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Area forecast discussion 
National Weather Service State College PA
1034 am EDT Wednesday Jul 27 2016

Synopsis...
a weak front will remain along or just to the south of the
commonwealth through tonight, as high pressure maintains warm and
mainly dry conditions. An area of low pressure approaching from
the west is likely to lift through the region on Friday.

&&

Near term /until 6 PM this evening/...

Satellite shows some clouds along southern tier. Nothing of note
on radar. For consistency and collaboration showed some slight
chance showers along border. No quantitative precipitation forecast and slight pops numbers.

Most of the broken to overcast cloud decks should stay close to
PA/Maryland border. So farther north in the shallow drier air the more
sun. Dew points today mainly in the 60s so a bit of relief.
Temperatures probably close in most areas to yesterdays maximums.

Temperatures were mainly a model blend with some hrrrv1
temperatures added for texture. Hrrrv1 is too warm for daytime
highs but shows upper 80s in northwest and northwest mountains,
near 90 central and Southwest Mountains, and mid-upper 90s in
southeast. Hrrrv1 has run about 2-3f too warm the past week or so.

Many locations have seen 5 to 7 days of high temperatures of 90 or
greater recently. A rather enduring heat episode.

&&

Short term /6 PM this evening through 6 PM Thursday/...

Most guidance holds off the rain until Thursday afternoon. The
ncar efs and hrrrv2 imply this too. This evening should be
rain free. Clouds in southern areas will increase this evening and
overnight and chance of showers will increase in southwest after
midnight.

The ncar efs implies showers in southwestern areas a few hours
after 5 am Thursday morning. The rain spreads to the east and
north during the day. This is close to the gefs viewed in 3-hour
increments showing rain by 2 PM in southwest and over most of
central and southern areas by 7 PM. Ncar efs may be a bit faster
with the lighter amounts.

Suffice to say chance of showers in extreme southwest in morning
with increasing chance of rain into afternoon spreading across the
region. Lower pops in northernmost areas.

Most guidance implies a better slug of rain possible overnight
Thursday into Friday, beyond the scope of this forecast period
(see below).

&&

Long term /Thursday night through Tuesday/...

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-
Fri timeframe.

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 east-northeast 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 thunderstorms and rain. 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
shield.

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
cyclonicly 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
region.

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 thunderstorms and rain 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 /14z Wednesday through Sunday/...
VFR most of the day today. Relatively light winds.

Flying conditions will change Thursday into Friday as a frontal
wave brings rain and showers to the region. Expect increased
chance of MVFR and IFR Thursday into Friday with areas of rain and
isolated thunderstorms.

Conditions should improve Friday into Saturday.

Outlook...

Thu-Fri...areas of MVFR and IFR in rain and isolated thunderstorms
Sat-sun...mainly VFR.

&&

Ctp watches/warnings/advisories...
none.

&&

$$
Synopsis...devoir
near term...grumm
short term...grumm/devoir
long term...Lambert/gartner
aviation...grumm/dangelo

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