Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
906 PM EDT Thursday Mar 26 2015
a deep upper level trough over the miss vall will swing east across
Pennsylvania this weekend...bringing cold weather. The upper
level flow becomes more zonal next week...so temperatures should
rebound toward normal.
Near term /until 6 am Friday morning/...
surface analysis at 01z shows cold front has cleared the southeast
counties...ending the threat of thunderstorms and rain. Across the Allegheny
plateau...residual low level moisture ascending the high terrain
will produce scattered -shra early...then scattered -shsn overnight. Light
quantitative precipitation forecast and marginal surface temperatures should limit accums to just a coating
Across the southeast counties...deepest moisture has exited the area.
However...near term model data continues to imply a good chance of
additional rain showers overnight...as weak wave of low pressure rides
up stalled frontal boundary just to the southeast of PA. Across the
Ridge/Valley region from kaoo NE through kipt...downsloping northwest flow
will likely limit additional precipitation overnight to a few
sprinkles/flurries at best.
Blend of 18z consall and latest lamp suggest temperatures by dawn will
range from the M/u20s over the northwest mountains...to around 40f across the
lower susq valley.
Short term /6 am Friday morning through 6 PM Friday/...
any early showers across the southeast counties should end by late
am...as secondary surface wave exits the middle Atlantic coast.
Elsewhere...approach of upper level trough could support a few PM
snow showers...mainly over the alleghenies.
Strong cold advection and 850 hpa temperatures forecast to fall well
below normal will result in an unseasonably cold day for late
March. Maximum temperatures should range from only around freezing over the northwest
mountains...to the m40s in lower Susquehanna valley. The coldest air at
850 hpa with -2 to -2.5 Standard deviation anomalies comes by
Friday evening into Saturday.
Long term /Friday night through Thursday/...
upper trough deepening over the eastern U.S. At the start of the
period will affect the weather through at least the early part of
the weekend. Significant precipitation associated with this trough
should have concluded by daytime Friday...but several shortwaves
rotating around the upper trough will slow the advance of the
otherwise progressive trough/associated surface low...causing lingering
showers into Saturday.
Area of high pressure should eventually move into the region for
Sunday into early next week.
Behind the deep upper trough will bring another shot unseasonably
cold air into the region...especially noticeable after a couple
days of more Spring like conds today. Temperatures will be 10 to
20 degrees below normal over the weekend.
A comparatively weaker northern stream wave will move across the upper
Great Lakes region and towards the northeast on Monday. This will
continue the chilly temperatures as well as bring the chance for more
snow showers. Weather will dry out but remain cool for the middle
of next week as another area of high pressure arrives behind
Aviation /01z Friday through Tuesday/...
key issue over the next 24 hours is the timing of the front and
the frontal rain and isolated thunderstorms. There will also be
some issues with rain to snow in northwestern PA this evening.
The best chance for modest thunderstorms is int the 20z to 00z
timeframe mainly in central and southeastern areas. There could be
a weak line of showers and thunderstorms in southeastern areas
The rain....snow....and line of showers will produce areas of MVFR
and IFR. Behind the frontal system moisture could produce some
areas of patchy fog and areas of snow showers in the
northwest...areas of IFR and MVFR.
The cold air comes in and could change the rain to snow over the
entire region by Friday. Mainly VFR and some areas MVFR in snow
showers in mountains.
Friday will be a mostly VFR areas MVFR in snsh. Windy day with
some gust spread issues.
Fri-Sat...MVFR/IFR with snow showers north/west. VFR to MVFR central
and east with schc of -shra.
Sun...no sig wx/VFR.
Monday...chance of light rain /light snow early/ across northwest half with
MVFR reductions. VFR southeast.