Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 272006
Area Forecast Discussion
National Weather Service State College PA
406 PM EDT Mon Mar 27 2017
An area of low pressure will move along or just south of the
Mason-Dixon line late tonight and Tuesday. High pressure will
build down out of southern Canada and bring cooler and drier
weather for Wednesday and Thursday.
A new storm system will approach for the end of this week with
the potential for more inclement weather.
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
The drier air has scoured out the low clouds over all but the
far north and much of the mid and lower Susq Valley where the
cold air damming is tenacious. Even there however the milder and
drier air should mix down by mid afternoon, at least for a
brief time anyway.
Despite the projections of some modest instability in the RAP,
the HRRR keeps a lid on things for the rest of the day. So I
lowered the already low chances for a pop up shower or
thunderstorm over the far south, especially in the areas still
plagued by the cool-moist maritime airmass.
Clouds will tend to return with a renewed chance of showers
once again tonight as the next wave of low pressure moves into
Ohio. Lows will be very mild in the 40s to lower 50s.
.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
Latest NAM/GFS show the surface wave taking a track over or just
south of the PA-MD border during the day Tuesday bringing
occasional showers that will taper off from NW to SE during the
afternoon. The guidance once again shows the development of
some instability over southern areas so a thunderstorm cannot
be ruled out. It will likely be subject more to the amount of
sunshine that can develop than dynamic forcing.
It will be another mild day in the 60s in most locations.
.LONG TERM /TUESDAY NIGHT THROUGH MONDAY/...
-- Changed Discussion --The long term period will start with a frontal system and
associated precipitation exiting the region and heights building
aloft. Building high pressure will push the warm moist air off
to our south Tuesday night into Wednesday. Wednesday should be
a relatively nice day (though with some mdt northerly wind gusts
at times, as high pressure builds in from the northwest. The
dry air and high pressure are in all of the most recent
guidance, implying Wednesday and Thursday should be relatively
High pressure, dry air, and normal to slightly below normal 850
hPa and 925 hPa temperatures imply near normal daytime highs.
Most of the 26/00-06Z U.S. and int`l model guidance (and EFS)
indicates more of southern...shearing storm track for late in
the week...thanks to a stronger and more wwd position of a deep
nrn stream vortex across the Canadian Maritimes.
The trend of the big model discrepancy for late this week and
this weekend (between the GFS and EC over the past several days)
has trended toward the GFS and its ENS members with southern
stream energy and its moisture being prevented from amplifying
with an associated storm track to our west.
Rather, what we see is a shift of the primary southern stream
sfc low track to our south as the potent midweek southern stream
sfc/upper low (that will be trying to take the turn northeast
across the Mid Miss Valley twd the Great Lakes) encounters great
resistance from the notably stronger WNW upper jet core
defining the northern stream that will be situated from the
Upper Glakes to the Mid Atl Coast.
With this type of consensus storm track, pops will be somewhat
less for Friday and Saturday (compared to a heavily weighted
EC/ECENS solution) and limited to mainly the southern half of PA
where some rain (or even an elevation-dependent rain/wet snow
mix) with expansive cooler and drier air north of PA.
-- End Changed Discussion --
.AVIATION /20Z MONDAY THROUGH SATURDAY/...
The drier air is mixing into central PA quickly as of early
afternoon. The exception is over the Susq Valley where MVFR/IFR
conditions continue. Even here however the drier air will manage
to invade between about 3 and 5 pm.
Unfortunately the VFR conditions this evening will deteriorate
once again overnight as a new storm system spreads showers our
Widespread IFR/MVFR will be the rule Tuesday along with
occasional rain showers and even the small chance of an
afternoon thunderstorm over the south.
Wed...MVFR NW 1/3 becoming VFR.
Thu...VFR/No sig wx.
Thurs night-Sat...Sub-VFR restrictions/rain likely.
NEAR TERM...La Corte
SHORT TERM...La Corte