Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Pittsburgh PA
700 PM EST Sat Dec 27 2014
a cold front will be accompanied by showers tonight and Sunday
morning. A return to normal and below-normal temperatures will
Near term /through Sunday night/...
trends as expected in previous discussion continue on schedule. No changes made
in near-term. Previous discussion follows...
Showers are developing in southwestern Ohio at this time and will increase in covering early this
evening ahead of surging cold front. These showers will impact all of forecast
area overnight...so probability of precipitation were increased to match current MOS numbers as
precipitation is expected.
Cold front expected to cross forecast area late tonight and early Sun morning...
which will provide a rapid end from north to S as dry air invades.
Focus by afternoon will be far southeastern zones...where terrain may sustain
showers late in the day.
It appears that only limited cold air will arrive while precipitation is
ongoing...so a brief period of rain/snow will be possible at back end of
precipitation and in the rdgs sun aftn/eve. Very limited accums possible in the
rdgs...as warm ground elsewhere will be slow to feel the effects
of cold air arrival.
Maxima on sun likely will occur early in the day as cold air
arrives and clouds/precipitation suppress insolation much of the day. Minima
tonight will remain elevated for the same reason...but will drop into
the middle 20s-lower 30s Sun night amid cold air advection.
Short term /Monday through Monday night/...
surface hipres in the northern plains will ridge eastward into the Great Lakes region Monday-
Monday night. Light northwesterly-northerly low-level winds will persist beneath Stout
middle-level flow. Dry air should preclude precipitation most zones this period...
but a developing coastal low may spread light precipitation westward into rdgs Monday
Long term /Tuesday through Saturday/...
the extended will largely be dry with a decreasing trend in
temperatures as a broad trough in the longwave pattern slowly sags
south across the eastern Continental U.S..
Potent shortwave trough expected to impact forecast area Friday night and Sat. Both
GFS and European model (ecmwf) show temporal consistency...although the exact
track of the system differs. Regardless...the surface feature passes
to the northwest of the forecast area...leading to strong warm air advection
that should keep precipitation liquid. Only caveat will be sub-freezing
temperatures at onset...which could spell a freezing rain scenario for areas
that typically retain cold air...especially sheltered vllys in ridge
counties and northern zones. Probability of precipitation were increased day 7 given expected measurable
precipitation...but uncertainty remains in precipitation type.
Aviation /00z Sunday through Thursday/...
rapid deteriotation to MVFR should occur this evening as lowering
ceilings move in ahead of an incoming front. Shield of showers should
move across the entire area by 06z...with all areas falling deep
into MVFR or near IFR conditions. Beyond 06z...most areas will
likely go IFR with ceilings likely to remain IFR through Sunday
morning before MVFR conditions return by afternoon. Fries
Outlook.../Saturday night through Wednesday/...
periodic MVFR restrictions can be expected for the first half of