Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Pittsburgh PA
128 am EDT Thursday Jul 24 2014
a scattered shower will be possible over the far south today...as
a cold front gets hung up in the ridges. Otherwise dry weather and
comfortable conditions into Saturday.
Near term /through today/...
only minor changes to overnight period.
Cold front has made it into the middle-Atlantic region. The trailing
dewpoint boundary is hung up over the far south. A large area of
stratocu has filled in over the area with the colder air aloft. It
appears that these lower clouds will stubbornly hold on through
the night and a good portion of the day. Drier air will nudge its
way in from the northeast...which will allow for a decrease in
cloud cover toward the south. Cloud forecast will be tricky...
forecast soundings are showing quite a difference between cloud
cover in the northern half compared to that over the south.
Soundings want to allow for drying across most of the region
during the morning...then quickly re-saturate the lower levels by
afternoon. If the soundings are in line...it will be pretty cloudy
over the southern half during the afternoon. This will also effect
temperatures for the day.
Latest model solutions are showing the higher dewpoints lingering
over the far south and ridges into the afternoon...waiting for a
push from a shortwave trough. With the main front stalled over the
middle-Atlantic and the dewpoint boundary trapped near the ridges...
models pool moisture along the ridges through much of the day.
This setup is allowing for modest instability in these
locations...which will require the inclusion of probability of precipitation into the
afternoon. This works well with the aforementioned saturation in
the lower levels.
Short term /tonight through Saturday/...
trough will eventually evacuate the moisture over the south during
the evening. The risk for showers will end and a very comfortable
night will be on tap.
High pressure at the surface and northwest flow aloft will provide
a comfortable Friday with plenty of sunshine.
A series of shortwaves will move through Saturday in the northwest
flow aloft. As the flow in the upper levels remains out of the
northwest...flow at the lower levels will back to the southwest.
This will allow humidity to rise on Saturday. With the lift aloft
and the increased instability...shower/storm chances will
increase Saturday. At this point...storm activity may be
suppressed by cloud cover...but will leave in the mention...
particularly in the afternoon.
Long term /Saturday night through Wednesday/...
flow in the upper levels will become more zonal Saturday night.
Models are hinting at an mesoscale convective system developing over the upper Midwest
late Saturday afternoon and quickly heading eastward Saturday
night. If this complex does develop...still a bit early to
determine its exact track...it will move across Lake Erie. This
would mean that the area could see activity from this complex
Saturday night. A cold front will trail the mesoscale convective system and spread out
across the region into early Sunday morning.
Another surface wave will move along the stalled surface front
Sunday...meaning a good chance for widespread showers and storms.
Shower threat continues on Monday as another front moves through.
Noticeably cooler air for the end of the long term.
Aviation /05z Thursday through Monday/...
appears MVFR stratus in cold advection will hang on overnight in low
level northerly flow. Ceilings should gradually lift toward daybreak and
become broken VFR after 13-15z. With colder temperatures aloft expect VFR broken
ceilings until late afternoon when subsidence with surface high settling
across region will clear skies. Near calm and clear tonight.
Outlook.../Friday through Monday/...
restrictions possible at times later Saturday and Sunday as low
pressure approaches. A cold front will continue possible