-- Discussion containing changed information from previous version are highlighted. --
713
FXUS61 KCTP 200252
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1052 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/...
A strong thunderstorm remains possible this evening along a
weak northwestward drifting surface trough over parts of Warren,
Mckean and Elk counties where the 00Z SPC mesoanalysis shows
CAPEs near 3000J/kg and Downdraft CAPEs >1000J/kg. Lack of large
scale forcing should cause convection to dwindle as the boundary
layer cools/stabilizes late this evening.

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 will be
possible late tonight in any spots across the NW Mtns that
receive rain this evening. Upstream satellite imagery indicates
skies will average mostly clear overnight.

&&

.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/...
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.

Hot early summertime temperatures will continue into this
weekend as an upper level high retrogrades west over the Ohio
and Tennessee Valleys. At the surface, the Bermuda high looks to
remain strong and anchored across the western Atlantic through
early this weekend. This will help to maintain H85 temperatures
of 20C+, resulting in heat indices topping 100F through Sunday,
particularly across south central PA into the Lower Susquehanna
Valley. Have maintained the Heat Advisory through Saturday as
Sunday still raises some questions as to exactly when the front
and associated rain will arrive.

Afternoon/evening showers and storms may become more numerous
Friday and Saturday, especially across northern PA, as heights
lower with the westward movement and weakening of the upper
ridge in combination with an approaching upper trough and
downstream energy moving along the central Canadian/CONUS
border. Areas farther south look to see showers/storms later
Sunday into Monday as the aforementioned trough dives south and
brings a cool front into the Commonwealth. This will bring a
period of drier/cooler northwest flow Monday/Tuesday, before
backing zonal flow and rising heights bring a return to more hot
and humid conditions by mid next week.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
-- Changed Discussion --
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.
-- 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 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...Guseman/Dangelo
AVIATION...Evanego
CLIMATE...Evans/Colbert