Area forecast discussion
National Weather Service Pittsburgh PA
643 am EDT Wednesday may 22 2013
Synopsis...
thunderstorm chances will increase today as a cold front
approaches the region.
&&
Near term /through tonight/...
low pressure which has plagued the plains is still forecast to develop
northeastward and phase with eastern Canadian trough by Thursday. Tail of
coupling jet aloft is expected to apprch the upper Ohio this evening and
cross the region tonight while surface low is projected to move rapidly
northeastward across Lake Erie.
With relatively moist airmass already in place...Post daybreak
destabilization and eastward sliding middle/upper trough will likely spprt thunderstorm
development by afternoon and into the evening.
Given the strengthening wind field as mentioned above...concur
with the Storm Prediction Center assessment of severe potential as
evening apprches. Risk will remain in the slight category...I.E. Approx
30 percent chance of the primary threat...which is of damaging wind
via short bowing segments.
Near term probability of precipitation were structured collaboratively for the most
part...with categorical numbers limited to Ohio and parts of northwest PA
immediately alng the Ohio border. Current thinking is that these
areas will have the better chance of widespread thunderstorm coverage
as potential mesoscale convective system progresses coincident with the low level jet...before
surface low lifts northeastward and diurnal warmth/surface based instability begin to
diminish after nightfall.
&&
Short term /Thursday through Friday/...
colder air is projected to advect over the region on Thursday as
surface front progresses eastward. However... with the middle-levels cooling
as well...convective thresholds will lower considerably with showers
and thunderstorms again becoming likely as the day progresses.
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 /12z Wednesday through Sunday/...
15-20 knots gusts can be expected to develop by noon at most
terminals along with diurnal cumulus. Showers and thunderstorms
are expected to develop by middle afternoon...and have continued thunderstorms in the vicinity
mention at this time. If anything...wind gusts may be
underestimated with possibility for thunderstorms and rain. The best chance for
restrictions and wind issues will come this evening as thunderstorm
coverage widens in a strengthening wind profile.
Outlook.../Thursday through Sunday/...
occasional restrns are likely into Thursday night with showers/thunderstorms as a cold front
moves across the region. An upper level disturbance will bring possible restrns
in rain showers Friday before high pressure and VFR conds return Friday night through
sun.
&&
Pbz watches/warnings/advisories...
Maryland...none.
Ohio...none.
PA...none.
WV...none.
&&
$$
