Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1216 PM EDT Wednesday Oct 7 2015
seasonably warm and dry conditions will remain until a cold front
brings showers and cooler temperatures Thursday night and Friday.
Near term /through Thursday/...
visible satellite imagery reveals a rapidly rising stratus layer
over most of western Pennsylvania that is quickly being eroded
around the edges as dry air from aloft entrains rapidly with
increasing insolation going into the early afternoon hours. Most
of the stratus layer actually is looking a bit more cumuliform as
well...which should help to mix dry air even within the stratus
covered area as well. That said...all areas are expected to go
partly cloudy shortly...and likely rapidly warm into the 70s
thereafter this afternoon.
Surface high pressure settles over the northeastern reaches of the
County Warning Area overnight. With little boundary layer advection and dewpoints
still likely to be near 50 degrees...this seems to set the stage
for more fog formation overnight. Fog was added to the forecast to
account for this as low temperatures do seem poised to fall toward
the dewpoints overnight toward morning.
Low level flow will slowly turn toward the southwest on Thursday
as the next short wave trough starts to drop into the Great Lakes.
All of the lift and moisture associated with it will still be
hanging back to our northwest through the day.
However...increasing southwesterly flow ahead of it should allow
for a bit of increased mixing and modest warm advection to allow
high temperatures to run well into the middle and even a few upper
70s across the area on Thursday. Fries
Short term /Thursday night through Saturday/...
ridging will transition over the region Thursday resulting in
continued dry conditions and a slight increase to temperatures.
Maximum daytime temperatures are forecast to range from 5 to 8 degrees
above climatology norms. Clouds will be on the increase by Thursday
evening as a middle level shortwave and an associated cold front
approach. Shower chances will increase from west to east Thursday
night with likely probability of precipitation west of the ridges daybreak Friday. Cat
probability of precipitation for Friday as front progresses across the region. Middle level
trough will deepen in the southern stream Friday night and slow the
fronts exit Friday evening...with likely probability of precipitation in the southeast
ridges and chance probability of precipitation elsewhere. Showers will end overnight as
surface ridge axis slides across the Ohio Valley into Saturday
with cooler temperatures.
Long term /Saturday night through Wednesday/...
high pressure is expected to bring dry weather through early next
week. Broad upper troughing is prognosticated across the eastern Continental U.S.
Monday night into middle week. A couple of weak shortwaves advancing
through the trough should bring an increase in clouds and only
slight chances for showers. Followed close to wpc ensemble based
guidance through the long term period. Other than above average
temperatures on Monday...seasonally cool temperatures are expected.
Aviation /16z Wednesday through Sunday/...
stratus will quickly break up with just some cumulus remaining
this afternoon. IFR fog is again likely locally tonight with very
light surface flow and still elevated dewpoints. This will breakup
rather rapidly late Thursday morning as increasing southwesterly
flow advances toward the area ahead of the next system. Fries
Outlook...Thursday through Sunday...
restrictions are possible with a crossing cold front Thursday night