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849
FXUS61 KCTP 210132
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
932 PM EDT Thu Jun 20 2024

.SYNOPSIS...
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* Heat and humidity will continue to build through the weekend
  as temperatures exceed 90F and heat index values approach
  100F.
* Scattered daily afternoon showers and thunderstorms may
  produce locally heavy rainfall and gusty winds, especially
  Friday afternoon.
* A cold front moving through the region Sunday night into
  Monday will bring a brief break from the persistent heat
  early next week.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH FRIDAY/...
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Thunderstorms and heavy rain across northern PA have tapered off
this evening with the loss of daytime heating. Radar estimates
indicate as much as 4 inches of rain fell across parts of Potter
County this afternoon, though no significant impacts were
reported today. Today`s rainfall, which was focused primarily
along and north of US-6, may set the table for more impacts
tomorrow if storms end up tracking over already-saturated
locations.

Clear skies will persist tonight with calm winds under a dome of
high pressure. Fog is expected to form across the north and
could get locally dense for a few to several hours late
tonight/early Friday. Mins hold in the 65-70F range.

On Friday, the mid/upper level high will retrograde south and
west into the south central US, resulting in flow across
Northern PA becoming increasingly diffluent above the main axis
of high PWAT air. This pattern is conducive to a ring- of- fire
pattern with convective clusters developing across a larger
area with more notable East or ESE progression than we`ve seen
in recent days. In addition, deep layer (0-3KM) shear will
increase to around 20 kts across the Northern Mtns Friday
afternoon and evening, providing additional support for
organization.

SPC has a MRGL risk over most of the CWA, but the risk may be a
little higher than advertised at this point, and we could see
us get bumped up to a SLGT risk (at least across the Northern
half of PA) with later updates. A MRGL risk of Excessive
Rainfall is in place along and north of I-80 where recent rains
have dropped flash flood guidance to an attainable level. Still
only expect isolated issues, given the scattered and progressive
nature of expected thunderstorms.

Temps will start out 3-5F higher on Fri AM vs Thurs and help
locations along and southeast of the Allegheny Front get into
the mid 90s Friday afternoon. The higher dewpoint will also
support heat index values approaching 100F Friday afternoon.
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&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
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The storms should diminish from W-E Fri night. Since more
places should receive rainfall Friday and early Friday night
and some clearing is expected behind the storms, we should get a
more- widespread fog to form, especially in the deeper valleys
of northern PA and in the Susquehanna Valley. Latest HREF progs
these areas with the highest probability of fog formation.

Heat builds to a crescendo Saturday through Sunday with daytime
heat indices likely to eclipse 100F both days over the far
south and southeast, and nighttime lows peaking Sat
night/Sunday morning in the mid to upper 70s in these areas. In
the midst of the ongoing Heat Advisory, it is worth noting that
the experimental HeatRisk product paints the highest risk levels
of the week occurring on Saturday and Sunday. If you have plans
to do anything outside, plan to drink plenty of water and have
options for getting relief from the heat.

The ring of fire convection still looks likely Saturday and
Sunday as the upper ridge flattens, especially along the
northern tier of the state. The chance for organized severe may
increase over northern PA on Saturday with increasing bulk
shear, but only a general thunderstorm risk is in place at this
point. At some point, a heat advisory for Day 4 (Sunday) will
need to be extended for the southeast half of central PA, but
confidence is still low enough in northwestward extent of the
heat to preclude an extension of the existing advisory.
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&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
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Most locations should see a round of showers/tsra Sunday PM
into Monday AM associated with the flattening of the upper ridge
and passage of a shortwave trough and cold front. Behind this
feature, expect a return to fair and more seasonable conditions
early next week. A surge of warmer weather currently looks
likely midweek ahead of an upstream cold front, which could also
be accompanied by our next round of showers/tsra. A more
refreshing air mass is being teased for Thu/Fri of next week in
the medium range, something we would welcome at that time.
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&&

.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
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VFR conditions are expected across the bulk of the area for
tonight and most of the day tomorrow. Model soundings support
fog development overnight across the north and the HREF shows
greater than 50% probabilities of visibilities dropping below
1/2 mile after 06Z at BFD. Have included restrictions there
until 12Z.

During the day tomorrow, expect light westerly winds and the
development of scattered thunderstorms across much of the
region. The coverage of storms may be a bit more widespread than
they were today and the risk area will certainly extend farther
south than it has the past few days. VFR will prevail outside of
thunderstorms, under which brief periods of heavy rain, reduced
visibility, and lightning are likely.

Outlook...

Fri-Sun...Predominantly VFR, with continued heat and isold
aftn/eve SHRA/TSRA. Density altitude concerns possible.

Mon...Predominantly VFR, with brief reductions possible in
scattered SHRA/TSRA as a cold front crosses the area.

Tues...VFR, no sig wx expected.
-- End Changed Discussion --

&&

.CLIMATE...
A period of warmer than average temperatures is expected across
much of central Pennsylvania through the end of the week, with
record high temperatures at multiple cities being challenged
every day through Saturday.

One record was set on Thursday:
*
* A record high temperature of 90 degrees was set at Bradford on
  Thursday Jun 20th. breaking the old record of 88 degrees set in
  2012.

One record was set on Wednesday:

* A record high temperature of 88 degrees was set at Bradford on
  Wednesday Jun 19, breaking the old record of 87 degrees set in
  1987.

Highest Max Temperatures for Central Pennsylvania Observing
sites for June (date of occurrence is in parentheses:

State College 96 in 1952 (26th) and 1933 (29th)
Harrisburg 100 in 1966 (27th), 1952 (26th), and 1934 (29th)
Williamsport 104 in 1925 (5th)
Altoona 97 in 1971 (28th) and 1953 (21st)
Bradford 93 in 2022 (22nd)

Longest run of consecutive days with max temp >=90 in June:

State College 6 (24-29th 1966)
Harrisburg 10* (19-28th 1943)
Williamsport 9 (18-26th 1923)
Altoona 8 (13-20th 1994)
Bradford 0 (has not occurred since POR started at site in 1957)

*Harrisburg had a run of 11 days with temperatures greater than
 90 degrees that started on 26th and ended on July 6th in 1901.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT Saturday for PAZ004>006-010>012-
017>019-024>028-033>037-041-042-045-046-049>053-056>059-
063>066.

&&

$$

SYNOPSIS...Banghoff
NEAR TERM...Banghoff
SHORT TERM...Banghoff
LONG TERM...DeVoir/Fitzgerald
AVIATION...Banghoff
CLIMATE...Evans/Colbert