Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1138 PM EST Thursday Mar 5 2015
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
Near term /until 6 am Friday morning/...
as of 03z...skies have cleared across most of central PA as
Arctic high pressure system overspreads the state. Back edge of middle
level cloud deck should clear Lancaster Colorado by 05z...and patch of
stratocu over Warren/McKean cos should diminish by 06z...as
inversion heights fall.
Diminishing wind...clearing skies and fresh snow cover should
result in near record low temperatures overnight...averaging 5-10
blw zero over the northwest mountains...to the lower single digits across the
lower susq valley. However...a calm wind across the alleghenies
should allow the normally colder valleys to get even colder.
Latest rap suggests a few locations across the northwest could dip as low
as 15 blw zero. At this point...we are counting on the wind to
drop off enough to minimize wind chills...so no headlines are
planned at this time.
Short term /6 am Friday morning through 6 PM Friday/...
high pressure will provide a much brighter day Friday. Forecast
soundings suggest the potential for some stratocu to gather under
the strong subsidence inversion across the Allegheny plateau...but
even there a fair amount of sunshine should manage to mix with
any clouds that form.
Maximum temperatures should range from 20-25f blw normal Friday. 18z gefs
mean 925mb temperatures around -14c are supportive of highs from just the
upper teens over the Allegheny plateau...to the l-m20s across the
Long term /Friday night through Thursday/...
surface high pressure ridge axis will migrate eastward across the middle
Atlantic region Friday night and settle into the southeast states
on Saturday. An increase in SW gradient winds and clouds are
expected across the northwest half of the County Warning Area in advance of a weak low
moving across the Great Lakes. Meanwhile mainly clear skies and
lighter winds across the lower susq valley should prevail near
the departing surface ridge. This pattern favors a non-diurnal trend
with lows in the middle teens occurring early across the northwest mountains
Friday night with a steady to slow rise into Saturday morning. A
more typical nocturnal temperature curve should allow temperatures to fall to
around 10f over the lower sqv.
Broad upper cyclonic flow will continue into early next week as
additional shortwave impulses move from central Canada through the
northern tier of the U.S. There are fewer differences noted
overall compared to previous model cycles with respect to the
timing and depth of each impulse. One impulse will drive a surface
wave and associated front through the Great Lakes region on Sat
and then into New England on sun. An additional impulse will
take a similar track through the Great Lakes later sun into early
Monday along with a weak front. Given the fast deeper layer west
northwest flow over the region...the amplitude of each impulse
should be rather small with moisture availability quite limited.
Therefore expect occasional snow showers mainly over the higher
terrain of the northern alleghenies with 48 accums of 1-2"
possible over the northwest mountains by 12z Monday.
The models and ensemble means are agreeable/consistent with the
main themes of the large scale pattern into next week. These
include an increasingly zonal/progressive northern stream flow across
southern Canada...and southern rockies/plains into Mexico mean trough and
strong ridge east of the Bahamas. As the mean pattern aloft becomes
increasingly flatter...confidence is relatively high in a mainly
dry period with steadily increasing/moderating temperatures to at
or slightly above early-middle March climate normals.
Aviation /06z Friday through Tuesday/...
high pressure building into central PA at this time...with
pressure gradient keeping winds in the 5-10 miles per hour range early on.
These will lighten as the overnight progresses. VFR conditions
will be the rule...except in kbfd where a small stratocu deck will
bring MVFR conditions through about 06z before conditions improve
back to VFR.
VFR prevails on Friday under high pressure. Winds turn to the
southwest at speeds of 5-10 miles per hour.
Sun-Mon...MVFR with chance -shsn mainly north and west. VFR southeast.
Tuesday...no sig weather.
daily record lows are in serious jeopardy tonight at many
locations. The record low for March 6th at Harrisburg is 7f set
back in 1901 and -1f at Williamsport set in 1978.
short term...Fitzgerald/la corte