Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
947 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 /until 6 PM this evening/...
945 am...the main rain shield has moved east with only a few
lingering rain showers in the far east. Still expect a few to redevelop
along the ridges this afternoon in lingering instability...but too
little of that for thunder. Stubborn low clouds/fog will break
into a cumulus deck for many areas by midday...with slow erosion from
the west with time as drier air works in. Minor tweaks to
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 /6 PM this evening 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/...
a deamplified...flattened upper flow is prognosticated by model
ensembles through the long term period. Individual shortwaves
advancing through the flow across the upper Ohio Valley are
expected to bring periodic chances for showers and thunderstorms.
Used wpc ensemble based guidance to smooth out model
differences...with some adjustments to probability of precipitation and the prognosticated
seasonally warm temperatures.
Aviation /14z Saturday through Wednesday/...
dry advection behind the exiting trough should allow for celings
to lift and eventually scatter out later this morning and early
afternoon with a return to VFR. MVFR to possible IFR is expected
again late tonight as fog forms with a moist ground.
Outlook.../Sunday through Wednesday/...
restriction chances are expected to increase early next week with
several crossing disturbances.