Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
1017 am EDT Friday Mar 27 2015
light precipitation and well below normal temperatures will
persist into tonight. Temperatures will be well below normal
through the weekend.
Near term /through tonight/...
upper level trough moving toward the region this afternoon with a
small area of snow showers on the increase ahead of it into
eastern Ohio and northwest PA. Have adjusted probability of precipitation to account for this but
not a major change. Cold northwest flow tonight as cold advection
continues. Snow showers across the I-80 corridor and into the
ridges may give a quick coating early before quickly diminishing
as subsidence works into region with surface high pressure. No
changes to forecast temperatures which will average 10 to 15 degrees
Short term /Saturday through Sunday/...
with the upper trough moving to central Pennsylvania by Saturday
morning...any lingering precipitation should quickly push east after
sunrise. Even with skies clearing Saturday...cold northwesterly
winds will keep highs from rising much above todays values. Winds
will diminish Saturday night as high pressure moves
overhead...allowing for full radiational cooling and yet another
night of lows in the teens. Return flow behind the high pressure
will finally bring some relief from colder temperatures...although
daytime values on Sunday will still remain 5-10 degrees below
normal. Next front crosses the region Sunday night...with models
still varying in exact timing and amount of deep moisture present.
GFS appears to be the fast outlier...and have gone closer to
NAM/sref timing. Raised probability of precipitation from previous forecast...but still do
not have confidence to add likely probability of precipitation anywhere. Sunday night should
finally bring a period of near normal temperatures...meaning that
precipitation should generally fall as rain. Flow differences
between the GFS/European model (ecmwf) result in some uncertainty as to whether
showers will linger into Monday. For now...have gone with chance
probability of precipitation diminishing through the day. Highs on Monday should continue to
creep up a couple more degrees.
Long term /Sunday night through Thursday/...
the longwave pattern will become more zonal in the extended with
temperatures returning to near normal and shortwaves Tuesday
afternoon through Tuesday night and again on Thursday bringing chances
of precipitation to the region.
Aviation /14z Friday through Tuesday/...
brief window of MVFR snow showers northern taf sites late morning
will give way to highly variable conditions this afternoon but
MVFR at worst. Cold advection strato-cumulus will continue with stray
snow showers at ports this evening. Building high pressure and
subsidence will bring improving conditions toward daybreak. Winds
will remain northwest 5 to 10 kts.
Outlook.../Saturday through Tuesday/...
VFR expected later Saturday early Monday morning as low pressure
impacts the region.