-- Discussion containing changed information from previous version are highlighted. --
824
FXUS61 KCTP 191515
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1115 AM EDT Wed Jun 19 2024

.SYNOPSIS...
The center of a subtropical upper level high over Pennsylvania
will sink southward over the next few days. A weak cold front
will approach and stall out over the region Friday and
Saturday. A more significant cold front is likely to push
through Sunday night or early Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
11 AM EDT Update:

Forecast pretty much on track with some minor adjustments to
clouds and a slight upward adjustment to POPs over the far NW
zones based on high res ensembles and their members that
indicate a fairly high probability for SHRA/Sctd TSRA forming
after 19Z. This part of our CWA will also be within an area of
weak mesoscale UVVEL linked to the thermally direct cell of a
weak mid/upr level shortwave lifting NE across the Lower Glakes
and along the axis of highest PWAT air of around 2.00 inches.
Will have to keep a close eye on the potential for some strong
to potentially SVR and training cells on an axis from near KGKJ
to KJHW and KOLE. Locations along this axis have 1 hour Flash
Flood Guidance values reduced to between 1.25 and 1.5 inches
from Tuesday evening`s TSRA and will be susceptible to flash
flooding from any training cells.

Pertinent parts of the previous discussion follow.

The lack of nighttime cooling/recovery and high daytime temps
continue to warrant a heat advy even if we stay just below 100F
today. The duration (many days) of the heat wave weighs heavily
in the WWA decisions, too. High clouds today will be thickest
over the west. They will make little difference in max temps
today as the 8H temps will be higher in the NW than SE. The
deepest mixing today will be a rather homogeneous 5kft across
the CWA. That puts maxes in the u80s on the ridge tops and l90s
in the valleys - very close to Tues.

Convection will build again in the middle of the day, but the
storms will be more over the nrn tier due to the upper heights
and capping being better over the srn half of the area. PWATs
remain high (>1.5") across the N, so heavy rain is possible out
of any of those storms. Pulse storms with little motion are
likely to be the mode today with the hodograph looking more like
an ink blot than a smooth line or curve. As with yesterday,
CAPE could get >2000J/kg in the nrn tier, and that could make a
wet microburst out of an isolated cell or two.

Expect tonight to be another muggy one with convection dying
down before midnight. We`ll leave a small PoP across the north
after midnight as the ring of fire flattens out and any
transitory cells could travel along the lakeshore and into wrn
NY. Mins of 65-70F will be a little lower than recent days
because some subsidence under the big upper high could inch
dewpoints down into the lower 60s in spots overnight. The
higher dewpoints will be stubborn over the nrn tier due to
earlier rainfall.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
Heights fall slightly across the nrn tier as the big high aloft
slides a little to the south. That could allow the daily pop-up
storms to grow a little taller and have a higher potential for
making wind damage. SPC Day2 puts areas N of I-80 into the MRGL
risk and far NE (Tioga/Sullivan Cos) into the SLGT risk
category. Capping should keep things less active across srn PA
on Thurs. Persistence will be the best forecast for maxes, and
the dewpoints seem to recover just fine from any lowered numbers
in the morning, getting back into the u60s almost everywhere and
around 70F in the N for the middle of the day.

Heights lower just a little more on Friday, and a weakness in
the sfc pressure field develops over the nrn tier. How far S
the weak/diffuse front will make it on Fri will help determine
the eventual coverage of storms. Will go with a 40-50pct
coverage over the nrn half of the CWA in the aftn and evening
Fri. Again, one or two of these storms could produce a damaging
wind gust. There should be a little bit of movement (W-E) to
the storms on Thursday and a little bit more on Friday. But, the
shear is still pretty weak.

Again, we`ll hold onto the heat advy for both Thurs and Friday.
Friday does look a little more muggy and the heat index values
will be a couple of degrees higher than Thursday (and Wed).

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Did go ahead and stretch the heat advisory out into Saturday for
everyone. Latest heat index fcst nums look 2-3F higher Sat than
Fri. Passed on extending it into Sunday, since the NW looks to
be a little cooler/lower (HIs in the 80s) on Sunday. The SE
half looks like they`ll get back near 100 HI again on Sunday.

Prev...
Medium range guidance indicates PA will remain under a low
amplitude upper level ridge with a strong surface high parked
near Bermuda, resulting in a continuation of the heat and
humidity. Ring of fire convection looks likely Saturday,
especially along the northern tier of the state. Falling heights
ahead of an upstream trough over the Grt Lks is likely to
result in at least scattered PM convection Sunday.

Current 2m and 850mb temps plumes indicate some of the hottest
weather of this stretch could occur next weekend, so may need to
extend the heat advisory, which currently only lasts through
Friday.

Most locations should see a round of showers/tsra Sunday PM into
Monday AM associated with the passage of the shortwave trough
and attendant cold front. Behind this feature, expect a return
to fair and more seasonable conditions later Monday into
Tuesday, as surface ridging and drier air works in from the Grt
Lks.

&&

.AVIATION /15Z WEDNESDAY THROUGH SUNDAY/...
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The highest chance of a shower or storm will be a bit further
north and west today, mainly at BFD and points west where the
axis of deepest moisture resides and some larger scale lift will
be provided by a weak upper level disturbance moving NE across
Lake Erie.

Dewpoints expected to drop off a bit today, which supports
the lower chance of showers and storms later today.

There could be some fog late tonight, mainly near BFD, but
that depends if it rains there later this afternoon.

Not much change for tonight right into Friday.

There could be a strong storm Thursday into Friday, mainly
across the northern portion of central PA, as the front sags to
the south.

Outlook...

Thu-Sun...Predominantly VFR, with continued heat and iso TSRA.
Density altitude concerns possible.
-- 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.

Two records were either set or tied for sites on Tuesday:
* A record high temperature of 92 degrees was set at Altoona
  yesterday, which tied the old record of 92 degrees set back
  in 1994.
* A record high temperature of 90 degrees was set at Bradford
  yesterday. This broke the e old record of 87 degrees set back
  in 1993.

The record high temperatures for some sites across
central PA that could be challenged are outlined below:

 Jun 19 Jun 20 Jun 21

Harrisburg      98/1994     98/1931     98/1923
Williamsport    96/1929     101/1923    97/1933
State College   94/1931     94/1953     94/1988

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...Lambert/Dangelo
NEAR TERM...Lambert/Dangelo
SHORT TERM...Lambert/Dangelo
LONG TERM...Fitzgerald/Dangelo
AVIATION...Lambert/Martin
CLIMATE...Evans/Martin