NWS Forecast Discussion
400
FXUS61 KCTP 182027
AFDCTP
Area Forecast Discussion
National Weather Service State College PA
427 PM EDT Sat Jul 18 2026
.WHAT HAS CHANGED...
* Severe Thunderstorm Watch #492 in effect until 01Z Sunday
* Expanded the Flash Flood Watch (until Midnight EDT tonight)
north to cover all of the CWA with the exception of the
Northern Tier Counties - based on this mornings MCS and
additional several rounds of storms with very heavy rainfall
rates this afternoon and evening as a warm front over the
Alleghenies moves slowly across Central PA
* 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 locally very heavy
rainfall are possible from mid-day into late this 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 through early this evening. A few
tornadoes area also possible with the strongest storms.
Little change from the previous disc regarding the severe TSRA
potential this afternoon/evening as the one-two punch of a warm
front/cold front helps to focus several rounds of convection.
Based on the number of afternoon TSRA that impacted ELK county
and adjacent parts of the northern Mtns (along with the rather
extensive coverage of ground- priming TSRA that blossomed into a
MCS this morning), we thought it would be prudent to expand the
Flood Watch (through 04Z Sunday) a layer of counties further
north.
Previous...
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/thunderstorms 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 supporting the initial rounds of mid to late
morning convection will be moving east of the Susq Valley early
this afternoon, followed by some cloud thinning and recovery
with pockets of MDT-STG Sfc-Based instability developing for the
afternoon and evening hours. This will help to ramp up the
threat for SVR TSRA and increase rainfall rates within the very
juicy airmass.
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 during the early and mid
afternoon hours.
Some of the storms 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 /20Z SATURDAY THROUGH THURSDAY/...
Aviation concerns continue to revolve around convection across
northwest and south central PA through the afternoon hours. To a
lesser extent, FU continues across the region, dropping
visibilities to MVFR and IFR.
The first area of convection will move out of the southern part
of the state by late afternoon and focus will rthen shift back
to northern PA as a cold frontal boundary sags through the
state.
Confidence is about 40% that convection and associated -SHRA
will combine with low level smoke to bring down visibilities to
LIFR for a time this evening and overnight.
Expect conditions to improve Sunday morning as the cold front
pushes out low level smoke, and convection moves south of the
area. Conditions will improve from IFR to VFR by mid morning
with the last hold outs being any locations that had dense fog
overnight.
Outlook...
Mon...Mainly VFR.
Tue-Wed...Restrictions possible in showers/t-storms with cold
FROPA expected between Tuesday/Wednesday.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
Flood Watch until midnight EDT tonight for PAZ010>012-017>019-
024>028-033>036-041-042-045-046-049>053-056>059-063>066.
&&
$$
WHAT HAS CHANGED...Lambert/Dangelo
KEY MESSAGES...Lambert/Dangelo
DISCUSSION...Lambert/Dangelo/Steinbugl
AVIATION...Tyburski
NWS CTP Office Area Forecast Discussion
