Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1255 am EDT Sat Mar 28 2015
scattered snow showers and flurries will end as cold high pressure
builds in over the weekend.
Near term /until 6 am this morning/...
minor adjustments were made decreasing hourly temperatures
slightly to better align with latest surface observations. No
major changes were necessary as latest radar trends continue to
show snow shower activity diminishing across the forecast area.
Previous discussion follows..
Cold advection and shortwave support are prognosticated to keep
scattered snow showers and flurries across the region especially
early tonight...though little if any accumulation is expected.
With weakening lapse rates later tonight...a decrease in precipitation is
expected. Lows around 15 degrees below the seasonal average are
expected using modified lamp guidance.
Short term /6 am this morning through Monday/...
upper trough axis swings through the County Warning Area Saturday morning...quickly
followed by the 850 mb thermal trough. Any remaining snow showers
should end in the morning. Low clouds will break through the
day...and expect mostly clear skies by sunset. Much below normal
high temperatures are forecast...actually lowered the forecast a degree
or two in the afternoon.
Saturday night and Sunday will be dry as middle level ridge
approaches and passes along with a tranistory surface high. Said
high passes just to our south during the night. A good radiational
cooling setup is expected....with most low temperatures in the
teens. Not expecting widespread record lows at this point...
although readings will not be too far off. High clouds will begin
to arrive Sunday as they spill over the ridge axis. Low level flow
switches to west and southwest...bringing in a warmer airmass.
High temperatures still below normal but some 10-15 degrees warmer than
There is a bit better agreement between the NAM and the GFS
regarding the timing of the shortwave/frontal combination slated
to arrive Sunday night into Monday. Looks warm enough to keep any
mention of snow to the north of pit and along the ridges. Still
not impressed with quantitative precipitation forecast potential given system speed and will
continue with high chance probability of precipitation. A slow warming trend will continue
with Sunday night/Monday temperatures.
Long term /Monday night through Friday/...
the longwave pattern will become more zonal in the extended with
temperatures returning to near normal. Shortwave passages with
precipitation chances are currently anticipated for Tuesday and Thursday.
Aviation /06z Saturday through Wednesday/...
cold advection through the top of the boundary layer is expected to
maintain snow showers through the evening...and MVFR...to low VFR
stratocu through Saturday morning. Increasing subsidence and dry
advection over a still ice covered Lake Erie should alleviate
conditions as Saturday progresses.
Outlook.../Saturday night through Wednesday/...
the next chance for widespread restrictions is expected with a
Sunday night frontal system.