down across the vast majority of the area as a
result. The lone exception to this was toward morning over the
ridge areas as some moisture and additional lift seem to be poised
to advance northward into Saturday morning. Fries
Short term /6 am Saturday morning through Monday/...
shortwave digging through the upper trough will make it's approach
late on Saturday. While the deepest moisture will remain shunted by
the higher terrain to the east...the approaching shortwave should
provide enough lift to set off showers and storms across most of the
forecast area by Saturday afternoon. Since the low-middle level flow
will remain rather weak...and BUFKIT soundings have very unimpressive
instability values...do not anticipate a severe threat. Actually
question the extent of thunder as cloud cover could further limit
destabilization. Precipitable water values will also remain under 1.5 inches...so
heavy rain is not anticipated except in any slow moving storms.
Shortwave will take its time crossing the region...maintaining the
chance for showers and a few storms into Sunday. By Monday...most of
the moisture will be well east of the region...with subsidence
taking place further west. Will keep slight chance probability of precipitation in the
forecast for the ridges however.
Temperatures were a blend of mex/met values through the period.
Long term /Monday night through Friday/...
upper trough will remain settled over the eastern Continental U.S. Through the
bulk of the long term...shifting eastward by late in the period.
Models have a weak cold front dropping southward out of the Great
Lakes late Tuesday into Wednesday but at this point it looks rather
moisture starved. After this...the model solutions diverge. Opted to
maintain low chance probability of precipitation through much of the period...increasing
chances late as the low level flow turns more southwesterly.
Temperatures will remain right around seasonal averages through the
Aviation /01z Saturday through Wednesday/...
shower coverage has dropped significantly during the late
afternoon hours...and duj appears to be the only site left that
could see some rain in the near term. Cannot rule out an isolated
shower overnight at any taf site. Have gone more pessimistic with
latest taf issuance in late night flight categories. Previous
forecast was based on the expectation that clouds would remain
most of the night and only a slight visibility reduction would
occur. Current thinking is that skies will clear out more than
expected tonight...which would allow for further visibility
reduction. As a result...have dropped visibilities from 3-5 miles
to 2-3 miles...and guidance suggests widespread IFR conditions.
Have decided to make a downward trend with visibilities...and not
bottom out the forecast until after sunset to see how cloud cover
develops. As for Saturday...did not have enough confidence in
coverage of thunderstorms to keep thunderstorms in the vicinity mention in tafs...but
replaced it with vcsh mention. Winds throughout the taf period are
expected to remain less than 10 kts.
Outlook.../Saturday night through Wednesday/...
a low pressure system could bring restrictions through the balance
of the weekend.