Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
418 am EDT Wednesday Jul 23 2014
a cold front will bring showers and storms to the area today and
through the evening hours. Cooler and drier air for the rest of
Near term /until 6 PM this evening/...
a cold front will rush through the region today. Front will
receive and nice push from a strengthening shortwave trough which
will swing in behind the surface boundary this afternoon. Most of
the shower and storm activity will be right along the front and
behind in the vicinity of the trough. Atmosphere will quickly
destabilize as the front moves through. Because of the timing of
frontal passage...the southern half of the area will experience
higher instability levels with surface based cape of 1500 to 2000
j/kg and a lifted index close to -4. Would think that if any
stronger activity develops...it would be over the south. Shear
values are not impressive only around 20 to 25kts...and with front
clearing the entire area by 20z...it will not cross at the most
Even though the front will pass in the early part of the
afternoon...will need to keep in probability of precipitation behind the front with the
passage of the strong shortwave.
Short term /6 PM this evening through Friday/...
it will take most of the evening for the shortwave to exit the far
south. This will necessitate leaving in probability of precipitation across the southern
half through the evening. Atmosphere will be stabilizing so expect
the thunderstorm threat to diminish in the evening.
Another upper level disturbance will cross on Thursday...by this
time most of the moisture will confined to locations near the
Mason-Dixon line. Will leave in the mention of showers there until
the trough passes late Thursday afternoon.
Cooler and drier air for the entire region Friday with surface
high moving in and the upper level flow becoming more zonal.
Long term /Friday night through Tuesday/...
low confidence forecast for the beginning of the long term period.
Models exploring some different options with a shortwave trough
that will cross the area sometime on Saturday. This part of the
forecast will need to be refined once model run to run becomes
The next system will bring showers and storms to the area Sunday
and Monday and much cooler air for the end of the long term.
Aviation /08z Wednesday through Sunday/...
a period of MVFR fog before daybreak expected with clear
skies...although mixing in the low level boundary layer looks to
preclude any significant IFR.
By late morning an approaching cold front from the Great Lakes will
bring scattered showers and storms from northwest to southeast
across the region. For now MVFR in showers with vicinity thunder still
looks good and can be refined in later terminals if need be. Winds
will become west to southwest ahead of the front and shift to
northwest near 12kts with frontal passage.
Outlook.../Wednesday through Sunday/...
general VFR Thursday into Saturday as high pressure returns to the
area. Restrictions possible later Saturday and Sunday as low