Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
304 PM EST Wednesday Mar 4 2015
a wave of low pressure will track south of Pennsylvania this
evening and early Thursday. High pressure will build southeast
into the state Friday and Saturday. A strong upper-level ridge
will build into the region early next week. This should provide
generally fair weather and several days of near normal
temperatures and relatively dry weather.
Near term /until 6 am Thursday morning/...
2 PM update:
After ingesting new 12z data and latest ensembles...it is becoming
apparent that the axis of heaviest precipitation will tend to be a bit
further south than previously anticipated. We have trimmed back
the warning to our southern border counties...and lowered the
overall numbers more in line latest quantitative precipitation forecast/westward snowfall guidance.
Still possible the warning configuration is a bit too robust and
may yet need further trimming later this evening as we gather
newer ensembles and hrrr data.
Temperatures have recovered above freezing over all but the far
north. Temperatures for much of today will remain steady or slowly rise
before colder air begins working in later today and tonight.
Colder air arriving later today and this evening will bring a
change back to snow. Latest BUFKIT soundings show snow in
Johnstown by 20-22z...Altoona/State College 22-00z...and not until
03-6z in the Harrisburg-York-Lancaster areas. It's over these
southeastern zones where the problem will be as much of the precipitation
that is expected will fall as rain before the cold air finally
A strong jet entrance region aloft will slide by just north of
the region tonight and Thursday...supporting an area of potent
low-middle level frontogenetic forcing. Models respond by bringing a
fairly prolonged period of precipitation to my far southern zones.
Sref and gefs threat pages still paint my far southeastern zones as
having the highest risk for heavy snow through middle day
Thursday...with a rather sharp cut off on the back side up into
the central mountains.
Short term /6 am Thursday morning through 6 PM Thursday/...
latest gefs/sref show precipitation ending from northwest to southeast as the day
wears on with much of the day ending up dry over my northern
tier...and mainly dry after 18z north of I-80.
Still yet another very cold day is in store with maximum temperatures some
20-30 degree below normal.
Long term /Thursday night through Wednesday/...
High pressure and below normal low-level temperatures will
dominate the region Thursday night into late Friday. Unseasonably
cold air...perhaps the last of the significant Arctic surges of
our endless winter.
Based on the low temperatures near and below 0f and the
winds...the potential exists for some areas to experience wind
chills overnight Thursday into Friday which might require an
advisory across the northern tier counties.
Saturday the temperatures at 850 mb return closer to normal and
high pressure drifts to our south. Pennsylvania should remain
north of this weak high....cutting off any moisture to the
south...keeping the region in weak westerly flow into Monday. The
period should be relatively dry with any frontal precipitation
suppressed to our south and only weak northern stream waves to our
north to generate any precipitation.
So...kept the probability of precipitation low through the period and any light
precipitation would likely be snow as 850 hpa temperatures stay below 0c.
Best chance of any precipitation would be in northern areas should
one of the northern stream waves prove to be stronger than
A ridge is forecast to build over the region Tuesday into
Wednesday and our lower troposphere temperatures should get at
least slightly....above normal....both Tuesday into Wednesday.
This should provide at least 2 days of near seasonal temperatures
for a change. Relatively warm days and cold nights...a good slow
way to melt snow without flooding.
The naefsbc and gefsbc suggest a frontal passage Thursday with
slightly colder temperatures as another high pressure system is
forecast to move over the northeastern United States Thursday into
Saturday next week.
Aviation /20z Wednesday through Monday/...
a wavy cold front to the south of the area will bring another
round of rain/snow mainly to areas south of I-80 tonight into
Widespread MVFR/IFR will continue overnight through at least middle
day Thursday before dryer air begins moving into the region from
the west and north bringing improving conditions.
Thursday...slowly improving conditions...lingering MVFR northwest and southeast.
Sun-Mon...MVFR with chance -shsn mainly north and west. VFR southeast.
Flood Watch until 7 PM EST this evening for paz017-024-025-033-
Winter Weather Advisory from 7 PM this evening to 7 PM EST
Thursday for paz017>019-024>028-049>053-058.
Winter Storm Warning from 7 PM this evening to 7 PM EST
Thursday for paz033>036-056-057-059-063>066.
near term...la corte
short term...la corte