Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1152 PM EDT Friday may 29 2015
the remainder of the evening will remain relatively quiet with
chances of thunderstorms returning to the region Saturday
afternoon through Sunday.
Near term /through Saturday/...
clouds from earlier convection are dissipating rapidly late this
evening...with notable clearing evident on satellite imagery as
the warm front that lifted northward earlier this afternoon now
having passed all the way to the shores of Lake Ontario. This has
allowed for subsidence to reestablish itself and work to eradicate
cloud cover rapidly after sunset. That said...rainfall across the
area earlier has allowed for abundant low level moisture and high
dewpoints to settle into the area. This should preclude strong
diurnal temperature falls through the morning hours.
Deep layer southwesterly flow continues into Saturday.
However...with the main short wave trough still well to our west
and the front boundary ahead of it focusing all low level
convergence well to our north across lower Michigan and the lower
Great Lakes...it would seem convection should be on a fairly
limited scale due to warm temperatures aloft. However...typical
afternoon showers/thunderstorms may still occur simply due to the
warm/humid air mass and strong low level lapse rates due to ample
early day insolation. Sky grids have been reduced greatly through
the morning and limited to partly cloudy all day to account for
warm air aloft. Also...rain/thunderstorm chances have likewise
been limited most to the afternoon owing to a lack of lifting
mechanism through the day. Fries
Short term /Saturday night through Monday/...
another weak shortwave is prognosticated to advance across the region
Saturday with some scattered showers and storms expected. A cold
front should slowly drop south across the area Saturday night
through Sunday bringing better shower and thunderstorm chances.
Generally used a blend of the GFS and sref for positioning of the
front and precipitation timing. Shear and instability are prognosticated to
remain relatively limited with warm air aloft...precluding a
widespread severe weather threat. The front is expected to be
along the PA/WV border later Sunday...with a surface wave prognosticated
to track along it Sunday evening. The wave should gradually shift
east of the area Monday allowing for decreasing precipitation chances.
Temperatures should start out well above average...with a decrease
to near seasonal average numbers by Sunday and Monday using the
latest gridded MOS and sref data.
Long term /Monday night through Friday/...
have slowed the ending of showers a bit into Tuesday for the
southeast ridges as models are a bit slower with trying to develop
and shift east wave of low pressure moves along cold front just
south of region. Otherwise little change from wpc forecasts as dry
surface high pressure builds in across the region through middle
week. By late week heights rise aloft and surface ridge moves off
the East Coast...allowing for warmer temperatures and increasing
Aviation /04z Saturday through Wednesday/...
VFR conditions through the period with thunderstorms possible
again tomorrow afternoon through Sunday as a cold front slowly
transitions across the region from the north. No widespread
restrictions are anticipated until after frontal passage Sunday evening.
Outlook.../Saturday night through Wednesday/...
restrictions will be possible through the weekend mainly during
the afternoon and evening...becoming more likely Sunday evening.