Harrisburg, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

846
FXUS61 KCTP 230417
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1117 PM EST Fri Nov 22 2024

.SYNOPSIS...
* Breezy with showers over the western Alleghenies to start the
  weekend, followed by improving conditions on Sunday
* Windy with rain and snow showers Monday night into Tuesday;
  another potential bout of winter weather possible for
  Thanksgiving Day

&&

.NEAR TERM /UNTIL 7 AM SATURDAY MORNING/...
04Z radar loop shows the back edge of the steady precipitation
associated with TROWAL/frontogenetic forcing is now exiting
Southern Somerset County. A few light rain/snow showers remain
over the area late this evening associated with low level
instability under the upper low, which is over Eastern PA. As
the upper low weakens and drifts east of the state, expect the
risk of additional showers to wane overnight.

Large scale subsidence arriving behind the exiting upper low,
combined with a downsloping northwest flow should yield
breaking clouds late tonight east of the Alleghenies. However, model
soundings indicate upsloping flow will result in persistent low
clouds across the W Mtns. Weak low level cold advection late
tonight should translate to slowly falling temps with readings
at dawn likely in the low to mid 30s.

&&

.SHORT TERM /7 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
The northwest flow behind the departing upper low is just cold
enough to support lake effect Saturday. Model soundings show
inversion heights peaking late morning through the afternoon
hours, coincident with the passage of a weak upper level
shortwave. Have ramped POPs upward toward the HREF values due to
nearly saturated model soundings in the 0-2km layer, which
should support light precip in most spots across the Allegheny
Plateau. A few wet snowflakes are possible on the higher
ridgetops of the Laurel Highlands Sat morning. Otherwise,
progged thermal profiles are too warm for anything but rain
showers.

Model RH profiles support a partly to mostly sunny start to
Saturday east (downwind) of the Alleghenies. However, warm
advection ahead of the approaching shortwave should result in
increasing clouds by afternoon.

A fairly tight gradient west of intense low pressure over Nova
Scotia will result in gusty northwest winds across the area
Saturday. Bufkit soundings indicate frequent gusts of 20-25kts
are likely. GEFS 2m temp anomalies support near seasonable high
temps Saturday, ranging from the low 40s over the highest
elevations of the Alleghenies, to the low 50s in the Lower Susq
Valley.

&&

.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
* Winter Weather may impact travel on Thanksgiving Day across
  Central PA

A weak shortwave diving across the Eastern Grt Lks should
sustain scattered lake effect rain showers over the Allegheny
Plateau into early Sunday, then ridging building into PA should
support fair and milder conditions Sunday PM through Monday AM.
All guidance currently tracks a cold front through the region
Monday night, preceded by a round of rain showers Monday PM.
CFROPA in the late night/early morning time-frame will probably
keep the chc for thunder low, but would not be surprised to hear
a rumble or two since the front is potent and 8H temps drop 15C
over 12 hrs at UNV. Could be a gusty passage, too (potential
NCFRB) due to 8H winds from 240deg at >=50kt per GFS. Tues looks
mainly dry under high pressure. Perhaps a SHSN NW.

Wed now looks fairly good for travel across PA with ridging
building over the state. A bit of lingering lake effect snow
is possible over the NW Mtns early in the day. Much of the
medium range model guidance tracks an area of low pressure
northeast from the Lower Miss Valley late next week, spreading
precipitation across PA for Thanksgiving Day. A track south of
the Mason Dixon Line suggests there will be enough cold air
present for snow over at least Northern PA. However, there
remains plenty of uncertainty this far out and a significant
number of ensemble members are weaker and further south with the
area of low pressure. Will continue to monitor the forecast as
confidence is expected to increase over the next 2 to 3 days.

Current timing and placement of mass features should allow for
gusty winds and drying on Friday except in the northern
Alleghenies where the cold air and WNW flow will generate
lake effect SHSN which may linger thru much of next weekend
(days 7-9). A shot of even colder air comes along late in the
weekend, and looks like a pattern favorable for snow squalls.

&&

.AVIATION /04Z SATURDAY THROUGH WEDNESDAY/...
The main area of rain and snow continues to push southwest this
evening and steady rain and snow is mainly confined to areas
near and southwest of JST and AOO. Ceilings have risen over the
past few hours to MVFR for areas east of the Allegheny Front and
further improvement to VFR is possible towards daybreak
(especially at MDT and LNS). Moderate to heavy snow continues at
JST as of 00Z and is leading LIFR restrictions. This will
continue for a few more hours before drier air moves in
overnight and brings an end to steady snowfall. While
visibilities will improve, ceilings will remain IFR. Gusty winds
20-30kt from 280-320 degrees will continue through Saturday.
Showers will develop once again Saturday afternoon near BFD and
JST and could reach as far east as AOO and UNV.

Outlook...

Sun...MVFR cigs NW 1/2 impacting KBFD and KJST. VFR elsewhere.

Mon-Tue...Strong CFROPA Monday night with rain and potential
LLWS followed by strong winds and snow showers.

Wed...Not as windy with MVFR to VFR cigs; mixed precip could
reach the southwest airspace by 12Z Thu.

&&

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

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald/Dangelo
AVIATION...Steinbugl/Bauco