Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
707 am EDT Sat Apr 25 2015
rain chances will be on the increase today...especially over
areas from Pittsburgh southward as low pressure moves out of the
Midwest. Any snow showers rarly this morning will quickly end.
Near term /until 6 PM this evening/...
another quick update to bump up probability of precipitation in band of snow showers from
north of kphd to kpit and klbe. 0.3 snow measured here at the
office as band went by...with a coating reported elsewhere.
A pre dawn update was issued to add a snow mention for areas north
of the Turnpike as upstream observation are reporting precipitation beginning as
snow. A rapid change to rain is anticipated and overall low probability of precipitation
were maintained as per a lack of measurable expectations.
Warm...moist advection that is underway in advance of midwestern
low pressure is spawning middle level cloudiness and light showers
Precipitation is still expected to spread northeastward today...but
the projected track of the low should limit favorable isentropic
lift and deformation to southern counties of the County Warning
Area. Categorical to likely pop numbers were thus focused to the
south of Interstate 76 as per persistence and the more pessimistic GFS
Short term /6 PM this evening through Tuesday/...
the system is still prognosticated to move rapidly over the Atlantic on
Sunday...with a quick end to precipitation on Saturday night and early
Sunday is thus expected to be a day of improvement as surface high
pressure builds under northerly flow aloft. A fairly strong...but
moisture deficient shortwave is forecast to pass through the
western flank of upper low pressure early on Monday...slight to
chance probability of precipitation numbers were maintained mainly over the eastern half
of the County warning for passage of this feature...which may
include some snow showers or flurries.
Building surface high pressure under northerly flow aloft will
result in a dry...but cool Tuesday.
Temperature throughout the entire period were forecast using a
blend of NAM and GFS MOS...which was 5 to 10 degrees below the
Long term /Tuesday night through Friday/...
eastern Continental U.S. Upper troughing is expected to persist through the
week...so cool weather will persist. The best chance for
additional precipitation...albeit small...is projected for Thursday given
projections of a southern stream low phasing into that trough. Wpc
guidance captures the trend of the pattern sufficiently...hence
only minor alterations to that forecast were needed.
Aviation /11z Saturday through Wednesday/...
VFR conditions are expected through early this afternoon as high
pressure slowly exits. Middle level clouds will overspread the area
early this morning in warm advection ahead of approaching low
pressure. The low is expected to bring showers mainly south of pit
by middle to late afternoon...with eventual MVFR conditions with the
Outlook.../tonight through Wednesday/...
restrictions are likely to coninue south of pit tonight with the
low pressure. Restricitions are possible Monday with an upper