Area forecast discussion
National Weather Service Pittsburgh PA
117 PM EDT Wednesday may 22 2013
Synopsis...
upper level impulses brings an increase in showers and
thunderstorms through Thursday night...until a cold front crosses. Much
cooler weather is forecast this Holiday weekend under high
pressure.
&&
Near term /through Thursday/...
daytime heating continues to push our temperatures close to the
convective threshold. 16z mesoanalysis illustrates no cinh left
and equiv potential temperatures building. Still a fair amount of uncertainty
with the development of storms and how strong storms will be
later today and tonight. Latest thinking is storms will develop
along the Theta-E ridge axis which is building across WV and western
PA. Terrain induced storms are already underway over the central
mountains of WV. Farther west across Ohio...not sure how much development
will occur this afternoon until short wave trough passes around 0z.
Likely probability of precipitation still are on track for this evening for the entire
area. If the latest hrrr is correct we could see some localized
high water potential over northern WV with training of storms.
After midnight things should quiet down as llvls stabilize and we
await main trough axis to traverse from the west. NAM and GFS agree
on a period of dry or isolated activity tmrw from late morning through
middle afternoon before upper level impulses cross. Do not foresee a
severe weather threat Thursday due to lack of heating as an
abundance of clouds will be presence keeping thermodynamics low.
Greatest challenge is if NAM scenario of a batch of thunderstorms riding
NE from WV into southwestern PA around daybreak materializes. For
now...held off in favor of continuity per low confidence on this
outcome.
&&
Short term /Thursday night through Friday/...
a reinforcing front is prognosticated for Friday with residual shower chances
fading by afternoon with passage of that feature. As northwest flow develops with
passage of the aforementioned phased trough axis...cold advection will
limit temperature recovery. Expect highs about 10 degrees below the
seasonal averages undr the resulting high amplitude...eastern Continental U.S.
Trough portion.
&&
Long term /Friday night through Tuesday/...
the models are in good agreement on the overall upper level pattern
through the extended with an upper level ridging of the central
Continental U.S. And troughing in both the west and east. While this would
generally lead to a much less than confident forecast in the
shortwaves within the flow...this doesn't seem to be the case as
both the GFS and European model (ecmwf) suggest that much of the precipitation will
be suppressed south of the region through much of the period.
Thus...opted to take a blend of the models and HPC
guidance. Also...hedged a bit cooler with temperatures with
northwest flow present especially for the first half of the
period. This kept temperatures below seasonal averages Sat/sun
before moderating closer to normal for the rest of the period.
&&
Aviation /18z Wednesday through Monday/...
low to medium confidence forecast on shower and thunderstorm timing.
VFR weather will prevail much of the forecast period /at least into
the overnight hours/...the challenge is timing on any rain showers or thunderstorms and rain
impacting the terminals. Maintained thunderstorms in the vicinity for late afternoon and
evening before transitioning to VFR rain showers until midnight. Clouds
will develop in the predawn hours...latest guidance suggest ceilings
in the 015-025 which is higher than earlier runs and in line with
ongoing forecast. Stratocu will lift by middle morning into a low end
VFR deck. For places that experience rainfall...patchy fog could
develop during the predawn hours.
Outlook.../Thursday through Sunday/...
the probability of widespread IFR weather is low.
&&
Pbz watches/warnings/advisories...
Maryland...none.
Ohio...none.
PA...none.
WV...none.
&&
$$
Synopsis...98
near term...98
short term...15
aviation...98
