375
FXUS61 KCTP 290510
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
110 AM EDT MON JUN 29 2026
WHAT HAS CHANGED
* INCLUDED NEAR-TERM POTENTIAL OF SHOWERS AND THUNDERSTORMS
PRODUCING ISOLATED INSTANCES OF FLASH FLOODING IN THE LAUREL
HIGHLANDS, SEE KEY MESSAGE #2.
* CONFIDENCE IS STILL HIGH IN LONG-DURATION HEAT THIS WEEK
BEGINNING TUESDAY AND CONTINUING INTO THE HOLIDAY WEEKEND.
KEY MESSAGES
1) SIGNIFICANT, PROLONGED, AND DANGEROUS HEAT WAVE EXPECTED
FROM THE LAST DAY OF JUNE INTO INDEPENDENCE DAY/4TH OF JULY
HOLIDAY WEEKEND
2) SLOW-MOVING SHOWERS AND STORMS ACROSS THE LAUREL HIGHLANDS
THIS AFTERNOON COULD CAUSE ISOLATED INSTANCES OF FLASH FLOODING.
DISCUSSION
KEY MESSAGE 1: SIGNIFICANT, PROLONGED, AND DANGEROUS HEAT WAVE
EXPECTED FROM THE LAST DAY OF JUNE INTO INDEPENDENCE DAY/4TH OF
JULY HOLIDAY WEEKEND
WIDESPREAD TEMPERATURES IN THE 90S TO 100F, COMBINED WITH HIGH
HUMIDITY, WILL RESULT IN FORECAST MAX HEAT INDEX VALUES IN THE
100-110F RANGE WITH THE HIGHEST VALUES IN THE LOWER ELEVATIONS
TO THE EAST OF THE ALLEGHENY MOUNTAINS. THIS EQUATES TO
WIDESPREAD MAJOR-TO-EXTREME HEATRISK FROM WEDNESDAY THROUGH
FRIDAY OR SATURDAY ACROSS CENTRAL PENNSYLVANIA. ADDITIONAL WATCH
CONSIDERATIONS WERE GIVEN THIS CYCLE; HOWEVER, BASED ON
COLLABORATION WITH NEIGHBORS DECIDED TO HOLD OFF ON HEADLINES TO
GET ANOTHER CYCLE TO GAUGE WHICH ZONES WILL BE CLOSER TO UPPER-
END HEAT ADVISORY CRITERIA VERSUS LOWER-END EXTREME HEAT
WARNING CRITERIA. FOR ZONES CLOSE TO THE ADVISORY/WARNING
THRESHOLD, MAIN UNCERTAINTIES WITH HEAT INDEX VALUES REACHING
ABOVE OR REMAINING BELOW 105F WILL BE DEWPOINTS, WHICH TYPICALLY
TREND BELOW NBM MODEL GUIDANCE IN THESE TYPES OF SET-UPS WITH
DRIER AIR MIXING DOWN TO THE SURFACE. OVERNIGHT LOW TEMPERATURES
THROUGHOUT THIS TIMEFRAME WILL REMAIN QUITE WARM, BRINGING
LITTLE TO NO RELIEF FROM THE HEAT IN THE NIGHTTIME HOURS.
THE GREATEST FORECAST CHALLENGE (HIGHEST UNCERTAINTY/LOWEST
CONFIDENCE) CENTERS AROUND RING OF FIRE CONVECTION THAT COULD
SPILL SOUTHEASTWARD AROUND THE NORTHERN PERIPHERY OF THE UPPER
RIDGE INTO THE AREA ON FRIDAY; HOWEVER, EC/GFS MODEL GUIDANCE
HAVE BOTH STARTED TO SHOW SOME PRECIPITATION MENTIONS IN MORE
RECENT MODEL GUIDANCE, SO THIS TIMEFRAME WILL BEAR WATCHING AS
WE GET CLOSER TO THE END OF THE WEEK.
---------------------------------------------------------------
KEY MESSAGE 2: SLOW-MOVING SHOWERS AND STORMS ACROSS THE LAUREL
HIGHLANDS THIS AFTERNOON COULD CAUSE ISOLATED INSTANCES OF
FLASH FLOODING.
CURRENT RADAR AS OF 2:30 EDT OUTLINES SCATTERED SHOWERS AND
THUNDERSTORMS ACROSS PORTIONS OF WESTERN PENNSYLVANIA IN AN
ENVIRONMENT WITH AMPLE MOISTURE IN PLAY. RECENT HREF ENSEMBLE
GUIDANCE OUTLINES PWATS THIS AFTERNOON/EVENING SLIGHTLY ABOVE
1.50" WHICH APPEARS TO BE IN THE 80TH-90TH PERCENTILE FOR JUNE
28TH ACROSS THE SOUTHWESTERN PENNSYLVANIA. STORM MOTIONS HAVE
OVERALL BEEN VERY SLOW, THUS ANY AREA THAT RECEIVES MULTIPLE
SHOWERS AND STORMS THIS AFTERNOON COULD EXPERIENCE ISOLATED
INSTANCES OF FLASH FLOODING. RECENT WPC EROS OUTLINE THIS
POTENTIAL WITH THE BULK OF ACTIVITY OCCURRING TO THE WEST/SOUTH
OF CENTRAL PENNSYLVANIA; HOWEVER, HYDROLOGICALLY SENSITIVE
AREAS IN SOUTHERN SOMERSET COUNTY COULD ALSO RUN INTO THESE
INSTANCES OF FLASH FLOODING. FURTHER NORTH, COVERAGE IS EXPECTED
TO BE SLIGHTLY LESS AND MANY AREAS WILL LIKELY NOT RECEIVE
MULTIPLE ROUNDS OF HEAVY RAINFALL TO WARRANT MUCH IN THE WAY OF
FLOODING CONCERNS THIS EVENING.
RAIN CHANCES DIMINISH AFTER SUNSET, WITH FOG FORMATION LIKELY
TO OCCUR OVERNIGHT INTO MONDAY MORNING. FOG IS NOT EXPECTED TO
BE AS EXPANSIVE AS LAST NIGHT; HOWEVER, COULD SEE SOME LOCALLY
DENSE FOG ACROSS THE HIGHER ELEVATIONS OF SOMERSET COUNTY WHERE
THE AFOREMENTIONED HEAVY RAIN IS EXPECTED TODAY. ANY FOG IS
EXPECTED TO MIX OUT QUICKLY AFTER SUNRISE MONDAY MORNING, BUT
COULD STILL BE AROUND FOR THE MONDAY MORNING COMMUTE.
AVIATION /06Z MONDAY THROUGH FRIDAY/
FORECAST REMAINS ON TRACK: THE MAIN CONCERN OVERNIGHT WILL BE
FOG FORMATION. MOST GUIDANCE INDICATES THAT FOG MAY BE FAIRLY
WIDESPREAD, WITH ALL TAF SITES POTENTIALLY SEEING VISIBILITY
RESTRICTIONS AT TIMES DURING THE NIGHT. WHILE JST AND AOO APPEAR
MOST LIKELY TO SEE VISIBILITY AS LOW AS 1/4SM, ALL SITES WILL
HAVE AT LEAST SOME CHANCE OF SEEING VISIBILITY BELOW 1SM.
CONFIDENCE IN FOG FORMATION IS LOWEST AT BFD AND IPT.
VFR CONDITIONS WILL RETURN AREA-WIDE BY 15Z AS THE FOG
DISSIPATES. MONDAY WILL FEATURE LIGHT WINDS AND CONTINUED VFR
CONDITIONS WITH SCATTERED CLOUDS. A FEW SHOWERS MAY DEVELOP IN
THE AFTERNOON, BUT CONFIDENCE IN TIMING, PLACEMENT, AND COVERAGE
IS TOO LOW TO CONSIDER ANY MENTIONS OF RAIN IN THE TAFS.
OUTLOOK...
TUE-FRI...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
NONE.
WHAT HAS CHANGED...BEATY
KEY MESSAGES...BEATY
DISCUSSION...BEATY
AVIATION...BAUCO/TEARE
CLIMATE...STEINBUGL
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