847
FXUS61 KCTP 211914
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
314 PM EDT Fri Jun 21 2024

.SYNOPSIS...
Heat will peak this weekend and isolated to scattered
thunderstorms will occur late today and again Saturday
afternoon and evening.

The showers and storms will be more numerous on Sunday as a
cold front pushes into the Commonwealth and gusty winds along
with heavy rain may accompany these slow moving storms.

Some relief from the heat and humidity expected Monday

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
It`s been 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.

The lack of significant llvl convergence, vertical mixing of
drier air/sfc dewpoints dipping by several deg F into the mid
60s and a distinct north/south axis of 300 mb convergence from
near KBFD to KAOO has kept TCU limited and any TSRA very
brief/pulsy so far today.

The best upper level divergence, but generally weak westerly
deep layer shear, will reside along the PA/NYS border for the
rest of the afternoon/evening.

Small, narrow-looping hodographs point to slow storm motion
once again and perhaps some better storm relative inflow and
slow SE movement to the storms through the moisture rich
environment with PWAT Values around 1.5 inches. Lower PWAT air
of around 1.25 inches and nearly cloud free skies were noted
across the Susq Valley and Western Poconos.

Equil Levels of around 40 KFT in these quasi pulse storms
should support some localized wet microbursts and 1-1.5 inch
hail.

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 measurable 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 /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Expect the low to mid level west to southwesterly flow to
freshen over the upcoming weekend which will accentuate the
already high temperatures/hot conditions with some
downslope/adiabatic warming of the air.

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 /SUNDAY THROUGH FRIDAY/...
Upper ridge continue to flatten Saturday night and Sunday with
the warmest overnight temperatures of this heat episode
expected into Sunday morning. A round of showers/tsra will
accompany this flattening as a cold front crosses central PA
Sunday afternoon through Monday morning, but one more day of
dangerous heat is expected over the southeast third of central
PA Sunday afternoon with heat indices approaching or exceeding
100F. We`ll be extending the Heat Advisory through Sunday
evening for the Lower Susq River Valley as a result.

Behind the cold front, we expect still warm but much less humid
conditions to arrive by Monday and last into Tuesday, as
dewpoints drop into the 50s. This temporary relief from the heat
will give way to another surge of heat and humidity for late
Tuesday through Wednesday before a more refreshing air mass
arrives for Thursday and Friday of next week.

&&

.AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
Widespread VFR will continue for the rest of today and this
evening. Isolated to scattered, pulse showers and thunderstorms
will be found across the NW two thirds of the CWA through about
01Z before a sharp dropoff in POP occurs.

Patchy fog will develop overnight into early Sat 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>027-033>035-037-041-042-045-046.
Heat Advisory until 8 PM EDT Sunday for PAZ028-036-049>053-
056>059-063>066.

&&

$$

SYNOPSIS...Lambert
NEAR TERM...Lambert
SHORT TERM...Lambert
LONG TERM...DeVoir
AVIATION...Lambert/Bauco
CLIMATE...Evans/Steinbugl/Colbert