Scientific Forecaster Discussion
fxus61 kctp 221054
Area forecast discussion
National Weather Service State College PA
654 am EDT Sat Jul 22 2017
a quasi-stationary frontal boundary will remain in the vicinity
of Pennsylvania through Monday. High pressure will build
southeast into the region for the middle of next week.
Near term /until 6 PM this evening/...
main focus in the near term is mesoscale convective system approaching from Ohio. Expect
convection to weaken later this morning as it moves into PA,
where CAPES are much lower. In addition, model soundings
indicate low clouds will be slow to mix out over the Laurel
Highlands, which will hinder diurnal heating ahead of mesoscale convective system and
reduce the severe threat.
Expect a progressively greater threat further east, where model
soundings and upstream satellite trends suggest there will be a
period of partly sunny skies filtered through some cirrus. The
resulting heating/destabilization could allow convection to
re-intensify along outflow of remnant mesoscale convective system over the south
central mountains and lower susq valley this afternoon. Latest
cams, including hrrr/WRF-arw/ncar ensemble, all time remnant mesoscale convective system
into the Laurel Highlands around noon, then the susq valley by
mid afternoon. Model downdraft CAPES do look favorable for
damaging wind gusts across the lower susq valley, if convection
Not much of a severe weather threat over northern PA today,
where very little cape is progged north of quasi-stationary
boundary. Mainly cloudy skies and showers across the north
should cap temps to the upper 70s and low 80s over the northern
mountains, while partly sunny skies push readings to near 90f
across the lower susq valley.
Brightening skies in wake of mesoscale convective system later this afternoon could set
the stage for another round of showers/storms this evening.
A quick check of ffg numbers indicates some pockets of wetter
ground across central PA, which could be susceptible to flooding
today. Ncar ensemble indicates the possibility of localized
amounts in excess of 3 inches possible across the central and
south central mountains by this evening.
Short term /6 PM this evening through 6 PM Sunday/...
a second round of strong to severe convection is possible across
the southern half of the forecast area this evening, as strong
low level jet and plume of anomalous pwats works through the
area. Bulk of model data then indicates a dwindling chance of
showers/storms from north to south overnight.
Favorable scenario for additional severe weather across central
PA Sunday afternoon, as the region will be within warm sector
south of anomalous surface low tracking eastward along the PA/New York
border. Moderate convective available potential energy and moderate westerly flow aloft,
combined with large scale forcing ahead of approaching upper
trough, should support widespread convection by afternoon.
Long term /Sunday night through Friday/...
some uncertainty continues with regards to timing of upper
trough passage early next week, but additional showers/storms
appear likely Monday, especially over northern PA. A period of
dry and cooler weather appears very likely by midweek, as upper
trough axis finally passes east of PA and surface high builds
into the area.
Aviation /12z Saturday through Wednesday/...
IFR cloud deck over far western porton of County Warning Area encompassing duj-
jst along with some valley fog across the north mountains early
this morning, but arrival of cirrus shield will slow expansion
of fog heading toward sunrise. Patchy fog restrictions will
develop over the lower susq, though most locales there will
After sunrise, fog in the southeast half will burn off between 12-13z,
and in the northwest under the cirrus deck will take into the mid
morning to return to VFR. Then attention turns to an approaching
warm frontal boundary which will be the catalyst for shower and
thunderstorm development around midday in the west spreading
eastward in the afternoon. Thunderstorm activity will be most
numerous south of I-80 with intermittent restrictions expected
into early evening
Thunderstorm coverage will diminish but convection will linger
over the southeast into the overnight. In addition, restrictions will
develop over northwest half of area.
Another round of convection driven by an upper trough will
begin to move into western areas around sunrise sun, which will
spread across central PA during the day bringing another period
of intermittent restrictions.
Sun...am restrictions likely northwest half. Thunderstorms and rain/rain showers likely with
Sun night...cig restrictions likely. Scattered tsra/shra.
Mon...am restrictions likely. Scattered thunderstorms and rain.
Tue-Wed...patchy am fog. Otherwise no sig wx.