Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1026 PM EST Friday Mar 6 2015
high pressure will build southeast over the state tonight. A weak
area of low pressure will pass north of the region tonight and
Saturday. Overall the pattern favors moderating temperatures and
no significant storminess for the next several days.
Near term /until 6 am Saturday morning/...
late evening satellite loop shows upper level shortwave and associated batch
of cirrus beginning to shift east of the area at 03z. As this
feature passes east...expect clear skies for the balance of the
night across much of central PA. However...next shortwave over the
Great Lakes will spread clouds into the northwest mountains after midnight.
Main forecast challenge in the near term will be overnight min
temperatures. Position of surface ridge across southeast PA will favor that area for
the coldest temperatures relative to normal. Ideal rad cooling scenario
across the lower susq valley with clear sky/calm wind will result
in another night of record cold. Further west...mins likely to be
reached around midnight across the northwest mountains...just before clouds and
increasing SW breeze develop. Overall...it looks like widespread
lows between 5-10f. However...normally colder valleys across the
lower susq valley will dip blw zero. Kthv...although not
representative of the area...is already down to -4f at 03z and
should bottom out between 5-10 blw zero.
Short term /6 am Saturday morning through 6 PM Saturday/...
a weak clipper tracking across the Great Lakes will spread clouds
into the region during the day with a bit of light snow/flurries by
afternoon...mainly north of I-80. Highest /categorical/ probability of precipitation are placed
across the northwest mountains...where orographic lift from SW flow will play
a role in some light accums. Model blended quantitative precipitation forecast supports a coating to
an inch along portions of the New York border...with probably nothing
south of I-80.
Saturday will start a temperature moderating trend that will
continue into next week. Highs will top freezing over much of the
region...and reach the 30s virtually everywhere.
Long term /Saturday night through Friday/...
beneath fast west to northwesterly flow aloft...frontal waves
will move along the baroclinic zone over the Ohio Valley
separating cold air in the Great Lakes/New England...and milder
air over the Missouri/Tennessee Valley. At middle levels the models
feature minor timing and amplitude differences...which will likely
continue given fast flow with weak surface reflection. Generally
the spread is minimal. The most discernible northern stream 500 mb
shortwave energy and weak surface clipper type low dropping southeastward
into the Great Lakes should result in increasing snow showers from
later Sat through Sunday...but with systems being quite progressive
and moisture remaining quite limited with no Gulf inflow..water
equivalents will be on the light side. Model qpfs are generally in
decent agreement on this scenario..so stayed close to their
consensus solutions with water equivalents below 0.25 inch and
48hr snowfall amounts of around 1-2 inches over the northwest mountains
ending 00z Tuesday. Temperatures will trend gradually warmer but still
below normal through Monday.
The models and ensemble means are agreeable/consistent with the
main themes of the large scale pattern into middle of next week.
These include progressive northern stream flow along the US/Canadian
border...Southern Plains into Mexico mean trough and strong ridge east of
the Bahamas. Gefs and naefs show a broader version of this pattern
into the second half of next week with above normal heights from
the western Atlantic nwwd across much of the eastern/central Continental U.S. Into the
Canadian rockies. Temperatures should continue to trend to the
upside and reach near to slightly above normal levels into
midweek. One trend that will need to be monitored is with
shortwave energy ejecting northeastward from Southern Plains trough into
confluent flow/upper jet entrance region over the middle Atlantic on
Tuesday. A model consensus shows a northward shift in the precipitation field
with the European model (ecmwf) being the most bullish. Will the cold air on The
Retreat timing may be crucial for determining ptypes. Plenty of
time to resolve the differences this in the coming days.
Aviation /03z Saturday through Wednesday/...
VFR conditions will continue into Saturday at all terminals...with
the possible exception of Bradford/kbfd where an MVFR ceiling is
possible Saturday as a weak frontal system approaches the area.
Sat...mainly VFR. Possible restrictions north.
Sun-Mon...MVFR with chance -shsn mainly north and west. VFR southeast.
Tue-Wed...no sig weather.
the low temperature of 0 degrees this morning at Harrisburg is the
coldest minimum temperature on record for the month of March. The
previous coldest minimum temperature for March was 5 degrees set
in 1984 and 1900. The low temperature of 0 degrees also broke
the daily minimum temperature record. The previous daily record
low was 7 degrees set in 1901. A continuous weather record has
been kept at Harrisburg since 1888.
short term...Fitzgerald/la corte