469
FXUS61 KCTP 180727
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
327 AM EDT Sat Jul 18 2026

.WHAT HAS CHANGED...
* Tornado risk is still 5% chc of a tornado w/in 25 miles of a
  point), but the conditional intensity group 1 has been
  introduced S & E of Harrisburg
* Damaging wind gust threat is high (45% chc of wind damage w/in
  25 miles of any point) over almost all of the CWA

&&

.KEY MESSAGES...

1) Severe thunderstorms with damaging winds and heavy rainfall
are possible from mid-day into late evening. Tornadoes also
possible.

2) Sunday & Monday quiet but Tues looks active again with
severe and flood risks returning.

&&

.DISCUSSION...
KEY MESSAGE 1: Severe thunderstorms with damaging winds and
heavy rainfall are possible from mid-day into late evening.
Tornadoes also possible.

SPC has kept the Enhanced risk of severe weather expectation for
all of Central PA today. They have also added a special
(conditional intensity group or CIG) hatching to SErn PA
(including areas S & E of Harrisburg. The CIG designation means
that tornadoes that do develop in that area could be stronger
than just EF0/1. A reasonable maximum intensity of EF2-strength
tornadoes is possible today - again, mainly in SE PA.

Early showers and even a thunderstorm or two will occur
near/along a pair of warm fronts moving north and east through
the area this morning and early afternoon. The vort max moving
into western PA at 07Z is expected to continue to touch off
showers this morning. Some lightning is possible, mainly across
the S. There should not be a threat for severe weather until at
least late this morning after we can get the clouds and showers
away and get some heating/pump up the CAPE.

The timing of that vort max and the SHRA/TSRA it helps generate
look like they will be early enough in the day that ample
heating should then occur as the main warm front pushes into
the srn counties and across the CWA late this morning and early
this afternoon. As the CAPEs climb, and the wind
profiles/hodographs become rounded, the risk for deep
convection that would also take advantage of the high helicity
to produce supercells increases. This convection could start a
couple hours earlier than climatologically-favored timing...more
like a noon kickoff than early- to mid-aftn. The risk for
discrete, spinning cells is highest over the Lower Susq, but is
possible anywhere across the CWA with the warm front(s) and
varied boundaries from earlier rain and differential heating
playing roles to make the near storm llvl/blyr environment
favorable. 70F+ dewpoints will arrive in the S with the first
warm front, and the LCLs should be low and favorable for tornado
development. The Sig Tor Parameter (STP) is highest over the
SE, esp in Lancaster Co. Lower (l-m60s) dewpoints hang on
across the N for much of the day.

The NW will have the next-best chance for severe storms to
develop. However, the increasing moisture and moderate-high
shear and moderate-high CAPEs will mean we`ll have to watch all
of the CWA for storm initiation in early and mid afternoon.
These could also be supercells away from the SE - at least early
in the event. The wind profile becomes more-aligned/straight
hodographs that would be more favorable for storm clusters or a
broken line, esp if a pre-frontal trough materializes.

The cold front moving down from the NW should arrive late in
the day and could continue to provide lift for storms in the NW
half of the area into the evening. But, it may arrive in most
places too late (after stabilization from other/earlier precip)
to make a wide threat for severe wx to occur along it as it
passes. Expect precip along the cold front to weaken and fall
apart the deeper it gets into the CWA (into the central mtns).

If there is a chance for a bust or weakness in the severe
forecast it is over the central mtns/ridge-and-valley region.
Potent storms are likely/certain in the SE and the NW, but are
less certain in the Laurels and ridge and valley counties.

  ----------------------------------------------------------

KEY MESSAGE 2: Sunday & Monday quiet but Tues looks active again
with severe and flood risks returning.

A drying trend is expected Sunday with noticeably lower
humidity allowing for a pleasant day and relatively cool night.
However, latest RRFS shows some near sfc smoke returning to CPA
from the Great Lakes. This could result in reduced air quality
and hazy sky conditions.

Additional bouts of rain/t-storms are possible into the
workweek. The first of which will be around Tuesday (Day4) as a
well-developed synoptic storm moves through the Great Lakes and
NE CONUS. SPC has been highlighting a 15% prob (equivalent to
SLGT risk, level 2/5) for Central PA. Forcing/support for this
medium range severe outlook appears fairly robust and would take
stock in this risk manifesting at shorter ranges. WPC is also
highlighting Tuesday for heavy rainfall and possible flooding
with the synoptic system generating multiple chances for rain
with high atmos moisture in place.

Temperatures will trend near to slightly below historical
averages through late week into month-end with some noticeably
cooler nights possible.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
There will be two major areas of concern for the next 24 hours.
The first will be the continued visibility restrictions at all
terminals due to heavy surface smoke concentrations.
Visibilities will continue to remain less than 6 miles across
most of the Commonwealth through the early morning hours.
Anticipate widespread IFR and MVFR restrictions until after 16Z
Saturday. A surface center of low pressure is expected to move
over the Mid- Atlantic region today, and this will usher out the
smoke this afternoon while also bringing convection to the
region.

The timing of this convection remains the second point of
concern. The consensus thinking is there will be two rounds of
storms today. The first will come this morning as a cluster of
showers will develop along the leading moisture edge ahead of
the front (PWATs increasing to 1.5"-2.0") as moisture filters
in ahead of the Great Lakes system, with a few thunderstorms
being possible as this activity progresses west to east across
the Commonwealth. This activity should largely end from west to
east between 16 and 18Z. The second round of storms will kick
off later in the afternoon with a main line of storms along the
front developing between 20 and 22Z. Convection is expected to
exit the southeastern terminals of KLNS and KMDT by 06Z Sunday.
These storms today will be strong to severe and may produce
gusty winds, heavy rain, and flight restrictions.

Outlook...

Sun...Lingering -SHRA with restrictions possible early (primarily
driven by low ceilings), with VFR favored otherwise.

Mon...Mainly VFR.

Tue-Wed...Restrictions possible in showers/t-storms with cold
FROPA expected between Tuesday/Wednesday.

&&

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

&&

$$

WHAT HAS CHANGED...Dangelo
KEY MESSAGES...Dangelo
DISCUSSION...Dangelo/Steinbugl
AVIATION...Bowen