Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
930 am EDT Sat Aug 30 2014
showers and thunderstorms will become more numerous later tonight and
Sunday with increasing humidity.
Near term /through tonight/...
low pressure is set to move from the upper Mississippi Valley into
the upper Great Lakes during the daytime today. An increasing
pressure gradient ahead of this is likely to increase southerly
flow over the area as the day wears on. Additionally...isallobaric
flow looks set to increase downslope flow off the ridges into the
afternoon hours. This will have a few ramifications for the
forecast. First...warm advection and increased flow mean increased
low level mixing going into the afternoon. This should allow
temperatures to make aggressive rises into the afternoon hours.
Second...downslope flow will both increase compressional warming
from Indiana through Marion counties...while also minimizing the
chance of surface-based instability showers through the afternoon.
As a result of these two things...probability of precipitation were centered in the ridges
and northwestern zones through the day today...with the central
corridor of the County Warning Area largely lowered below the threshold for
mentioning precipitation. Additionally...high temperature
expectations were nudged up a tad to account for a more well mixed
profile going into the afternoon. Fries
Short term /Sunday through Tuesday/...
likely probability of precipitation maintained into Sunday as shortwave moves across
region. As shortwave exist showers will decrease northwest to
southeast Sunday night. Monday will be warm and humid with only
scattered showers and storms in low level instability but no real
upper level support. By Tuesday fairly strong upper level trough
and cold front will approach with likely probability of precipitation especially by
afternoon. Continued warm and quite humid ahead of the front.
Long term /Tuesday night through Friday/...
showers and thunderstorms will linger Tuesday night as cold front
pushes east. High pressure moves over the East Coast Wednesday...and
should manage to deflect precipitation associated with a cold front
to the north until at least Friday. Cold front could get close
enough by Friday afternoon to bring at least an isolated shower to
western areas. Temperatures will be a few degrees above normal.
Aviation /14z Saturday through Wednesday/...
scattered cumulus is expected at all terminals this afternoon...and
cannot rule out some scattered convection west of duj and pit.
Chance for precipitation is too low to include in tafs at this time.
Southerly winds could present crosswind issues at some
airports...especially with the chance for 15-20 knots gusts to develop.
Widespread precipitation is expected with an approaching cold
front...but precipitation is not expected at terminals until at least 06z