Area Forecast Discussion
Issued by NWS State College, PA
FXUS61 KCTP 272118
Area Forecast Discussion
National Weather Service State College PA
518 PM EDT WED JUL 27 2016
A weak trough to our north and the subtropical ridge to our south
have setup a frontal boundary just to our south. This boundary
will move northward as a shortwave moves over the ridge Thursday
night. This should produce some rain Thursday into Friday. Behind
this system system slightly cooler air aloft moves over the
region. But the ridge may begin to build to our west again early
.NEAR TERM /UNTIL 10 PM THIS EVENING/...
Stayed close to guidance values nudging forecast with blend and
HRRR. Cooler to the north with open cell cumulus in northern
Pennsylvania. Warmer and more humid to south with some clouds
moving over the northern edge of the low-level frontal boundary to
The HRRRV2 shows little or no QPF with a few spotty rogue elements
and the HRRRV1 is tad more active. So kept slight chance showers
in extreme southwest. Lower than hydrostatic model blend PoPs
which were in the 20-30 percent range.
Any showers would be really isolated and weak. Have no QPF.
Central and northern along with eastern areas will be partly
cloudy though the cumulus will dissipate close to sunset. Higher
clouds in westerly flow aloft will persist.
Most areas on south-southeast will likely top 90 again today. Many
locations are close or have already done so.
.SHORT TERM /10 PM THIS EVENING THROUGH 6 PM THURSDAY/...
Guidance implies areas of patchy fog overnight. Better chance in
western areas. Clouds slowly increase southwest to northeast
Overnight lows mainly near 60 in northwest to lower 70s southeast.
Tomorrow clouds increase in southern and central areas. Increased
moisture will produce haze. Best chance rain in southwestern
The HRRRV2 keeps the rain out of our area through 0300 UTC tonight
and implies it is well to our west back over KY. Tweaked grids
with new 12Z blends which had slight chance PoPs overnight in
southwest increasing to chance in the morning. Chance of rain will
increase southwest to northeast during the day. But most guidance
continues to imply most of northern PA should be rain free most of
the day. Best chance in south and southwest.
Higher PoPs are likely in the next period.
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
In the medium to long-range period...conditions slowly revert to
near normal in temp and precip as several chunks of short wave
energy in the westerly flow aloft helps to carve out a mean 500 mb
trough axis over the Glakes and Ohio Valley region during the Thu-
The peak in unsettled weather (with perhaps some periods of down-
right rainy conditions) occurs Thursday night and Friday as a
well-defined wave of sfc-850 mb low pressure lifts ENE out of the
Ohio Valley and heads across the I-95 Megalopolis.
Followed a blend of EC/GEFS/superblend and NBM guidance for that
particular 24-36 hour period to arrive at likely pops for rain and
scattered TSRA. Some uncertainty in timing and areal coverage of
the convection led us to undercut the NBM by 10-20 percent for
now, recognizing issues with large scale model convective
parameterization schemes (and subsequent exaggeration of the areal
coverage and broader qpf amounts) means that we`ll likely see more
concentrated areas/bands of heavy convection, compared to the
model depicted, larger cold season stratiform look to the precip
Portions of Southern and Central PA...close to the track of the
1006-1008 mb sfc low will likely see some localized heavy 1-2
inch,12-24 hour rainfall amounts by Friday afternoon...with even
the potential for some pinpoint heavier amounts from embedded
TSRA, as a tongue of 2 inch pwat air lifts north and wraps
cyclonically into sern PA and the Lower Susq Valley.
For later Friday through the upcoming weekend, a large area of
high pressure (1020-1024 mb) near the border of southern Quebec
and Ontario will try to push drier air south into the Mid Atlantic
Another...apparently weaker wave of low pressure at the sfc and
aloft lifts NE out of the Ohio Valley over the weekend and brings
an enhanced chc for showers. Slight diffs in timing/location exist
between the EC/GEFS and NBM guidance. However...the target period
for the best chc of showers and isolated to sctd TSRA appears to
be late Sat into Sunday.
Afterward, heights begin to rise from the southwest, accompanied
by a ridge of surface high pressure building east into PA with
mainly dry conditions and a rebound in temps for early next week.
.AVIATION /21Z WEDNESDAY THROUGH MONDAY/...
VFR conditions will prevail into early tonight. Patchy fog will
develop in the valleys and elevated valleys of central PA. Expect
areas of MVFR and IFR to develop near or shortly after midnight.
Fog will lift early Thursday. Rain and an isolated thunderstorm
could move into southwestern areas Thursday morning and afternoon.
This would produce areas of MVFR and perhaps IFR conditions in
More MVFR and IFR conditions possible overnight Thursday into
Friday morning with the potential for rain/thunderstorms and
Conditions should improve Friday into Saturday.
THU-FRI...areas MVFR and IFR in Rain/TSTMS and patchy fog