Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
153 am EDT sun Aug 30 2015
increasing moisture will be channeled northeast from the Ohio
Valley today...and interact with a stationary frontal boundary to
produce scattered showers and a few thunderstorms across mainly
the northwestern half of the state. High pressure off the middle
Atlantic coast will be more influential on keeping fair and dry
weather intact across the southeastern half of Pennsylvania.
Very warm and increasingly humid weather will continue into the
middle of the upcoming week.
Near term /until 8 am this morning/...
stable stratification under clear to partly cloudy skies will
continue across much of central and southern Penn through the middle
morning hours. Over northwestern Penn.
Surface based cape will slowly increase to between 300-500 j/kg
across the northwest mountains this morning with the advection of 1.5 inch
precipitable water air from the Ohio Valley. The presence of a quasi-stationary
frontal boundary and the increasing moisture from the Ohio
Valley...will lead to newrd expansion of showers and a few
isolated thunderstorms and rain early today.
Patchy light River Valley fog expected elsewhere as surface dewpoints
Min temperatures should range from the middle to upper 50s over the north...
to the lower 60s in the southeast.
Short term /8 am this morning through 6 PM Monday/...
some early morning fog in the valleys - which should be of lesser
coverage than Sat morning. Then...the temperatures rise even
better...adding another 3-4f onto Sat/S maxes.
Ridge at the surface and aloft is starting to get pressed a little to
the east by an advancing upper trough and slight feed of Gulf
moisture. Thus...support in the form of instability and moisture
will be available today.
Plan to increase probability of precipitation into the likely category across the northwest mountains
during the middle to late morning hours. There will be a transition
to virtually no chance of rain over the southeast counties of our County Warning Area.
Convective allowing hrrr model suggest even categorical are
warranted across parts of the northwest and ncent mountains /and even for a
more brief time period of a few hours over the Laurel Highlands
centered on daybreak/. This second...and more significant cluster
of convection will impact the northwest mountains of Penn between 10-14z.Some
locations will see between 0.25 and 0.50 inch of rain...where two
or more MDT-heavy showers occur.
After the initial...rather compact shortwave aloft lifts into
southcentral New York later this morning...the atmos will recharge
to over 1000 j/kg cape in some areas...and be capable of firing
off scattered rain showers/thunderstorms and rain across the central mountains...and alleghenies this
Highs this afternoon will vary from the u70s across the northern and
western mountains...to the upper 80s across the lower susq valley and
Long term /Monday night through Saturday/...
anomalous upper level ridge will dominate the Ohio Valley and
eastern United States much of the upcoming week...with 850hpa
temperatures running 16-18c which will translate to well above-normal
surface temperatures. This warmth and increasing humidity should allow for
at least a slight chance for diurnal convection each day...but the
probability of widespread rainfall is low.
There are a couple of interesting features that bear watching for
late in the long term period. The first is the remnants of
Erika...which are forecast to be in the vicinity of the Florida/Georgia coast by
the middle of next week. As this moisture diffuses over the
southeast u... of it will gradually crawl into the middle
Atlantic region. The other interesting feature is a backdoor cold
front that some models bring into the Middle-Atlantic States next
thurs/Fri. These features combined with the warm and increasingly
humid air that will already be in place will keep mention of at
least a slight chance for diurnal convection each day. The latter
feature could have an impact on temperatures late next week...tapering
back temperatures a bit.
Aviation /06z Sunday through Thursday/...
some weak showers will move across northwestern PA between 03 and
06z. Thunderstorms in the vicinity in kbfd. Otherwise patchy areas of fog mainly MVFR some
isolated are IFR. Models shows could be some isolated showers
before sunrise in far west.
Most models show highest chance of shower across northern
Pennsylvania Sunday in the morning. By 16z showers move into
Southwest Mountains. Used mainly vcsh/thunderstorms in the vicinity to handle showers as
the probabilities are generally 20 to 40 percent. Highest
probabilities of showers/thunder in northwest. Kbfd will likely
see a shower Sunday.
Monday...still some rain showers/thunderstorms and rain poss.
Tue-Thu...no sig weather expected areas MVFR overnight patchy fog.