Lancaster, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

759
FXUS61 KCTP 221217
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
717 AM EST Sun Dec 22 2024

.SYNOPSIS...
High pressure over the Great Lakes will build east across
Pennsylvania today and tonight, then a weak area of low pressure
will track north of the state Monday night into early Tuesday.
A pair of weakening shortwaves are likely to ride the northern
periphery of a building ridge over PA the second half of next
week, as a large surface high remains anchored north of New
England.

&&

.NEAR TERM /THROUGH TONIGHT/...
Dwindling lake effect flurries are expected early this morning
over the Alleghenies, as high pressure approaches from the Great
Lakes. Stratocu, which covers the northern and western portion
of the forecast area at 11Z, should begin to break up, as
inversion heights fall. Latest model RH profiles support mostly
sunny skies over all but parts of Warren County by this
afternoon.

Model soundings become mixed this afternoon to 900mb, where
temps around -14C support highs ranging from the mid teens over
the Mtns north of KIPT, to the upper 20s in the lower elevations
along the Mason Dixon Line. Even though highs will be several
degrees below those of Saturday, the combination of sunshine and
lighter winds may actually make it slightly more pleasant to be
outside.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
High pressure is progged to build over PA tonight, providing
nearly ideal conditions for radiational cooling with clear
skies, a calm wind and a fresh snowcover over parts of the area.
Have therefore undercut NBM min temps by a few degrees. Tonight
should undoubtedly be the coldest yet this winter, with daybreak
readings likely ranging from the single digits below zero in the
coldest hollows north of KIPT, to around 10 above over the
southern tier counties.

A return southerly flow behind the departing surface high will
help temperatures rebound slightly on Monday as high clouds
stream in ahead of an upstream shortwave over the W Grt Lks.
GEFS 2m temps indicate maxtemps will remain several degrees
below average.

The upstream shortwave is progged to pass just north of PA
Monday night into early Tuesday. The strongest forcing with this
feature should remain north of the area and moisture return
along the attendant low level jet is unimpressive. Therefore,
expect only some very light overrunning snow or flurries Monday
night into early Tuesday. The 00Z EPS indicates the NW Mtns are
best situated to see an inch or so of accumulation due to
proximity to the shortwave and orographic forcing from an
upsloping SSW flow. Model soundings indicate there is some risk
for a bit of very light freezing rain over the Lower Susq Valley
around 12Z Tuesday, but it is uncertain whether measurable precip
even reaches that far south.

The best forcing and deepest moisture should have passed PA by
late Tuesday morning. However, residual low level moisture
ascending the Alleghenies could result in spotty very light
snow/drizzle into the afternoon over the western part of the
forecast area.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
On the large-scale, the amplified, cold eastern
Canadian/northeastern CONUS upper trough dominating at the
present time should be a thing of the past by Christmas Day, as
this feature lifts out into the northern Atlantic. It will
replaced by building heights and a generally more zonal flow
pattern aloft. This translates into more seasonable temperatures
for late December across PA, even trending above climo towards
next weekend.

As for the sensible weather, there is increasing confidence that
surface high pressure from southeastern Canada down into the
northeastern U.S. will keep the weather dry for the Commonwealth
from Christmas Day into at least Thursday.

Uncertainty grows later in the week, as low-level easterly flow
and the approach of weak short-wave energy from the Midwest
could bring bouts of light precipitation, especially for
southern and western sections of the state. At this early
juncture, light rain appears to be the most probable
precipitation type, but pockets of light wintry mix are not by
any means off the table.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
As daybreak subsidence and dry air should be moving into
region. JST and BFD are still the two most likely sites to see
lower flight categories from low clouds, but they will be
borderline MVFR/VFR and shouldn`t last beyond 16Z. All other
sites should experience clear skies or clouds scattering out
throughout the day and clear skies coming into play by Sunday
afternoon.

Light winds and clear skies are expected for Sunday night into
the first part of Monday.

Main issue for the area after Monday would be for lower
CIGS and even some mixed precipitation from time to time,
mainly after early Monday evening, as a milder and higher
dewpoint airmass works into the area.

Outlook...

Mon...No sig wx.

Tue...Snow enters W PA AM, overspreads area by afternoon.

Wed...No sig wx.

Wed Night...Patchy freezing rain possible.

Thu...Light rain possible south.

&&

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

&&

$$

SYNOPSIS...Fitzgerald
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Jurewicz
AVIATION...Bowen