Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 150017
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
717 PM EST Thu Dec 14 2017

.SYNOPSIS...
A weak ridge of high pressure will slide across the region tonight
with cold, but mainly dry conditions.

Another clipper will move north of the region overnight Friday
and Saturday morning followed by high pressure and a brief
moderating trend in the temperature Sunday.

A series of cold fronts will move across the area late Sunday
into Wednesday. Windy and colder temperatures will follow.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Radar showing a few light lake effect snow showers/flurries
across the Warren/Mckean counties early this evening. However,
boundary layer flow is progged to back to the southwest shortly,
shifting remaining lake effect activity north of the border.

Otherwise, fair and chilly conditions overnight, as surface high
drifts over the state. Some increasing high clouds expected
overnight associated with waa aloft ahead of approaching
shortwave. However, light winds and snow cover should allow
readings to drop into the single digits north to upper teens
south.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
After a cold start temperatures will recover only to highs near 20
in the north to around freezing in the extreme southeast. Clouds
and snow showers will be most likely late in the day over the
Allegheny Plateau, as a shortwave turns the flow more NWLY and
brings a chance of Lake Effect back into the areas normally
affected this time of year. Developing low off the Mid Atlantic
coast could potentially graze the extreme southeast corner of
the forecast area during the afternoon, so have included low
POPs down there for a period of light snow.

&&

.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
The period starts out with below normal 500 hPa heights and
below normal 850 hPa temperatures. The heights and temperatures
rise to above normal values over the northeastern United States
Sunday as a strong ridge retrogrades to our south. The really
warm air should stay to our southeast. The heights and
temperatures settle back toward normal Tuesday and Wednesday at
500 hPa and 850 hPa respectively.

Temperatures may rebound Thursday ahead of another frontal
system. Overall with the strong ridge to our southeast the
fronts do not get too far south.

Saturday we should still be in the cold air with some LES based
snow activity in the northwest. As the high retreats to our east
temperatures should begin to rebound and the snow showers in the
northwest diminish.

Sunday into Monday a strong shortwave to our north will help
bring in warmer air. We may be cold air dammed near the surface
so the +1 to -2C air at 850 hPa may not translate to a warm
boundary layer. The warm advection should bring snow and snow to
rain in the south but QPF amounts are low and EFS based POPS are
not very high in central and southern areas.

As this northern stream wave zips by to our north it should drag
cold air back into the region Tuesday into Wednesday. The
northwest flow triggers snow in relatively high POPS in NW PA
due to LES. This cold surge should be relatively fleeting and
high pressure and a potential surge of warmer air in the
NAEFS/GEFS. This suggests relatively warmer on Thursday.

The Warm advection and approaching cold front will likely
produce increased potential for snow in NW Thursday into Friday.
Farther south any precipitation would likely be mixed or rain.

A strong frontal boundary will likely push another surge of
cold air into the region Friday into Saturday.

At this time and recent GEFS/CMCE and combined NAEFS runs keep
the strong ridge suppressed to our south. This keeps the warm
air from getting here. This keeps us relatively dry with all
the significant QPF events suppressed to our south.

There is considerable spread in the ensemble members. And we
have seen run-to-run variations in the solutions with the strong
southwest Atlantic ridge. The NAEFS deeps reforming vortex over
east-central Canada and maintains the sharp ridge over
northwestern North America. This seems to keep us in or on the
edge of cold air intrusions. Thus so far single model runs of
big warm ups appear to disappear in the ensembles.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
* Cloud/Ceiling info will be missing at KBFD until new part can
  be installed *

All Central Pennsylvania airfields now reporting VFR
conditions, although appears there are still some patchy MVFR
ceilings as depicted on satellite across the northern mountains.

Overnight will be clear to partly cloudy and cold with some
MVFR ceilings expected to move back into the higher elevation
terminals of the west and north. The chance of snow showers will
be on the increase Friday, mainly over the north.


Outlook...

Fri...MVFR with snow showers north and west mountains, mainly
VFR elsewhere.

Sat...Scattered snow showers and local restrictions NW/Laurels.

Sun-Mon...Mainly VFR.

Tue...mainly VFR, but possible restrictions in the western and
northern mountains in snow showers.

&&

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

&&

$$
SYNOPSIS...La Corte
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald/La Corte
LONG TERM...Grumm
AVIATION...Jung



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