Scientific Forecaster Discussion
fxus61 kctp 230034
Area forecast discussion
National Weather Service State College PA
834 PM EDT Thu Aug 22 2019
a cold front will push through the state this evening, bringing
fairly widespread showers and scattered thunderstorms to
southern Pennsylvania. Cooler and much less humid air will move
in for Friday and will last through the weekend.
Near term /until 6 am Friday morning/...
surface cold front extends nearly east/west along the i70-/76
corridor at 0030z, but will slow it southward progress for
several hours or more tonight as a weak wave of low pressure
slides east along it, beneath the right entrance region of a 115
knots upper jet axis located over SW Ontario.
Mesoscale-b scale area of mdtly strong uvvel aided by this feature,
and the presence of a 925-850 mb Theta-E ridge across scent PA,
will support another few compact areas of moderate to briefly
heavy rain sliding east across southern PA through about 07-08z
Expect another 0.25 to 0.50 inch of rain during the overnight
hours across the southern 1-2 layers of counties, while any
showers about 10 nm to the north of a kidi to kmui line will be
light and scattered, amounting to less than 0.10 of an inch
with little or no additional rain occurring to the north of the
Interstate 80 corridor.
Northern edge of the light to MDT rain will be near a khgr to
kthv and klns line around 09z Friday and pushing east-southeast per the
Temps will slowly slide through the 70s across the lower susq
valleylate this evening, and range from the mid 60s to low 70s
across the SW mtns early tonight. Look for partial clearing
toward daybreak near and just to the north of I-80 with mins in
the mid 50s to l60s, while the ncent and northwest mountains of the
state will stay mainly clear, yielding chilly min temps in the
mid to upper 40s in vicinity of kbfd thanks to strong radiational cooling
from light wind, much lower dewpoints advecting southeast into the
Short term /6 am Friday morning through 6 PM Friday/...
the front is still progged to stall out 100mi or so south of the
Mason-Dixon line. But, much drier air will spread through all
the area and bring dry and cooler conditions for Friday (and all
the weekend). Any early fog (and/or sprinkles in the south) will
dissipate soon after sunrise. Maxes will hold in the 60s over
the highest hill tops but still get into the u70s in the larger
cities of the susq valley.
Long term /Friday night through Thursday/...
an extensive area of high pressure will bring fair and dry
weather to central PA this weekend. Weekend temperatures should
be near to slightly below normal for late-August, with a dry
airmass providing pleasantly warm afternoons and comfortable
Heading into next week, the question will be how quickly return
flow develops and brings moisture back into the area. The GFS
continues to be a bit more bullish, bringing showers back into
the region Monday, while the European model (ecmwf) delays the wet weather until
Tuesday. Given the uncertainty, went with a model blend and
gradually increase pops Monday into Tuesday. Pops should peak
Wednesday with a frontal passage, with a drying trend for the
later part of next week.
The temperature forecast becomes less certain early next week,
as models develop southeasterly low-level flow that may advect
clouds into the area and result in lower high temps Monday and
Tuesday. Following the mid-week frontal passage, cooler and
drier weather should return late next week.
Aviation /00z Friday through Tuesday/...
23z surface analysis places a cold front in the vicinity of
I-80. A shower and accompanying brief vis reduction remains
possible this evening over the southern half of the state, as
this front sinks south. At klns, a gusty thunderstorm appears
likely just before 00z.
A concern later tonight will be the possibility of low cigs over
the Laurel Highlands. Residual, Post-frontal low level moisture,
combined with upsloping northwest flow, could potentially yield
IFR cigs in vicinity of kjst later this evening. The threat of
low cigs should subside toward dawn, as drier air works
southward into the region.
Another area of concern will be the northwest mountains, where
mostly clear skies and a nearly calm wind is likely to promote
patchy late night fog.
Any early fog over northwest PA should dissipate shortly after
12z. Otherwise, confidence is high for widespread VFR
conditions and light wind Friday, as high pressure and
associated dry air mass build into the region.
Sat-sun...am fog possible.
Mon...am fog possible. Southeast low level flow, low clouds poss.
Tue...rain showers poss.