Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1215 am EDT Sat Jul 4 2015
shower chances are expected to gradually diminish today as an
upper low pressure trough slides eastward. Building high pressure
will ensure a dry and seasonably warm Sunday...but rain chances
can be anticipated again for Monday as another upper disturbance
is forecast to encroach in upper Ohio Valley airspace.
Near term /through tonight/...
the midnight update feature precipitation probability adjustment based on
the latest radar trends as well as progress of the rain-supporting
shortwave which is moving through southwest flow aloft.
As the main trough...analyzed from Lake Erie across the lower
Ohio Valley...shift eastward during the next 18 hours...precipitation
probs will gradually diminish in the increasing subsidence and dry
advection regime. Have adjusted temperatures upward with the latest
guidance trends given expectations of improved insolation for most
counties during the afternoon...but adjustments were not decisive
and highs a couple degrees under the averages are still anticipated.
Short term /Sunday through Tuesday/...
dry...and warmer weather is then expected as high pressure builds
through Sunday. However...models now differ significantly in
depictions of Monday weather as another disturbance in flow...albeit
weak and broad...is now projected to invade from the south and
erode the ridge.
Given the inconsistency...will not hit this too hard at
moment...but the ensemble and deterministic trend can not be
ignored so forecast will include some diurnally supported chance
probability of precipitation for Monday...as well as increasing chance numbers with the
Tuesday frontal system.
The short term temperature forecast with these changes still looks warm...but
readings were tempered closer to the seasonal averages.
Long term /Tuesday night through Friday/...
the upper flow is prognosticated to flatten through much of the period.
Individual shortwaves in the flow are expected to bring periodic
chances for showers and thunderstorms. Used an ensemble based wpc
guidance to smooth out differences in individual models...with
downward adjustments to wpc probability of precipitation. Seasonally warm temperatures
Aviation /04z Saturday through Wednesday/...
a shortwave trough advancing across the region is expected to
bring periodic showers and an eventual deterioration to IFR
conditions overnight through early Saturday. Dry advection behind
the exiting trough should allow for celings to lift and
eventually scatter out later Saturday morning and early afternoon
with a return to VFR.
Outlook.../Sunday through Wednesday/...
restriction chances are expected to increase early next week with
several crossing disturbances.