949
FXUS61 KCTP 300533
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
133 AM EDT TUE JUN 30 2026
WHAT HAS CHANGED
* HEAT ADVISORY FOR WARREN COUNTY NOON TUESDAY-10PM THURSDAY
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
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 EVENT FOR THIS WEEK WILL BE THE HEAT WAVE BEGINNING
TUESDAY (LAST DAY OF JUNE) INTO THE INDEPENDENCE DAY/4TH OF JULY
HOLIDAY WEEKEND.
FOR THE REST OF THE AFTERNOON, WE CAN'T RULE OUT A LOCALIZED,
TERRAIN INDUCED, SOUTHWARD DRIFTING RAIN SHOWER OR BRIEF
THUNDERSTORM OVER THE SOUTHERN POCONOS INTO THE SOUTH CENTRAL
ALLEGHENIES. A MAINLY CLEAR AND MUGGY OVERNIGHT PERIOD SHOULD
ALLOW FOR GOOD VIEWING OF THE STRAWBERRY MOON AND MAY ALSO
ALLOW FOR PATCHY FOG TOWARD DAYBREAK.
A VERY STRONG RIDGE BECOMING ANCHORED OVER THE EASTERN HALF OF
THE COUNTRY WILL SUPPORT A SIGNIFICANT, LONG DURATION, AND
DANGEROUS HEAT WAVE IMPACTING CENTRAL PA. MAX HEAT INDEX VALUES
BETWEEN 95 AND 110 DEGREES ARE FORECAST DURING THE AFTERNOON AND
EVENING TUESDAY THROUGH SUNDAY WITH WARM AND MUGGY CONDITIONS
OFFERING LITTLE TO NO OVERNIGHT RELIEF. THIS EQUATES TO
WIDESPREAD MAJOR TO EXTREME HEATRISK. WE INCREMENTALLY ISSUED A
HEAT ADVISORY FOR WARREN COUNTY WITH THE EXPECTATION OF FUTURE
EXPANSION OF HEAT HEADLINES TO EVENTUALLY COVER ALL OF CENTRAL
PA IN THE COMING SHIFTS.
THE GREATEST FORECAST CHALLENGE (HIGHEST UNCERTAINTY/LOWEST
CONFIDENCE) CONTINUES TO CENTER AROUND RING OF FIRE CONVECTION
THAT COULD SPILL SOUTHEASTWARD AROUND THE NORTHERN PERIPHERY OF
THE UPPER RIDGE INTO THE AREA. SPC HAS SHIFTED THE LEVEL 1/5
MRGL RISK A BIT FARTHER TO THE NORTHEAST AND ESSENTIALLY OUT OF
THE FORECAST AREA/CWA FOR TUESDAY. HOWEVER, INHERENT UNCERTAINTY
IN THESE TYPES OF PATTERNS WILL KEEP LOWER RAIN/THUNDERSTORM
CHANCES IN THE FORECAST THROUGH THE WEEKEND.
AVIATION /06Z TUESDAY THROUGH SATURDAY/
VFR CONDITIONS ARE EXPECTED AT ALL TAF SITES THROUGH THE NIGHT
AS BROAD HIGH PRESSURE SITS OVER THE NORTHEASTERN US, WITH A FEW
PASSING HIGH CLOUDS AND LIGHT WINDS. SOME PATCHY OVERNIGHT
VALLEY FOG IS LIKELY TO FORM, ALBEIT LESS EXTENSIVE THAN IT HAS
BEEN THE PAST COUPLE OF NIGHTS, WITH ANY FOG FORECAST TO MIX
OUT BY 15Z TUESDAY. JST, AOO, UNV, AND IPT HAVE AROUND A 30
PERCENT CHANCE OF SEEING VISIBILITY DROP BELOW 6SM, AND CHANCES
ARE EVEN LOWER AT THE OTHER TAF SITES.
THE HIGH PRESSURE WILL SHIFT TOWARDS THE TENNESSEE VALLEY ON
TUESDAY, 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 TUESDAY NIGHT, 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 FROM NOON TODAY TO 10 PM EDT THURSDAY FOR PAZ004.
EXTREME HEAT WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY
EVENING FOR PAZ019-026>028-035-036-045-046-049>053-056>059-
063>066.
WHAT HAS CHANGED...STEINBUGL
KEY MESSAGES...STEINBUGL
DISCUSSION...STEINBUGL
AVIATION...BAUCO/BOWEN/TEARE
CLIMATE...STEINBUGL
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