379
FXUS61 KCTP 201121
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
721 AM EDT Thu Jun 20 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 bringing brief relief from the humid
weather.

&&

.NEAR TERM /THROUGH TONIGHT/...
Forecast rolling along nicely. Dewpoints needed to be tweaked a
tiny bit as they remain below 60F in the higher elevation spots.

Prev...
The dewpoints are already a bit lower across much of the CWA
this morning. Some recovery is expected this morning to pump
everyone back into the m-u60s, and some spots (NY border) get
around 70F for Td today. Maxes are pretty much unchanged, and
have pretty much copied the MaxTs from yesterday into today.
While this will result in heat index values not quite getting to
100 in most/all places today, the Heat Advisory still looks
warranted for everyone using the logic of the past few days.

MCS moving over the Niagara escarpment early this AM has pushed
a gust front/boundary into the NW mtns. Expect this feature to
stall and stretch out over the nrn tier counties and remain in
place for the day. This could be the focus for SHRA/TSRA to pop
in mid-day. The majority of the storms will be across wrn NY
state where the heights are lowering. There will be more
organization to the storms today vs the past couple of days.
While shear is higher today, it is still fairly unimpressive.
The large CAPEs and weakening cap over the nrn tier lead to a
bit more concern for damaging gusts and marginal (1") hail -
mainly along and N of Route 6, but some stronger storms could
drop down as far S as I-80. Little/no precip is expected in the
srn half of the area, but if anyone could see a stray
shower/storm, it would pop off the highest ridges of the
Laurels. Have kept the PoPs nil there for now.

The threat for heavy rainfall is still here. Despite slightly
lower PWATs today, the storms still won`t be moving too fast.
Also, the nrn tier does have the lowest FFG numbers for the CWA
as they have been the recipients of the most rainfall lately.
The threat is not widespread enough to post a flash flood watch
at this point.

As the storms diminish tonight, fog is expected to form and
could get dense overnight. Mins hold in the 65-70F range.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
The ring-of-fire will be along the nrn tier again Friday with a
weakness in the sfc pressure over the nrn and central counties.
The heights continue to lower and this lowers the stability for
the aftn and evening even further for Fri vs Thurs. This will
allow for convection to be scattered about a wider area on Fri.
Some threat of severe wind/hail still exists. SPC has a MRGL
risk over most of the CWA. This seems warranted. But, the
similarities to Thurs may mean that the risk may be a little
higher than advertised at this point, and we could see us get
bumped up to a SLGT risk with later updates.

Temps will start out 3-5F higher on Fri AM vs Thurs and help the
SErn 2/3rds of the CWA get into the m90s or better. The higher
Td on Fri will give us just enough of a boost to have more
places get at or above 100 heat index.

The storms should diminish from W-E Fri night. Since more
places should receive rainfall Fri and early Fri night and some
clearing is expected behind the storms, we should get a more-
widespread fog to form.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Medium range guidance indicates PA will remain under a low
amplitude upper level ridge through the upcoming weekend with a
strong surface high parked near Bermuda, resulting in a
continuation of the heat and humidity. Ring of fire convection
looks likely Friday and Saturday, especially along the northern
tier of the state, closest a stalled front near the PA/NY
border. Model 0-6km shear remains weak Friday, but a slight
increase in mid level flow could result in a better chance of
organized severe wx over Northern PA Saturday PM.

Current 2m and 850mb temps plumes indicate some of the hottest
weather of this heat wave will occur between Friday and Sunday,
so may need to extend the heat advisory, which currently only
lasts through Saturday. Mean EPS 850 temps peak near 22C across
Southern PA late in the weekend, supportive of max temps near
100F across the Lower Susq Valley.

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 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.

&&

.AVIATION /11Z THURSDAY THROUGH MONDAY/...
Patchy fog across the northern tier will dissipate quickly over
the next hour or two. Once this happens, VFR conditions are
expected areawide for most of the day. All guidance shows
thunderstorms developing near the New York border during the
late afternoon/early evening, but there are differences in the
models with respect to how far south the storms reach. At this
point, BFD appears to be the most likely airfield to be
impacted. Brief visibility reductions will be possible in any
thunderstorms, along with the potential for strong winds.

Model soundings support fog development overnight across the
north and the HREF shows greater than 50% probabilities of
visibilites dropping below 1/2 mile after 06Z at BFD.

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.

&&

.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 on
  Tuesday Jun 18, which tied the old record of 92 degrees set
  back in 1994.
* A record high temperature of 90 degrees was set at Bradford on
  Tuesday Jun 18. This broke the e old record of 87 degrees set
  back in 1993.

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.

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

     ............ Jun 20 .... Jun 21 .... Jun 22 ..

Harrisburg      98/1931     98/1923     nn/YYYY
Williamsport   101/1923     97/1933     nn/YYYY
State College   94/1953     94/1988     nn/YYYY

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...Dangelo
SHORT TERM...Dangelo
LONG TERM...Fitzgerald
AVIATION...Bauco
CLIMATE...Evans/Colbert