Scientific Forecaster Discussion
fxus61 kctp 212313
Area forecast discussion
National Weather Service State College PA
713 PM EDT Thu Sep 21 2017
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 Friday morning/...
thin high clouds associated with Jose have covered much of the
eastern half of PA this evening as it 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 Friday morning through 6 PM Friday/...
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-
Long term /Friday 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
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 probability of precipitation.
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 southeast Metro areas.
Min temps may cool off slightly for this weekend thanks to deep
dry air and a light north to northwest llvl flow of drier dewpoint air at
Aviation /23z Thursday through Tuesday/...
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 could temper the radiational cooling and fog
potential. However, believe a period of IFR/LIFR conditions is
likely at kipt and possible (30-50 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
Sat-Mon...am valley fog. Otherwise VFR.
astronomical fall/autumnal equinox begins at 4:02 PM Friday
September 22, 2017.