712
FXUS61 KCTP 211117
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
717 AM EDT Fri Jun 21 2024

.SYNOPSIS...
* Ongoing heat wave will peak/crescendo today through Sunday
* Gusty thunderstorm winds and locally heavy rain possible
  during the afternoon/evening today through Sunday
* Some relief from the heat and humidity expected Monday

&&

.NEAR TERM /THROUGH TONIGHT/...
Patchy dense fog over the northern tier (where it rained
yesterday) will dissipate quickly/shortly after sunrise this
morning.

Another hot and humid [first full day of summer] day across
central PA with max temps in the 85-95F degree range (near
record highs or +10-15F above the historical average - see
climate section for records)

Combination of heat and humidity will push heat index values
into the 95-100F range with some valley locations downwind of
the Alleghenies eclipsing the century mark. A heat advisory
remains in effect.

Strong boundary layer heating of moist summertime airmass will
once again promote isolated to scattered convection by peak
heating. SPC has maintained a MRGL severe t-storm risk (level
1/5) for all of central PA with gusty winds the primary concern
with the most robust updrafts. Weak shear remains a limiting
factor for more organized storms/higher categorical risk SWO.

WPC shifted the MRGL risk of excessive rain area to only include
the far northeast zones (Endless Mtns north of KIPT) which fits
the latest HREF PMM and 3-hr neighborhood probability (NP) >1"
and >3" axes. Any t-storm will be capable of locally heavy
downpours and high rain rates given sufficient CAPE and PWAT
values around 1.5 inches. Cell motions should also be rather
slow moving. Highest short duration flood risk would be across
the northern tier where FFG is lowest and HREF LPMM shows spot
amounts between 2-3 inches. Farther to the south, the ongoing
hot spell and little to no rainfall are drying topsoils out
fairly quickly and have ramped FFG much higher over the last
week; D0 drought now showing up in parts of south central PA.
Harrisburg (KMDT) has only 1 day of measureable rainfall so far
this month! (1.40" back on the 5th)

Storms should decrease in coverage and intensity by later this
evening as they track slowly to the east/southeast. Partly
cloudy to mainly clear and humid overnight with areas of fog
particularly where it rains. Latest HREF shows the highest
probability of locally dense fog over the northern tier into the
middle Susquehanna Valley. Min temps in the 65-75F range are
+10-20F above climo and provide little relief from the heat.

Following the earliest summer solstice (yesterday) in 228 years,
the first full day of summer will end with the first full moon
of the season; look to the southeast to see the Strawberry Moon
rise around 9:05pm tonight.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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.

As the upper ridge breaks down and deep layer shear values
trend higher, a more organized severe t-storm threat may develop
this weekend. SPC has introduced MRGL risk outlooks for both
Saturday and Sunday. Speaking anecdotally from ~20 years
experience, prolonged periods of heat in CPA are often broken by
at least a semi-organized convective t-storm event. That being
said, we could envision a higher SWO risk level in the cards.

The heat advisory continues through Saturday and will need to
be extended for the southeast half of central PA on Sunday.
It`s possible local heat indices could reach warning criteria
~105F in parts of the middle and lower Susquehanna Valley this
weekend and will message that in the updated NPW and DSS
briefing.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
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. The latest EPS
and GEFS both currently support fair weather with near to
slightly below normal temps and low humidity late next week, as
Canadian High Pressure builds southeast into the region.

&&

.AVIATION /11Z FRIDAY THROUGH TUESDAY/...
Valley fog is still visible on satellite this morning but
visibilities have improved to VFR at BFD as of 11Z. Scattered
thunderstorms will develop this afternoon and could lead to
brief restrictions, but VFR conditions will prevail otherwise.
The thunderstorms will be more widespread today than they have
the past few days.

Patchy fog will develop overnight in areas that see rain today.
BFD will once again be the most likely airfield to see IFR or
lower visibilities, though the HREF shows low probabilities of
fog forming as far south as UNV.

Outlook...

Sat-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.

&&

.CLIMATE...
A heat wave will continue through the weekend with near-record
high temperatures forecast in some locations Friday-Sunday.

Daily record highs for Friday June 21 to Sunday June 23:

6/216/226/23
State College 94 (1988)93 (1988)91 (1966)
Harrisburg 98 (1923)97 (1988)97 (1965)
Williamsport97 (1933) 97 (1988)94 (1923)
Altoona 97 (1953)91 (2022)90 (1994)
Bradford 89 (2022)93 (2022)86 (2013)

One record was set on Thursday 6/20:

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

One record was set on Wednesday 6/19:

* A record high temperature of 88 degrees was set at Bradford on
  Wednesday June 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)   /current streak=0/
Harrisburg 10* (19-28th 1943) /current streak=4/
Williamsport 9 (18-26th 1923)   /current streak=4/
Altoona 8 (13-20th 1994)   /current streak=4/
Bradford 0                  /current streak=1/
(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...Steinbugl
SHORT TERM...Steinbugl/Banghoff
LONG TERM...Fitzgerald
AVIATION...Bauco
CLIMATE...Evans/Steinbugl/Colbert