Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
841 am EDT sun may 24 2015
warmth and humidity will return to the region...but so will shower
and thunderstorm chances as the Holiday weekend draws to a close.
Near term /through tonight/...
dry weather will continue for the near term period as upper high
pressure builds over the upper Ohio and Great Lakes regions. A
gradual increase in humidity can also be expected as southerly
flow resumes with the eastward shifting surface high.
The intensifying warm advection regime will support temperatures
approximately 5 degrees above the averages.
Short term /Monday through Wednesday/...
recurring shortwave impulses are forecast to erode the ridge over
the region through middle week with moisture depth increasing in the
developing warm southwest flow. Shower and thunderstorm probabilities
will thus be on the increase beginning along a Zanesville to
Franklin line late on Monday.
As for severe potential...NAM and GFS deep layer shear projections
are marginal...with middle level warmth initially limiting explosive
instability. That same warmth would support heavy rainfall via
warm cloud processes...and precipital water values will be
appreciably higher under this train support pattern...but
convection potential is expected to be diurnally dependant and
sustained moisture convergence absent until a cold front slides
out of the Midwest on Wednesday.
The bottom line is that a hazardous weather outlook is not needed
at this time...although precursor rainfall and timing of an approaching
middle level trough may alter that diagnosis as middle week approaches.
Long term /Wednesday night through Saturday/...
the latest model runs agree on scenario of eastern Continental U.S. Ridge
erosion...with a weak cold front encroaching on the upper Ohio
region on Thursday. Chance probability of precipitation were maintained with that
timing...but eliminated for Friday given expectations of shortwave
ridging. A deeper shortwave trough with a stronger cold front
accompanied by increasing precipitation chances are projected for the
weekend. Temperatures are expected to average around the normals
for the period.
Aviation /12z Sunday through Thursday/...
high pressure will support VFR with light southerly wind into
Outlook.../Sunday through Thursday/...
abundant moisture and disturbances in southwest flow are likely
to spawn periodic restrictions through Thursday.