-- Discussion containing changed information from previous version are highlighted. --
227
FXUS61 KCTP 181540
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1140 AM EDT Tue Jun 18 2024

.SYNOPSIS...
*Long duration and potentially dangerous heat wave this week
*Near-record high temperatures 90+ degrees into the weekend

&&

.NEAR TERM /UNTIL 8 PM THIS EVENING/...
1050AM/1450UTC: Overall setup today looks similar to yesterday
with diurnally enhanced t-storm clusters expected to develop
within instability/pwat axis on the northwest periphery of heat
dome centered over the Mid Atlantic region. Locally strong to
potentially damaging wind gusts will be possible through the
diurnal heating cycle. "Ridge-running" storms will also be
capable of producing locally heavy rainfall with pwats up to
1.75 inches.

Previous Discussion Issued: 223 AM EDT Tue Jun 18 2024

Upper high pressure (325dam at 7H) will reside directly overhead
for today. That should help to keep a lid on things trying to
grow very tall. But, we had similar heights yesterday, and quite
a few storms got going over the nrn tier and wrn mtns. So, we
expect similar developments this aftn. The RAP (03Z run) erases
the llvl CINH by Noon-1 PM at BFD and JST (per model
soundings), but upper levels still very warm. Little shear means
they could just rain themselves out as they move little from
their initiation spots. 1.6" PWAT is nothing to sneeze at, but
the cells shouldn`t last all that long to make for a flooding
risk today. SPC has put the Allegheny Plateau into a MRGL risk
for SVR. The hot air means there is no svr hail risk, and
it makes for a cap to overcome. Without wind/shear, organization
will be poor. CAPEs get to 1500 from the RAP and GFS, and 3000
from the NAM - but only with a boost from the elevations and
interacting outflow boundaries. Seeing what happened Mon
aftn/eve, it`s probably going to be another very limited threat
for svr storms again today.

&&

.SHORT TERM /8 PM THIS EVENING THROUGH FRIDAY/...
Heat continues to be the problem/challenge in the short term
period. Wed may actually be a bit cooler than Tuesday, but we`ll
continue with the heat advy as all the forecast offices wish to
continue it/them as is. WPC has placed the NW into the Day2 ERO
with an eye toward the high PWATs and slow storm movements (much
like today). The cap from the upper high/ridge will keep
most/all of the convection to the north/east of IPT-UNV-JST Wed
and Thurs. The aftn/evening showers will probably help keep the
temps down a bit there, but the mugginess/dewpoints will likely
get enhanced by the precip. So, the Heat Advy seems like it is
solid.

Prev...
The heat and humidity are progged to build through midweek, as
the center of the subtropical high lifts north over PA. Current
guidance indicates heat indices will reach 95 to around 100F
especially in the valley locations during the afternoons Tue-
Thu. We extended the heat advisory through 8pm Thursday which
aligns well with neighboring WFOs to the west, north, and east.

Model guidance continues to favor isolated to scattered diurnal
t-storm risk Tue-Thu downwind of Lake Erie and over the higher
terrain along the spine of the Alleghenies. Thursday looks like
the hottest day of the period with maxT 90-95F or +10-20F above
climo.

Heat looks like it will continue into the weekend. Trying to
make decision on if and for how long to extend the heat advy.
Friday looks like the hottest day, and some spots could get near
105 HI on Friday in the SE. But, very few spots. At this point,
we`ll just add another day onto the area-wide heat advy, and run
it thru Friday evening.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
The heat and humidity will continue into Saturday, although we
could begin to see some slight relief working into northeastern
PA in the form of a backdoor cold front. It will be another hot
day for much of the area though, and could easily see
continuing to push the advy out into the weekend for much of the
CWA. The proximity of the cold front will bring a slight
increase in PoPs, esp across north-central and northeastern PA.

Sunday into Monday should see the (slightly) cooler temperatures
expand southward as a cold front crosses the area. This front
will be accompanied slightly increased PoPs areawide Sunday
into Monday.

Any subtle cool down early next week looks like it will be
short-lived, with heat building once again by midweek.

&&

.AVIATION /16Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --
Hazy, hot and humid conds will be the rule across central PA
for the next few days. There could be a few storms that pop up
again this afternoon with daytime heating, with the best chc
being over the higher elevations of the Allegheny Plateau. Brief
reductions and gusty winds are expected in any storms, but
these should be widely scattered. Most locations will be VFR for
the majority, if not all, of the day.

Another warm and muggy night is in store, with any lingering
showers/storms quickly diminishing as we lose the heat of the
day. Patchy fog is once again possible in areas that see
downpours today, but not confident enough to put it in any
specific TAF sites yet.

Outlook...

Wed-Sat...Predominantly VFR, with continued heat and iso TSRA.
Density altitude concerns possible.
-- End Changed Discussion --

&&

.CLIMATE...
A period of much warmer than average temperatures is expected
across much of central Pennsylvania next week, with record high
temperatures being challenged. The record high temperatures for
some sites across central PA are outlined below:

 Jun 18 Jun 19 Jun 20 Jun 21

Harrisburg      97/1957     98/1994     98/1931     98/1923
Williamsport    97/2018     96/1929     101/1923    97/1933
State College   94/1923     94/1931     94/1953     94/1988

Highest Max Temperature for June:

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 in POR since 1957)

*Harrisburg had a run of 11 days that started on 26th and ended
 on July 6th in 1901

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory until 8 PM EDT Friday for PAZ004>006-010>012-
017>019-024>028-033>037-041-042-045-046-049>053-056>059-
063>066.

&&

$$

SYNOPSIS...Steinbugl
NEAR TERM...Dangelo/Steinbugl
SHORT TERM...Dangelo
LONG TERM...Evanego/NPB
AVIATION...Martin/Evanego
CLIMATE...Steinbugl/NPB