Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
133 am EDT sun Aug 30 2015
isolated to scattered rain showers through Sunday as a weakening
area of low pressure approaches the upper Ohio Valley region.
Near term /through today/...
weakening upper-level shortwave trough currently located in
southwest Michigan is generating scattered showers and
thunderstorms through northern and central Ohio. Latest infrared
satellite imagery shows cooling cloud tops along a line through
Columbus and into our extreme western zones. This coincides well
with the southern edge of the higher precipitable water values
along with upper-level divergence from the right entrance region
of the 300mb jet streak. While instability and shear continue to
underwhelm...these modest features alone are enough to prolong the
shower/thunderstorm activity into the early morning hours.
Expecting showers to weaken through the pre-dawn hours as the
upper trough flattens and departs...and the aforementioned upper
level support moves out. After daybreak Sunday comes a bit of a
transition as the front washes out. Despite the presence of any
organized ascent...weak mesoscale impulses along the lingering
boundary could combine with moisture to produce disorganized
showers and thunderstorms Sunday afternoon. Will continue to carry
chance/scattered wording through the evening.
Short term /tonight through Tuesday/...
the shortwave is expected to continue its advancement across the
region Sunday and Sunday evening...as its associated surface
trough/weak cold front gradually dissipates. Continued with low
end probability of precipitation for showers as organized upper support is lacking. A few
afternoon storms are also possible with limited instability.
A weak upper trough axis mainly south of pit should keep slight
chances for showers or storms on Monday...though warming middle
levels should cap off the atmosphere by late in the day. This
capping...and weak ridging...should allow for mainly dry weather
on Tuesday. Temperatures should continue several degrees above
average using the latest GFS MOS and sref guidance.
Long term /Tuesday night through Saturday/...
h500 ridging pattern takes hold through the extended period...with
no organized weather systems foreseen through Saturday. Appears to
be just enough moisture for isolated diurnal convection into
Friday at least...and elected to add slight chance probability of precipitation each day.
However...the strength of middle level capping will need to be
evaluated as time GOES on to determine the daily precipitation
chances...with Friday and Saturday particularly noteworthy dry
candidates. More certain is the likelihood of continued above
normal temperatures...and HPC guidance was used in combination
with the previous forecast for the values.
Aviation /05z Sunday through Thursday/...
upper-level trough moving across region...resulting in showers and
thunderstorms blossoming over Ohio. However...much of this
activity will remain north of most terminals through
daybreak...except perhaps zzv and fkl. Otherwise...no restrictions
are expected as we flirt again with edge of the middle-level cloud
deck. Winds will be light mainly from the west. Continued general
VFR ceilings later today with only scattered showers at best with
weak upper support and shallow moisture.
Outlook...Sunday night through Thursday...
general VFR except for possible patchy morning fog the remainder of