-- Discussion containing changed information from previous version are highlighted. --
019
FXUS61 KCTP 200319
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1119 PM 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 /UNTIL 6 AM THURSDAY MORNING/...
-- Changed Discussion --
A strong thunderstorm remains possible this evening along a
weak northwestward drifting surface trough over parts of Warren,
Mckean and Elk counties where the 03Z SPC mesoanalysis shows
CAPEs near 2000J/kg and Downdraft CAPEs around 1000J/kg. Lack
of large scale forcing should cause convection to dwindle as the
boundary layer cools/stabilizes after midnight.

It will be another muggy night under a subtropical ridge parked
over the Mid Atlantic. See no reason to deviate from NBM min
temps, which are in the 65-70F range. Patchy fog is likely
late tonight in any spots across the NW Mtns that received rain
this evening. Upstream satellite imagery indicates skies will
average mostly clear overnight.
-- End Changed Discussion --

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
The upper level high that was located from Eastern PA to the
Southern New England Coast today will shift slowly southward
Thursday to a position just south of PA. The slight height falls
associated with this shift will result in a better chance for
ring of fire convection Thursday over the northern tier,
closest to a weak cold front sagging south through upstate NY.

Progged wind shear remains weak in general across Central PA
Thursday. However, slightly higher mid level flow to the north
could support a few strong to severe PM tstorms near the NY
border, where HREF UHEL values near 75 indicate the potential of
organized multicells/clusters. From I-80 southward, mid level
capping will likely suppress any convection.

Ensemble mean 850mb temps remain very similar to today,
supporting highs ranging from the upper 80s over the higher
terrain of the Alleghenies and between 90-95F in the valleys
further east. Moderate humidity with dewpoints in the mid 60s
should translate to max heat indices in the 90s.

Lack of strong large scale forcing should result in convection
over the N Mtns dying after sunset. Latest NAMNest and SREF prob
charts indicate patchy late night valley fog is likely across
the N Mtn, especially where any rain falls.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
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.
-- End Changed Discussion --

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Predominantly VFR conds were found across central PA at 03z,
outside of a SW-to-NE oriented band of SHRA/TSRA over the NW
mtns (near BFD).

Lingering shower activity over NW PA should gradually diminish
with the loss of daytime heating, leaving a warm and somewhat
muggy overnight. We could see some fog formation in the vicinity
of BFD, with the wet ground and temperatures already dipping to
near the dewpoint. Elsewhere, we could briefly see some light
fog/haze towards daybreak.

Thursday will feature predominantly VFR conds once again.
Similar to today, there could be a few late-day SHRA/TSRA across
mainly northern PA.

Outlook...

Fri-Sun...Predominantly VFR, with continued heat and iso
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 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...Fitzgerald
SHORT TERM...Fitzgerald
LONG TERM...Fitzgerald
AVIATION...Evanego
CLIMATE...Evans/Colbert