981
FXUS61 KCTP 281805
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
205 PM EDT SUN JUN 28 2026
WHAT HAS CHANGED
INCREASING CONFIDENCE IN A LONG LASTING HEAT WAVE TUESDAY INTO
INDEPENDENCE DAY/4TH OF JULY
KEY MESSAGES
1) SIGNIFICANT, PROLONGED, AND DANGEROUS HEAT WAVE EXPECTED
FROM THE LAST DAY OF JUNE INTO INDEPENDENCE DAY/4TH OF JULY
HOLIDAY WEEKEND
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
CONFIDENCE AND PREDICTABILITY REMAINS HIGH FOR A LARGE AND
ANOMALOUS 590+DM UPPER LEVEL RIDGE TO DELIVER A SIGNIFICANT,
MULTIDAY, AND POTENTIALLY DANGEROUS HEAT WAVE FROM THE LAST DAY
OF JUNE (TUESDAY 6/30) INTO INDEPENDENCE DAY/4TH OF JULY HOLIDAY
WEEKEND.
WIDESPREAD TEMPERATURES IN THE 90S TO 100F, COMBINED WITH HIGH
HUMIDITY, WILL RESULT IN FCST MAX HEAT INDICES 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 AND HIGH PROBABILITY OF HEAT WWA
HEADLINES FROM WEDNESDAY THROUGH FRIDAY OR SATURDAY.
(CONSIDERATION WAS GIVEN TO AN EXTREME HEAT WATCH WITH THIS
CYCLE PER COORDINATION WITH PHI). OVERNIGHT LOWS WILL ALSO BE
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 LATE IN THE WEEK.
---------------------------------------------------------------
IN THE SHORTER TERM, LOW STRATUS AND FOG EARLY THIS MORNING WILL
GIVE WAY TO MOSTLY CLOUDY CONDITIONS INTO THE AFTERNOON WITH
SPOTTY SHOWERS/THUNDERSHOWERS POSSIBLE. HREF/REFS ARE KEYING ON
SOUTHWEST PA INTO THE LAUREL HIGHLANDS WITH THE HIGHEST PRECIP
PROBS BETWEEN 8AM-8PM. SOME CLEARING EXPECTED OVERNIGHT WHICH
ALLOWS FOR AREAS OF FOG TO DEVELOP AGAIN INTO EARLY MONDAY
MORNING.
AVIATION /18Z SUNDAY THROUGH FRIDAY/
DAYLIGHT HAS PERMITTED LOW STRATUS TO LIFT THROUGHOUT TODAY,
WITH GRADUAL IMPROVEMENTS TO MVFR-VFR CONTINUING THIS AFTERNOON.
A WEAK LOW PRESSURE SYSTEM PERSISTS ACROSS THE MID-ATLANTIC,
FORCING SCATTERED SHOWERS ACROSS THE COMMONWEALTH (ESPECIALLY
WHERE SPC MESOANALYSIS SHOWS OVERLAP OF PWATS AOA 1.5" + MLCAPE
UPWARDS OF 500 J/KG OVER SW PA). TALL/NARROW CAPE WILL FAVOR
RAINFALL EFFICIENCY GIVEN DEEP MOISTURE IN PLACE WITH LOW CHANCE
FOR LIGHTNING (LESS THAN PROB30, THOUGH NON-ZERO IN THE
HEAVIEST SHOWERS). VISIBILITY RESTRICTIONS TO MVFR-IFR ARE
POSSIBLE IN THE HEAVIER SHOWERS.
SHOWERS WILL TAPER OFF THIS EVENING & CLOUD COVER WILL TREND
SCT-BKN, BRINGING A CHANCE FOR RADIATIONAL MIST/FOG TONIGHT
GIVEN LOW-LEVEL MOISTURE FROM RECENT RAINFALL AND LIGHT/VARIABLE
WINDS AS HIGH PRESSURE BUILDS ACROSS THE NORTHEASTERN US. A
BLEND OF THE GLAMP AND HREF MODELS WERE USED FOR VISIBILITY,
WITH HIGHER PROBABILITIES (50-60%) OF OVERNIGHT FG AROUND THE
APPALACHIANS (KJST/KAOO). AFTER SUNRISE ON MONDAY, DAYLIGHT WILL
ONCE AGAIN MIX OUT THE LOWER STRATUS, GIVING WAY TO REGIONWIDE
VFR BY 15Z.
OUTLOOK...
MON-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...STEINBUGL
KEY MESSAGES...STEINBUGL
DISCUSSION...STEINBUGL
AVIATION...TEARE
CLIMATE...STEINBUGL
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