Harrisburg, Pennsylvania 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

967
FXUS61 KCTP 130540
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1240 AM EST Wed Nov 13 2024

.SYNOPSIS...
High pressure will continue to slide overhead tonight and
continue moving to the east on Wednesday. A weakening low
pressure system approaching from the Midwest is likely to track
into the region Thursday, bringing some light rain and even some
wet snowflakes on the higher elevations. High pressure returns
for the weekend.

&&

.NEAR TERM /THROUGH TODAY/...
Main forecast dilemma for tonight is whether fog will try to
form in the valleys. Probabalistic and MOS guidance says no, but
light wind and cool temps should allow for some. Wind earlier
today likely dried things out well despite recent precip. Will
hold off on adding a mention of fog for now, since forecaster
personal bias is not strong enough science to add some in. Temps
are on track and the few clouds percolating off the Finger
Lakes are well-forecast, too.

Prev...
Sky is mainly clear and the wind has started to slacken already.
This will allow temperatures to fall a few degrees below NBM
guidance. Expect a widespread hard freeze over the forecast
area, with min temps ranging from the upper teens in the coldest
hollows of Northern PA, to around 30F in the more urbanized
spots of the Lower Susq Valley.

Upper level ridge pushes into the region on Wednesday with high
pressure remaining in control at the surface. Clear and dry
conditions will continue throughout the day. Easterly flow off
the Atlantic will keep temperatures steady in the upper 40s to
lower 50s across the region. Similar conditions will continue
into the overnight period with clear skies and light winds.
Temperatures will again fall a few degrees below model guidance
with lows in the upper 20s to low 30s across eastern PA.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY/...
Main forecast concerns in the short term are focused on the
next chance of precipitation arriving Thursday and moving
east/southeast out of the area on Friday...with the threat of
snow mixing in with rain from the Laurel Highlands through the
Central Mtns and into the northern Allegheny Plateau during the
morning hours of Thursday.

A sharp, high-amplitude trough over the central US Wed night
will be shifting to the east across the southern Great Lakes and
Ohio Valley region early Thu morning and phasing with a
relatively weak plume of deep moisture from the Gulf of Mexico
over the southern portions of the wave. This wave undergoes a
period of weakening with a loss of moisture by Thursday morning.
A blocking low pressure system off the coast of Nova Scotia
will squeeze the ridge axis aligned along the East Coast, and
eventually push the incoming short wave to the southeast through
the mid Atlantic region. An area of rain is expected (60-80%)
to move in between 8-11 AM and slowly spread to the east/se over
central PA through the afternoon and evening hours.

Precipitation types will be a challenge during the morning
hours Thursday as there seems to be a general consensus of weak
cold-air damming along the eastern side of the Laurel
Highlands/Allegheny Mtns. There is a 40-60% chance of snow
mixing in before noon Thu across elevations above 1400 feet.
There could be some light accumulations (0.2" or less), but
confidence is less than 20%. There is also a very low chance
(less than 10%) of brief light freezing rain over the higher
terrain of Somerset and Cambria Counties, but will be very
short-lived if it does transpire. The wintry mix should not last
very long as temperatures climb into the upper 30s and 40s in
the afternoon. The rain will linger and eventually move out late
Thursday night and Friday morning.

A dry and relatively mild northerly flow will set up later in
the day Friday with skies staying mostly cloudy over western PA
and becoming mostly clear to the east. This will lead to
afternoon high temperatures on Friday into the upper 40s in the
high elevations and northern tier of PA, and into the mid 50s to
the south and east.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Upper level ridging will provide mainly dry weather through the
weekend. A fairly tight pressure gradient across the eastern
half of the region between a developing surface low off of the
east coast and a high moving in from the west will lead to gusty
winds on Saturday, with gusts of 20 to 30 mph possible. High
temperatures will range from the low 50s across the northern and
western mountains to the low 60s in the southeast.

The next chance for rainfall will come on Monday as the ridge
begins to breakdown and a shortwave passes to our north.
Moisture is limited with this system and any rainfall will be
light. Most guidance shows another system approaching from the
west towards the middle of the week, but there is still
considerable spread in the ensembles as to how this system
evolves.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
Under the influence of high pressure building into the region,
there is very high (~100%) confidence in VFR conditions through
06Z Thursday at all airfields outside of BFD, where there still
remains high (~80%) confidence in VFR conditions. The main
uncertainty at BFD remains some fog potential in the vicinity of
BFD closer to sunrise (08-11Z Wednesday); however, the bulk of
model guidance does outline VFR conditions continuing through
the timeframe. Recent RAP model soundings do continue to outline
some low-level moisture making close approaches to the airfield
with HREF probabilities still near/below 20% of visibilities
less than 6 miles. Clear skies are virtually certain through
~22Z Wednesday with a scattered-to-broken ceiling ~25000ft AGL
expected to begin entering central Pennsylvania and progressing
eastwards throughout the evening/overnight hours. There will
also be some gusty winds at BFD/JST during the afternoon/evening
hours on Wednesday due to a tightening pressure gradient across
western Pennsylvania with wind speeds at all other airfields
expected to stay below 10kts.

Outlook...

Wed Night-Thu...Restrictions possible Wednesday
night with another frontal system/rain/LLWS.

Fri-Sat...Restrictions poss NW. Mainly VFR elsewhere.

Sun... VFR conditions likely with a few showers possible late.

&&

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

&&

$$

SYNOPSIS...Fitzgerald
NEAR TERM...Dangelo
SHORT TERM...BJT
LONG TERM...Bauco
AVIATION...Bauco/NPB