Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
245 PM EDT Monday may 25 2015
warmth and humidity have returned to the upper Ohio Valley region...but
shower and thunderstorm chances can be expected for most of the coming
Near term /through tonight/...
intensifying southwesterly flow will continue to advect warmth
and moisture over the upper Ohio region through tonight. Changes
to an already warm temperature forecast were not appreciable.
Adjustments to probability of precipitation included an upward bump for scattered...I.E. Chance
numbers across the western perimeter of the pbz County Warning
Area late this afternoon and this evening...as well as in the
predawn hours of Tuesday as NAM and GFS persist in progressing
another shortwave across the region. In general...these have been
weather labeled as scattered showers given the absence of instability
on various model soundings in response to increasing middle level
warmth. An exception was made for the Zanesville and New
Philadelphia corridor where warmth and increasing dewpoints may
just support enough instability for a sligth thunderstorm chance
early this evening.
Short term /Tuesday through Thursday night/...
continued southwest flow will maintain The Funnel of deep moisture
over the upper Ohio region...at least until the advancing middle level
trough axis progression shunts the plume eastward by Thursday as
per the GFS and NAM solutions.
Chance...to likely shower and thunderstorm will thus be maintained
for the period. The best overall probability of precipitation at moment are still prognosticated
for Wednesday...although todays model runs are faster in pushing
the parent middle/upper level trough axis and sustained moisture tap
eastward...so those likely numbers were trended slightly eastward
The short term severe potential still looks to be compromised by
warm middle levels and a marginal deep layer shear profile...but warm
rain processes and training may support locally heavy rainfall
until moisture and warm cloud depth wanes later on Wednesday.
No major changes were needed for the seasonably warm temperature prognosis.
Long term /Friday through Monday/...
precipitation chances will increase again for the weekend...and persist
into next week as models agree on a weak split flow regime
converging over the Great Lakes/upper Ohio region. The surface
front is projected to sag southward until redeveloping northward
as a warm front in response to Great Plains troughing early next
Given model magnitude...positioning...and timing disputes...persistence
will rule the long term forecast strategy.
Aviation /18z Monday through Saturday/...
generally VFR is expected to continue through tonight as the eroding upper
ridge over the region suppresses convection. However...isolated...to
scattered showers will increase local restriction potential and
moist southerly flow may spawn a stratus/stratocu layer early on
Tuesday. Tafs thus include a vicinity shower mention and a late
period...low end VFR cloud base forecast as a low confidence
Outlook.../Monday through Friday/...
abundant moisture and disturbances in southwest flow are likely
to spawn periodic restrictions through Wednesday.