Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
922 am EDT Monday Mar 30 2015
after a cold front crosses the region this morning...low pressure
tracking across the region tonight into Tuesday will bring another
round of precipitation. A warming trend will continue through the
Near term /through Tuesday/...
the system from last night is quickly exiting stage right...with
substantially drier boundary layer air quickly infiltrating the
region in its wake. While this will lead to rapid improvement this
morning...northwesterly flow behind the system will also allow for
much colder middle-level air to advect toward the area by afternoon.
Rap 700 mb temperatures fall from around -10c to -16c through the
afternoon as this colder air arrives aloft...which means any
sunshine we see is likely to be destructive and allow for cumulus
development. Additionally...a lack of middle-level moisture erosion
combined with stronger lapse rates by afternoon may allow for some
isolated rain shower development across the northeastern reaches
of the County Warning Area. With cold advection ruling The Roost
today...temperatures will again remain below normal. Fries
The break from precipitation will be relatively short lived as low
pressure tracks right across the forecast area tonight into Tuesday.
General trend is that precipitation will move into the area slightly
earlier than previously forecast. That will allow precipitation to
start as snow along the Interstate 80 corridor...but all precipitation will
change over to snow by the afternoon. As much as an inch of snow
could fall in some locations. Have gone with likely probability of precipitation to the
north and east of Wheeling and Morgantown...but if the European model (ecmwf) model
is correct...might need to expand likely probability of precipitation farther to the south
and west. Tuesday will have a pretty wide spread of high
temperatures...ranging from the lower 40s in the north with
extensive cloud cover to the upper 50s in the south where a little
bit of sun is expected.
Short term /Tuesday night through Thursday/...
a lingering shower may persist in the southeast Tuesday
evening...but partial clearing is expected as high pressure moves
into the region. Once flow turns to the southwest Wednesday
afternoon...this should clear all cloud cover. With winds out of the
northwest most of the day...there will be little change in
temperatures Wednesday compared to Tuesday. Attention will then turn
to low pressure tracking across Canada dragging a cold front across
the United States. Models have been back and forth on timing of this
system for the last couple of days...and there is still little model
consensus at this point. For now have gone with chance probability of precipitation during
the daytime. Regardless of timing...strong southwesterly flow should
allow for a much warmer day...with most locations from Pittsburgh to
the south warming into the 70s.
Long term /Thursday night through Sunday/...
decent precipitation chances will continue into the weekend as the
front sags across the region and provides focus for subsequent low
pressure passage later on Friday...with an eastward exit on
Saturday. This forecast was based on a blend of GFS trends and wpc
guidance with shortwave timing and boundary placement likely to
remain questionable for a few days.
The Thursday warmth will thus be short lived...but the cooldown
will not be as dramatic as this past weekend given the zonal flow
that is prognosticated aloft. Tweaked wpc guidance was used for the
seasonably cool temperature forecast.
Aviation /13z Monday through Friday/...
light showers of rain and snow with MVFR ceilings will accompany
a cold front across the region early this morning. Surface gusts
of 20 to 25 knots can be expected with a wind veer to the west.
Condition improvement is anticipated after daybreak as subsidence
and dry advection increase.
Outlook.../Tuesday through Friday/...
restrictions are likely with crossing low pressure on Tuesday and
again late Thursday and Friday.