FXUS61 KCTP 082349

Area Forecast Discussion
National Weather Service State College PA
749 PM EDT Wed Jul 8 2020

A rather stagnant mid summertime pattern continues through the
weekend with isolated to scattered afternoon and evening
thunderstorms. Some of the thunderstorms could bring locally
heavy rain and gusty winds.

The eastern third of the state could experience a larger area
of moderate to heavy rain late Friday morning through early
friday night as a sub tropical low pressure system rides north
along or just inland from the Mid Atlantic Coast.


Latest radar trends show the weakening and shrinking of storms
over the past 2 hours, especially over the west. Last few scans
show things dropping off very quickly, now. PoPs will show a
blend back to going forecast later tonight after initializing
with radar- based tweaks. Humidity will be very high through the
night with areas of fog forming, especially in places where it
has rained.

Isolated to scattered SHRA/TSRA acrs central and southern PA
this afternoon (with more numerous and heavier showers and TSRA
over the far eastern portions of the CWA) will likely see a
slight expansion of coverage late today through early this
evening as showers and TSRA that formed along the Lake Erie
breeze head south into PA from New York State, and outflow
boundaries from the current Central and Southern PA convection
enhances a convergence zone near and to the north of I-80.

Last few runs of the HRRR display this trend. Main area of
concern will still be across the Susq Valley and Western Poconos
where FFG values are only 1-1.5 inches and the heaviest rain
fell so far today (over 2 inches in parts of Schuylkill County.

A Flash Flood Watch continues through 02Z Thu for several
counties in our eastern CWA.

Late afternoon temps will be between 85 and 90F with the highest
heat indices mainly in the mid 90s throughout the central and
southern valleys.

Showers diminish quickly between 03-05Z per the HRRR and HREFV2,
leaving the remainder of the night muggy with light wind and
partly cloudy skies.

Daybreak low temps will vary from the mid 60s across the
northern and western Mtns to the low 70s in the SE metro areas.


Patchy fog and low stratus to start Thursday should give way to
a mix of sun and clouds for the bulk of the day.

Convective potential looks less based on HREFV2 and examination
of mid level temps which will be 1-2C warmer than today, which
should effectively cap deep convection outside of subtle
terrain forcing and along diff heating boundaries (near morning
cloud edges and areas that have received heavier rain the past
several days).

highest POPs 20-30% were painted across the northern tier of

High temps will be very similar to Wednesday's ranging from the
mid 80s across the higher terrain to the low 90s in the Central
and Southern Valleys. There will be no relief from the high
humidity and mugginess.


First half of the long term period will be dominated by upper
troffing developing over the northeast, by a series of shortwaves
forecast to move east through the Northern Plains and Great
Lakes, and the track of a disturbance currently off the Carolina

The coastal low will likely turn winds out of the SE and E for
later Friday and into the first part of the weekend, bringing
an increase in humidity and clouds over at least the eastern
half of the CWA. The bulk of the precip associated with the
coastal low looks to fall east of the area, areas along the
eventual track of the low will see increased pops.

The weekend looks unsettled as an upper trough digs over the
eastern US and interacts with the coastal low. Cooler temps
aloft and plenty of clouds should bring a period of relief to
the heat, with afternoon highs just a couple degrees above
average Fri-Tue.

For the second half of the period, guidance suggests that upper
heights will build to near 600 dam over PA by late next week as
the upper trof that dominated the first half of the period lifts
out. Elevated threats from heat look to spill back into our
area by Wed of next week and continue through the end of the
long term period.


Scattered showers/storms continue drift slowly southward across
central PA this evening, and may cause brief reductions in cigs
and vsby as they pass.

The overnight will be a near repeat of the past couple of
nights, with patchy fog and/or low clouds causing reductions.
Expecting widespread MVFR cigs/vsbys by daybreak, with a few
sites trending IFR for a couple of hours. Significant rainfall
earlier at JST and LNS would suggest that they may be the more
likely airfields to see fog overnight.

Expect improvement on Thursday, with conds becoming VFR as fog
burns off and the low clouds lift and dissipate. There could be
a late day shower or storm, although there should be less
convective activity than what we've seen the past couple of


Thu...Patchy AM fog/low clouds. Becoming VFR.

Fri...Reductions possible in patchy AM fog/low clouds.
Showers/storms developing (mainly SE).

Sat...Scattered showers and storms with reductions likely.

Sun-Mon...Generally VFR, although a PM shower or storm is


It looks like the streak of 90-plus days at IPT and MDT is over.
Temps Tuesday only hit 83 at IPT and 84 at MDT.

A sustained period of above-average temperatures is expected
to continue through the end of the week. A heat wave is defined
as 3 or more days with temperatures greater than or equal to 90
degrees. Here are some facts about previous heat waves from
Harrisburg (MDT) Williamsport (IPT), and State College (STC),
which have climate periods of record dating back to the late

Recent high temperatures:
7/2 7/3 7/4 7/5 7/6 7/7 90-deg streak
IPT: 95 95 91 93 94 83 5 days (over)
MDT: 93 97 94 96 97 84 5 days (over)
STC: 89 90 88 89 92 80 1 day (over)

Longest stretch of consecutive 90 degree days:
IPT: 15 (July 4 - July 18, 1988)
MDT: 11 (5 times, most recently July 22 - August 1, 1999)
STC: 15 (July 4 - July 18, 1988)

Annual occurrences of 90 degree days:
Average Most (Year) Least (Year) 2020 (thru 7/7)
IPT: 16 42(1988) 0 (1979) 6
MDT: 20 60(1966) 3 (2004) 8
STC: 8 35(1988) 0 (11 times) 3

How common are stretches of 5 or more consecutive 90 degree days?
IPT: 15 times since 2000 (12 of 20 years)
MDT: 19 times since 2000 (12 of 20 years)*
STC: 4 times since 2000 ( 4 of 20 years)

*MDT had a stretch of 10 straight 90 degree days from July 3 -
July 12, 2012. Time will tell if this year's 90 degree stretch
that began on July 2 can rival the streak 8 years ago.


Flash Flood Watch until 10 PM EDT this evening for PAZ053-058-


NEAR TERM...Lambert/Dangelo
SHORT TERM...Lambert
LONG TERM...Gartner/Colbert
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