Area forecast discussion
National Weather Service Pittsburgh PA
702 PM EDT Wednesday may 22 2013
Synopsis...
shower and thunderstorm chances will continue until a cold front
passes through Thursday evening. High pressure returns for the
weekend.
&&
Near term /through Thursday/...
recent mesoscale data shows ml convective available potential energy average 500-1000 j/kg over WV into western
PA. Still possible for an isolated severe thunderstorm over the next hour or two
until instability fades. Another surge of moisture seen on satellite is experimental
to move northward keeping shower chances into the overnight period. Still a chance of a
thunderstorm with some elevated instability but severe threat should end. A cold front
will aprch from the west Thursday bringing addnl shwrs/tstms. Model forecasts
show instability should be minimal and this seems reasonable given expd
cloud cover.
&&
Short term /Thursday night through Saturday/...
a rapid transition to much colder conditions takes place during
this period as the consensus of the more reliable global model
systems suggesting the middle-level system tracking through the
region should close off as it moves over Pittsburgh and slowly
oozes southeastward. The closed solutions favored by the more
reliable models end up trending toward the slower end of the
guidance pack with this system...which makes sense given the
higher long wave amplitude. As such...the systems departure was
slowed in the forecast which resulted in increasing probability of precipitation into
Friday.
While its departure is slower...much drier air does work into the
area by Friday night with the consensus offering extremely lean
layer relative humidity profiles and weakening northwest cold advection. This
sets the stage for stellar radiational cooling going into Saturday
morning. Gridded guidance suggests widespread 30s across the
area...which with 850 mb temperatures falling toward -2c is not too
shocking. Frost was added to the grid to accommodate lows
generally in the middle 30s across vast tracts of the County Warning Area...and
frost/freeze headlines seem possible at this point. These
temperatures at 850 mb fail to moderate during the day Saturday
much...so temperatures will likely only wander for highs from the
upper 50s Friday toward the lower 60s Saturday. Fries
&&
Long term /Saturday night through Wednesday/...
similar conditions persist through the rest of the weekend and
even possibly into Monday morning with very dry conditions and
light winds favoring Superior radiational cooling each night. As
such...lows continue to look to head toward the 30s each
night...with a few locations inevitably dropping below freezing.
Once again...frost was added to the forecast into the
overnight/early mornings this weekend...and frost/freeze headlines
again seem quite possible.
Otherwise...very gradual moderation of low level temperatures will
be likely as the closed system departs eastward but dry cyclonic
northwesterly flow aloft remains the large controlling factor for
our weather. This is thanks in part to the fact that the model
consensus keeps the large scale ridge axis largely to our west
through the middle of next week. As a result...conditions should
remain generally dry with very slow moderation of temperatures
through the week. Fries
&&
Aviation /00z Thursday through Monday/...
thunderstorms beginning to decreases this evening...and this should continue. Should
still be scattered showers around into the overnight hours but genl VFR weather is
experimental. A brief period of MVFR ceilings is possible Thursday morning before VFR cumulus/stratocu
returns. A cold front will move across the region late Thursday bringing MVFR showers
near or just after the end of the taf period. A thunderstorm is possible but
probability looks low at this time.
Outlook.../Thursday night through Monday/...
restrns are likely in showers Thursday night after frontal passage. High pressure and VFR
conds expd Friday through Monday.
&&
Pbz watches/warnings/advisories...
Maryland...none.
Ohio...none.
PA...none.
WV...none.
&&
$$
07
