Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 220536
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
136 AM EDT Fri Sep 22 2017

.SYNOPSIS...
A ridge of high pressure at the surface and aloft will stay
anchored across the Lower Great Lakes, Ohio Valley and
Northeastern States through at least Tuesday. This will
continue of dry and unseasonably warm weather to Pennsylvania.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Thin high clouds associated with Jose have covered all but the
western third of PA this evening...as TS Jose continues to churn
well off of the southeast New England coast. Aside from these
high clouds, the only other sensible weather will be fog
developing again overnight, mainly in the valleys. Going with
just a deg or two cooler tonight than last night, as the drying
of the airmass today may allow things to cool off just slightly
more tonight. The subsidence inversion height is lowering
slightly hour by hour, so mixing during the day on Fri should
not be as deep as today. This might make reaching today`s maxes
a little challenging, but it is tough to go away from a
persistence forecast in this ever-so- stagnant pattern.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/...
Ridge, ridge and more ridge. The subsidence inversion height is
lowering slightly hour by hour, so mixing during the day on Fri
should not be as deep as today. This might make reaching
today`s (thurs) maxes again a little challenging, but it is
tough to go away from a persistence forecast in this ever-so-
stagnant pattern.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
For this weekend and early next week, the pattern remains
stable as a building ridge continues to stifle any convection.
Weak flow at night should allow for valley fog to form nightly
and to greet morning commuters. The overall consensus in the
models through the weekend is for the 590 dam closed 500 hPa
high will drift slowly out of the midwest states, and become
centered over western PA by late this weekend through early next
week.

Ensemble temperatures are in general consensus and high temps
through the weekend will be 10-15F above normal with little or
no chance of rain until Monday at the very earliest. There are
hints that what was left of Jose could bring moisture and thus
some rainfall through Monday into Tuesday. However there
continues to be model variability so have only chance POPS.

Lows early each morning will be consistently in the mid and
upper 50s across the northern and western mtns, to lower 60s in
the larger SE metro areas.

Min temps may cool off slightly for this weekend thanks to deep
dry air and a light N to NW llvl flow of drier dewpoint air at
the sfc.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
Just minor adjustments for the 06Z TAFS.

Did edge off fog some, not even seeing any fog at foggy sites
such as SEG as of 1 AM. The combination of high clouds, a
little breeze at times, and mainly less moisture in the airmass
than earlier in the week, will result in less fog this morning,
than earlier in the week. This was the case yesterday morning.

More detail below.

Light wind will allow valley fog to form across northern PA
overnight. Model guidance and persistence forecasting indicate
KBFD is very likely to experience IFR/LIFR conditions early
Friday morning. Further south, model guidance suggests a veil of
high clouds may become thick enough to temper the radiational
cooling and fog potential. However, based on falling temps and
dewpoint depressions this evening, believe a period of IFR/LIFR
conditions is likely at KIPT and possible (~50 pct) at KUNV/KAOO
around dawn. The odds of of significant reductions at
KJST/KLNS/KMDT appear very low.

Any early fog should burn off between 13Z-15Z, then model data
supports a near certainty of VFR conditions and light wind
everywhere for Friday afternoon, as high pressure remains over
the region.

.Outlook...

Sat-Tue...Patchy AM valley fog possible.

&&

.CLIMATE...
Astronomical Fall/Autumnal Equinox begins at 4:02 PM Friday
September 22, 2017.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Dangelo
NEAR TERM...DeVoir
SHORT TERM...Dangelo
LONG TERM...Lambert/Gartner
AVIATION...Fitzgerald/Martin
CLIMATE...Steinbugl



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