Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1117 am EDT Sat Aug 29 2015
after a warm and dry Saturday...rain chances return late tonight
and Sunday with passage of a weak cold front.
Near term /through tonight/...
high pressure centered over eastern PA is expected to bring dry
and warm weather today. Clouds are expected to increase by evening
with the approach of a weak shortwave. This wave will also bring
slight chances for showers and storms as it approaches. The pbz
morning sounding supports highs a little above seasonal levels
today...with lows around 5 degrees above average tonight.
Short term /Sunday through Tuesday/...
front will settle into the forecast area on Sunday. However...with
midlevel support weakening and pulling off to the east...and surface
high pressure in control...the front will stretch out and largely
dissipate. Enough moisture and instability will remain for
scattered showers and storms. Coverage will be influenced by
diurnal factors...with a peak during the afternoon hours. Going to
keep probability of precipitation in the chance range due to lack of large-scale
forcing...with values dropping to slight chance Sunday night. Precipitation
totals will likely remain under a quarter inch in general...and will
not do much to alleviate the overall dry antecedent conditions.
On Monday...a drier and more stable airmass will try to sink into
the County Warning Area...but will be hindered by weak midlevel energy moving
northwards across the central Appalachians. Do not think that this
fairly diffuse vorticity will make it to the Pittsburgh area...but
there will be enough support for some isolated rain showers/thunderstorms and rain mainly
south of I-80. So will maintain a slight chance pop during the day.
Loss of heating plus stretching/weakening of vorticity energy will allow
precipitation to cease by sunset. Drier air makes a little more
headway south on Tuesday...and think isolated diurnal convection
will be limited to south of pit.
Blended mosguide with going forecast to derive temperatures. Not
much change to values...with above normal temperatures throughout.
Long term /Tuesday night through Friday/...
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 /15z Saturday through Wednesday/...
a weak front will approach this afternoon with a west to east
increase in middle clouds toward 00z. Only isolated light showers
expected as front dissipates across region later tonight...not
enough for any mention at any port. Winds will be light mainly
from the west.
Outlook...Sunday through Wednesday...
brief restrictions possible in scattered showers Sunday. General
VFR except for possible patchy morning fog the remainder of the