064
FXUS61 KCTP 301725
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
125 PM EDT TUE JUN 30 2026
WHAT HAS CHANGED
* CONFIDENCE IN A PROLONGED HEAT SPELL HAS INCREASED, AND HEAT
PRODUCTS HAVE BEEN ISSUED INTO SATURDAY FOR AFFECTED AREAS.
* BUMPED POPS UP FOR ISOLD-SCT SHRA/TSRA THIS PM AND WED PM
KEY MESSAGES
1) SIGNIFICANT, LONG DURATION, AND DANGEROUS HEAT WAVE EXPECTED
FROM THE LAST DAY OF JUNE INTO INDEPENDENCE DAY/4TH OF JULY
HOLIDAY WEEKEND
2) ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS POSSIBLE
TUESDAY AND WEDNESDAY AFTERNOON/EVENING
DISCUSSION
KEY MESSAGE 1: SIGNIFICANT, LONG DURATION, AND DANGEROUS HEAT
WAVE EXPECTED FROM THE LAST DAY OF JUNE INTO INDEPENDENCE
DAY/4TH OF JULY HOLIDAY WEEKEND
THE MAIN ISSUE AND OVER-ARCHING MESSAGE IS THE EXCESSIVE HEAT
THROUGHOUT THE REMAINDER OF THE WEEK AND EVEN INTO THE 4TH. THE
BIG UPPER RIDGE OVER THE OH/TN VALLEYS WILL SHIFT EAST AND A
LITTLE NORTH THROUGH THE NEXT SEVERAL DAYS. ABUNDANT SUNSHINE
AND HIGH MOISTURE WILL MAKE BEING OUTSIDE FEEL INCREDIBLY
UNCOMFORTABLE. AS WE HAVE BEEN MESSAGING FOR MANY DAYS, WE
EXPECT A SPELL OF 5 DAYS OF HEAT INDICES OVER 100 FOR AT LEAST
PART OF THE CWA. THE PEAK OF THE HEAT AND HUMIDITY WILL BE
WEDNESDAY AND THURSDAY WITH NEARLY IDENTICAL HEAD INDEX VALUES
BOTH AFTERNOONS. MUCH OF THE AREA WILL HAVE HEAT INDICES
BETWEEN 100 AND 110 THOSE TWO DAYS. DUE TO THE HIGH CONFIDENCE
IN THAT PART OF THE FORECAST, WE HAVE ISSUED APPROPRIATE
EXCESSIVE HEAT WARNINGS AND HEAT ADVISORIES FOR THE NEXT FEW
DAYS. THE HUMIDITY CREEPS INTO WARREN CO TODAY, WHILE THE
DEWPOINTS STAY IN THE 60S IN THE SE. THE HEAT EXPANDS ON WED
WITH TEMPERATURES NEARING 100 IN THE URBAN AREAS OF EAST. WE'VE
MADE VERY MINOR TWEAKS TO THE TEMPS AND DEWPOINTS EACH DAY IN
COLLABORATION WITH THE NEIGHBORS. THE HEAT WILL START TO ABATE
FRI AND A LITTLE MORE SAT. NOT MUCH, BUT LIKELY ENOUGH TO START
TAPERING OFF THE ADVYS/WARNINGS.
AS WE HAVE BEEN ENCOURAGED TO DO, WE CHOSE TO USE THE LOW END
OF THE SCALE TO BASE THE WWAS. SO, WHILE ON THE FORECAST MAP,
>=50% OF CAMBRIA CO DOES NOT GET TO 100HI ANY DAY, WE FELT IT
WAS WISE TO INCLUDE THEM IN THE ADVY DUE TO JOHNSTOWN'S FEW
PIXELS THAT DO REACH 100. MANY OF THE PEOPLE MOST VULNERABLE TO
HEAT STRESS/ILLNESSES LIVE IN THE URBAN AREA OF THE CONEMAUGH
VALLEY. ALSO, WE CONSIDERED LEAVING MCKEAN AND POTTER COUNTIES
OUT OF THE HEAT ADVYS, BUT DECIDED TO INCLUDE THEM AS THERE WERE
A FEW PIXELS OF 100HI THERE, AND KEEPING IN MIND THAT NY
STATE'S THRESHOLD FOR ADVY IS ONLY 95 (PA IS 100). NOW, SOMERSET
CO IS THE ODD MAN OUT FOR THIS GO 'ROUND. WE'VE LEFT THEM OUT
OF THE ADVYS BECAUSE THEIR HEAT INDEX NUMBERS JUST WEREN'T
CLOSE ENOUGH TO MAKE A STRONG CASE FOR INCLUSION BASED ON
FORECASTER JUDGMENT/NUDGERS. THIS MATCHES WITH LWX LEAVING
THEIR HIGHEST- ELEVATION COS OUT OF THE PRODUCTS - FOR NOW.
HEIGHT FALLS HAIL THE APPROACH OF A MINOR COLD FRONT WHICH
SHOULD ARRIVE ON FRIDAY OR SATURDAY. NATURAL FIREWORKS FOR THE
4TH. THE INCREASED CLOUD COVER AND SOME RAIN SHOULD HELP KNOCK
DOWN THE TEMPS, AND KNOCK OUT MOST WORRIES FOR HEAT PRODUCTS.
TEMPS IN THE SE HALF OF THE CWA WILL COME DOWN 3-5F FOR SAT
(FROM THE 100S OF FRIDAY). SO, IT WON'T BE A BIG CHANGE, BUT
PROBABLY ENOUGH TO DROP THE ADVYS FOR THE NW AND DOWNSHIFT THE
WARNING TO AN ADVY FOR THE SE HALF. SUNDAY SHOULD BE "COLD"
ENOUGH TO BE DONE WITH HEAT PRODUCTS. IT WILL LIKELY NOT BE UNTIL
MONDAY OR TUESDAY OF NEXT WEEK WHEN WE SEE HIGHS RETURN TO THE
MID TO UPPER 80S ACROSS CENTRAL PA.
-------------------------------------------------------
KEY MESSAGE 2: 2) ISOLATED TO SCATTERED SHOWERS AND
THUNDERSTORMS POSSIBLE TUESDAY AND WEDNESDAY AFTERNOON/EVENING
CHANGES HAVE BEEN VERY MINOR WITH THE MAIN CHANGE NUDGING POPS
UP THIS AFTN/EVENING AND WED AFTN/EVENING WITH TWO SHORTWAVE
TROUGHS ROLLING OVER THE STRONG UPPER RIDGE AND NIPPING THE N
AND E WITH SOME FORCING. THIS FORCING, COMBINED WITH THE
HELP/LIFT OF THE CENTRAL PA RIDGES, SHOULD BE ENOUGH TO TRIGGER
A COUPLE OF SHRA/TSRA. SPC GENERAL THUNDER SUPPORTS THIS IDEA,
BUT MOST SHOULD BE N & E OF THE CWA. A WILD CARD WILL BE THE SE
THIRD OF THE AREA ON WED, WHERE CAPES GET SUPER HIGH AND THE
POSSIBLE DIP IN UPPER TEMPS MAY ALLOW ISOLD/SCT STORMS TO POP UP
THERE. IN COLLAB WITH PHI AND LWX, WE ADDED 20-30 POPS THERE FOR
WED PM.
AVIATION /18Z TUESDAY THROUGH SUNDAY/
BROAD HIGH PRESSURE OVER THE NORTHEASTERN US WILL SHIFT
TOWARDS THE TENNESSEE VALLEY THROUGHOUT TODAY, BRINGING
SOUTHWEST WINDS OF 5-10 KTS WITH A FEW GUSTS OF 15 TO 20 KNOTS
POSSIBLE IN THE AFTERNOON. MOREOVER, A VFR SCT-BKN CUMULUS DECK
WILL DEVELOP DURING THE MORNING & EARLY AFTERNOON HOURS, WITH A
FEW AFTERNOON SHOWERS/THUNDERSTORMS POSSIBLE ACROSS NORTHERN PA.
HOWEVER, GUIDANCE CONTINUES TO BRING HIGHER STORM CHANCES (>30%
CHANCE) TOWARDS UPSTATE NY & NEW ENGLAND WHERE LESS CAPPING IS
IN PLACE, PRECLUDING TAF MENTIONS OF SHOWERS/STORMS AT THIS
TIME.
FOR TONIGHT, VFR WILL CONTINUE TO PREVAIL WITH SCT-BKN CUMULUS
REMAINING OVERHEAD & FOG REMAINING UNLIKELY AT OUR TAF SITES. A
20-30 KT LLJ (BELOW LLWS THRESHOLDS) WILL DEVELOP DURING THE
EVENING IN RESPONSE TO A TIGHTENING PRESSURE GRADIENT ON THE
PERIPHERY OF THE HIGH PRESSURE, WITH 925 MB WINDS VEERING FROM
SW TO W/WNW THROUGH THE NIGHT.
OUTLOOK...
TUE-SAT...AM FOG; OTHERWISE VFR. TRENDING HOTTER WITH ISOLD PM
T-STORMS PSBL. HIGH DENSITY ALTITUDE CONCERNS POSSIBLE.
CLIMATE
TRIPLE DIGIT MAX TEMPS ARE FORECAST IN THE LOWER SUSQ VALLEY
(LSV) ON THURSDAY AND FRIDAY BOOKENDED BY UPPER 90S WEDNESDAY
AND SATURDAY.
THE LAST TIME HARRISBURG OBSERVED CONSECUTIVE DAYS WITH MAXT
GREATER THAN OR EQUAL TO 100F WAS BACK IN 2011 ON JULY 21-22.
THE RECORD NUMBER OF CONSECUTIVE DAYS WITH MAXT >= 100F IS 3
AND HAS OCCURRED 5 TIMES: (ALL IN THE MONTH OF JULY)
1999-07-16 TO 1999-07-18
1999-07-04 TO 1999-07-06
1991-07-19 TO 1991-07-21
1966-07-02 TO 1966-07-04
1936-07-09 TO 1936-07-11
THE LAST TIME HARRISBURG HIT THE CENTURY MARK WAS JULY 16TH IN
2024. PRIOR TO THAT, IT WAS JULY 19TH IN 2020.
HARRISBURG AVERAGES 1 DAY ANNUALLY WITH A MAXT >100F. THE MOST
NUMBER OF DAYS OBSERVED IN A YEAR IS 6 IN 1999.
CTP WATCHES/WARNINGS/ADVISORIES
HEAT ADVISORY UNTIL 8 PM EDT FRIDAY FOR PAZ004.
HEAT ADVISORY FROM NOON WEDNESDAY TO 8 PM EDT FRIDAY FOR
PAZ005-006-010>012-017-018-024-025-034-035-037-041-042.
EXTREME HEAT WARNING FROM NOON WEDNESDAY TO 8 PM EDT FRIDAY
FOR PAZ019-026>028-036-045-046-049>053-056>059-063>066.
HEAT ADVISORY FROM 8 PM FRIDAY TO 8 PM EDT SATURDAY FOR PAZ019-
026>028-036-045-046-049>053-056>059-063>066.
AIR QUALITY ALERT UNTIL MIDNIGHT EDT TONIGHT FOR PAZ057-059-
063-065-066.
WHAT HAS CHANGED...DANGELO/BOWEN
KEY MESSAGES...DANGELO/BOWEN
DISCUSSION...DANGELO/BOWEN
AVIATION...BAUCO/TEARE
CLIMATE...STEINBUGL
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