Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
149 am EST Monday Dec 22 2014
a weak low pressure system will move northward along the middle
Atlantic coast on Monday. A vigorous storm system will push a
cold front across the commonwealth on Christmas evening bringing
widespread showers and even a chance for thunderstorms. Windy and
colder conditions will follow with scattered snow showers across
the west and north for Christmas day. Dry and seasonable
conditions are expected for Friday and Saturday before more
unsettled weather arrives for the second half of the weekend.
Near term /until 7 am this morning/...
infrared loop shows mclear skies across the bulk of central PA at 06z.
Increasingly moist southeasterly flow will likely cause stratus to work
into the high terrain of Somerset/Bedford cos toward dawn...as
well as the the high terrain over Sullivan/Schuylkill cos. Temperatures on
track to bottom out in the l20s over most of the area.
Short term /7 am this morning through 6 PM Tuesday/...
920 PM update...
have continued to mention some freezing rain for The Laurels/SC mountains and up
into the alleghenies...and along the northern fringe of the very light
precipitation expected to move in from the S late Monday aftn/evening. Sref
probability of freezing rain are very high in The Laurels and alleghenies for the
evening and Monday night. But the precipitation is still uncertain enough to
keep probability of precipitation in the high-chance range...tapering off rather quickly west of
rte 219. Therefore...still no advisory to be posted this early/at this
time horizon due to the low certainty of occurrence of precipitation let
alone freezing rain accretions.
increasing low level moisture is expected to bring some spitty/spotty
nuisance type precipitation across southern and southeastern areas
on Monday...mainly afternoon. Nam12 remains aggressive in pushing
moisture north of the Mason Dixon line after 12z...an
outlier...which would introduce precipitation type issues given residual
marginal cold air Monday morning. Continue to downplay that model
and solution...and favor a consensus later arrival of light
precipitation...which would still produce some patchy mixed precipitation at the
onset. Confidence still too low on this for any advisory
consideration at this time/range.
Depending upon timing of arrival...areas which may be most
susceptible to brief -fzra Monday afternoon would be over parts of
the central and south central mountains. Still monitoring this low
probability event at this time...and will mention low chances in
Long term /Tuesday night through Sunday/...
for Monday night...did not change a lot. NAM model looks a
little wet...so did not up probability of precipitation a lot. Went for a mix of
rain and freezing rain...precipitation amts not much more than .O1.
More like a drizzle. Still third period...too early for an
advisory. The moist southeasterly flow off the Atlantic and associated
orographic forcing of shallow moisture layer will linger into
Tuesday morning...but should edge to the east during the day. After
having lows in the 31-32 degree range...temperatures should edge up some
during the day on Tuesday.
Did not change a lot for Tuesday...some rain during the day
into Tuesday night...but not all the time. Low rather far to
the west for strong flow to move colder air out.
The most significant forecast issue in the long term remains the
evolution of deep trough and associated surface low to our west 24-25
December. Strong southerly flow ahead of this system will bring
some of the warmer air into the region on Wednesday...as many
low-level temperature and moisture fields rise well above their
seasonal values. This implies warmer temperatures on Wednesday...as the
shallow cold air scours out east of the mountains.
New models slow front some...thus did up probability of precipitation Wednesday night and
go all rain.
Colder air works in for Christmas...but snow showers will
be mainly confined to the western mountains...and not real
Milder air works in for Friday on SW flow.
Colder air again for later in the weekend...as another
cold front moves across the area.
Aviation /07z Monday through Friday/...
the pattern continues as stratocu is trapped under an inversion
through mainly the north. The rest of the region has cleared. The
question overnight is that whether any of the weak southerly flow
allows for stratocu to thicken. With light winds
Combination of retreating high pressure over New England and weak
low lifting up the East Coast will bring a gradually increasing
moist southeasterly flow into central PA late tonight and especially Monday.
Anticipate that we/ll see redevelopment/reinforcement of the
stratocu deck over The Spine of the Appalachians /from kjst-kbfd/
overnight...though any middle clouds will reduce formation. Expect
MVFR possible at jst and aoo between 09 to 12z. Though IFR should
continue at bfd overnight into tomorrow.
The increasing moisture...combined with lg scale forcing ahead of
shortwave lifting out the Ohio Valley...could spread a bit of
light precipitation into southern PA Monday PM.
Monday...ceiling reductions west. Restrictions developing east. Light
rain poss south...freezing rain poss western higher terrain. Becoming
Tuesday...low ceilings with drizzle/light rain likely. Breezy.
Wednesday...periods of rain along with widespread reductions. Windy
with low level wind shear.
Thursday...windy and colder with scattered MVFR ceilings and -shsn. Low level wind shear.
Friday...fair and mostly VFR.