747
FXUS61 KCTP 140301
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1101 PM EDT Sat Jul 13 2024

.SYNOPSIS...
- Another heat surge/significant heat wave is expected Sunday
  through Wednesday with max heat index values reaching 100-110
  over parts of south-central PA and the Susquehanna Valley.
- An isolated late afternoon or early evening thunderstorm
  can`t be ruled out; however, most places are expected to stay
  dry this weekend.
- There is some potential for more organized/severe
  thunderstorms Monday through Wednesday.

&&

.NEAR TERM /UNTIL 8 AM SUNDAY MORNING/...
A passage of a weak surface trough has allowed for isolated
showers and thunderstorms this afternoon and into the evening
hours. The strongest complex remains across western Clinton
County as of 9pm EDT, with some promise towards SPS but pulsing
nature in an environment that is not the most conducive for
severe wx has kept these at bay for the time being. Some storms
across southern PA where additional moisture is present will
allow for lingering convection for the next couple of hours, but
generally expect mentions to diminish slightly after 11pm EDT
with the loss of daytime heating.

Muggy conditions with clearing skies are expected overnight with
MinTs running in the lower 70s across the LSQ with some
potential for lower 60s across the Laurels and N PA. There
remains some potential for radiational fog in areas that
received rainfall this afternoon/evening with model soundings
outlining some low-level moisture overnight. This is supported
with lower dewpoint depressions across N and SE PA, thus have
continued fog mentions for these areas at this time. Expansion
of fog formation remains possible across the southern tier as
showers continue this evening.

&&

.SHORT TERM /8 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
Surface ridging with dry mid-level air across central PA will
allow for a warm-to-hot day on Sunday, with heat index values
across the LSQ pushing towards and upwards of 100F and a Heat
Advisory (see NPWCTP) has been issued. The biggest uncertainty
with regards to heat index values will be mid-level dry air, if
this is able to mix down heat index values will have some
potential to underperform Sunday afternoon. It is of note that
surging moisture ahead of weak shortwave during the afternoon
and evening hours will provide another chance for scattered
convection and could inhibit drier air from mixing down. At
this time, guidance indicates the best moisture and lift will be
stationed across the Susquehanna Valley along with another area
across NW PA, thus have limited mentions to this area at this
time. Have capped PoPs in the SChc category for a majority of
the day, with thunderstorm mentions in the forecast due to ample
instability.

A stalled boundary stationed across the Great Lakes will
continue to promote SChc/Chc PoPs across NW PA through Sunday
evening with chances of precipitation confined west of the
Allegheny Front, closest to the area of best forcing. Cloud
cover across N/W PA will provide fairly uniform MinTs Sunday
night into Monday morning, ranging from the mid-to-upper 60s to
the lower 70s across the LSQ.

Confidence in excessive heat risk is higher on Monday, and has
lead to the issuance of a Heat Advisory (see NPWCTP) for the
south-central Alleghenies and Middle Susquehanna Valley on
Monday. The interaction of a modest shortwave trough, coupled
with a very warm and humid airmass is currently expected to
trigger thunderstorms Monday afternoon into the evening hours
with a slightly higher severe threat than over the weekend with
shear being be the biggest limiting factor.

Precipitation becomes more limited to NW PA overnight Monday and
into Tuesday morning. The more important sensible weather
overnight into Tuesday will be the lack of reprieve from warm
temperatures with MinTs ranging in the upper 60s (N PA) to the
mid-to-lower 70s (LSQ) with muggy conditions.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
A hot and humid airmass will be across the area on Tuesday.
Held onto current high temperatures for Tuesday, given that
the thickness is quite high. Some concern for any days up
to Wednesday could see showers and storms, given that weak
shortwaves track just to our north, around a rather large
500 mb upper level low for mid July. Main chance for storms
would be from about route 6 northward.

For later Wednesday, a cold front moves across central
Pennsylvania. Expect widespread showers and storms across
the area, as the cold front drops southeast across the region.

Wavy front just to the south and east of the Keystone state
on Thursday could still result in a shower or storm, mainly
across the southeast.

After this, high pressue builds into the area, resulting in
less humid weather, with mainly dry conditions.

Still some hints that slightly higher dewpoint air could work
back into the area by late in the weekend, resulting in a small
chance of showers.

More information below on the heat for Tuesday.

Heat pattern ramps up and peaks early next week as a large
Bermuda high pumps increasingly hot and very humid air into CPA.
850mb temps rising to around 22C supports highs peaking between
90-100F with max heat indices 100-110F. High confidence in
excessive heat risk lead to the issuance of a heat advisory for
the south central Alleghenies and middle Susquehanna Valley on
Tue and xheat watch for the lower Susq where max heat index
could reach 105-110F.

Heat index values will likely push 100F or advy criteria over
the Lower Susq Valley Wednesday afternoon.

&&

.AVIATION /03Z SUNDAY THROUGH THURSDAY/...
Scattered SHRA/TSRA this evening will continue until 03Z-04Z
before tapering off, with TSRA mentions limited in the 00Z TAF
package. Expect clouds to clear overnight with winds becoming
light, and even calm across some portions of central PA. This
will allow for some fog formation to occur across N and SE PA
overnight where dewpoint depressions are the lowest and
increased low-level moisture noted on model soundings.

The main airfields of concern overnight will be BFD, UNV, and
IPT where rainfall is most likely to occur in the 00Z-04Z
timeframe, thus have outlined these restrictions in the 00Z TAF
package. There is still some uncertainty, especially at UNV
where there is low (30%) chance of fog development and have
opted for TEMPO IFR restrictions given the lower confidence at
this time. There is increasing confidence at IPT overnight, but
will low-to-moderate confidence (30-40%) based on where TSRA
tracks this evening and how much moisture makes it into the
airfield, thus have capped at IFR restrictions with VCFG
mentions. There is higher confidence at BFD, thus have begun to
outline LIFR/IFR restrictions in the 06Z-11Z timeframe with
moderate (50%) confidence at this time.

Light winds with SKC is expected to prevail after sunrise, with
scattered SHRA/TSRA during the afternoon and evening hours. At
this time, there is too much uncertainty to even think about
adding SHRA/TSRA mentions at the airfields; however, would
promote increase caution with respect to MDT/LNS/IPT along with
potentially BFD where chances are slightly higher given
increased moisture, lift, and instability.

Outlook...
Mon-Tue...Scattered SHRA/TSRA possible areawide.

Wed...SHRA/TSRA more widespread with restrictions possible.

Thu...SHRA/TSRA chances decrease west-to-east later in the
afternoon/evening.

&&

.CLIMATE...
RECORD TEMPERATURE - A record high temperature of 86 degrees
was set today at Bradford, PA. This ties the old record which
was set back in 1979.

The duration of warm nights is noteworthy -- Harrisburg has not
dropped below 70 degrees since July 3rd. Here are the longest
stretches with temperatures at or above 70 on record at Harrisburg.

# OF DAYS   DATES      YEAR
17        7/19-8/04    2020
13        8/16-8/28    2021
13        7/13-7/25    2010
12        7/18-7/29    2022
12        7/17-7/28    1999
12        7/20-7/31    1940
11        8/04-8/14    1977
10        8/10-8/19    2016
10        7/14-7/23    2013
10        8/01-8/10    1968
10        7/21-7/30    1898
9         12 times, most recently 7/3-7/11/2020
8         7/04-7/12    2024
     .................................................

The minimum temp dipped to 68F yesterday morning (7/12) and
therefore ends the streak at 8 consecutive days. Tonight will
start another run of lows >=70F which should last until next
Thursday night (7/18 or morning of 7/19).

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from noon Monday to 8 PM EDT Tuesday for PAZ019-
025>028-034-035-045-046-049>053-058.
Heat Advisory from noon Sunday to noon EDT Monday for PAZ036-
056-057-059-063>066.
Excessive Heat Watch from Monday afternoon through Tuesday
evening for PAZ036-056-057-059-063>066.

&&

$$

SYNOPSIS...NPB
NEAR TERM...NPB
SHORT TERM...NPB
LONG TERM...Martin
AVIATION...NPB
CLIMATE...Evans