989
FXUS61 KCTP 300928
AFDCTP
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
528 AM EDT FRI MAY 30 2025
SYNOPSIS
* WET AND STORMY END TO ONE OF THE WETTEST MAY'S ON RECORD
* POTENTIAL FOR FLOODING AND STRONG WIND GUSTS IN THE LOWER
SUSQUEHANNA VALLEY LATE THIS EVENING THROUGH LATE TONIGHT
* STRETCH OF DRY WEATHER PROBABLE SUNDAY THROUGH TUESDAY WITH
TEMPERATURES WARMING UP TO SUMMERTIME LEVELS BY MIDWEEK
NEAR TERM /THROUGH TONIGHT/
LEAD SHORTWAVE ENERGY IS CURRENTLY DRIVING RAIN/SHOWERS ACROSS
THE DELMARVA INTO EASTERN/SOUTHEASTERN PA EARLY THIS MORNING.
MRMS RADAR INDICATES LIGHT RAIN HAS EXITED THE FAR SOUTHEAST
ZONES, LEAVING BEHIND A PARTLY TO MOSTLY CLOUDY START TO THE
LAST FRIDAY IN MAY WITH PATCHY FOG/LOW CLOUDS AND TEMPS IN THE
50-65 DEGREE RANGE.
EXPECT PATCHY FOG TO DISSIPATE IN MOST PLACES BY 9AM WITH A MIX
OF SUN AND CLOUDS INTO MIDDAY. LOOK FOR INCREASING CLOUDS AND
RAIN PROBS FROM WEST TO EAST THIS AFTERNOON INTO THE EVENING AS
SHOWERS AND TSTORMS DEVELOP AND TRACK EASTWARD INTO CPA FROM
THE UPPER OHIO VALLEY (SOUTHEAST OH/WV/SOUTHWEST PA) AFTER
18Z/2PM.
PRIMARY FORECAST CONCERNS IN THE NEAR TERM CENTER AROUND TWO
POTENTIAL WX HAZARDS: 1) HEAVY RAIN/FLOODING & 2) STRONG WINDS
1) WHILE IT'S NOT YET CLEAR IN TERMS OF EXACT LOCATION AND
AMOUNT, THE INDIVIDUAL CAMS ALONG WITH THE HREF/RRFS ARE
SIGNALING THE POTENTIAL FOR HEAVY RAIN ACROSS PARTS OF SOUTH
CENTRAL AND SOUTHEAST PA FROM LATE THIS EVENING INTO LATE
TONIGHT. IT'S HARD TO BELIEVE MOST OF THIS AREA WAS IN A
MODERATE TO SEVERE DROUGHT ONLY A FEW WEEKS AGO, BUT AFTER WHAT
COULD BE THE WETTEST MAY ON RECORD, THE FLOODING RISK IS VERY
PLAUSIBLE PARTICULARLY IN URBAN AREAS AND SMALL STREAM BASINS.
BLENDED HREF MEAN APPROACH (MEAN + PMM) ALONG WITH HEAVY
WEIGHTING OF HRRR DERIVED THE WPC QPF WHICH WAS UTILIZED FOR
THIS CYCLE; THE RESULT WAS 1-2" ACROSS THE LOWER SUSQ VALLEY
(ABOUT 1 INCH MORE THAN 24 HOURS AGO) WITH THE BULK OF THAT
TARGETED IN THE 00-06Z WINDOW. THE HEAVY RAINFALL OCCURRING IN
A RELATIVELY SHORT DURATION COMBINED WITH HREF NEIGHBORHOOD
PROBABILITIES OF EXCEEDING FFGS OVER A VULNERABLE/SATURATED AREA
OF THE CWA LEAD TO THE ISSUANCE OF A FLOOD WATCH IN COLLABORATION
WITH LWX/PHI. THE DAY SHIFT CAN ASSESS LATER ARRIVING HIRES
DATA AND CONSIDER A WESTWARD EXPANSION ALONG THE MD LINE.
2) 100-150M 12HR HEIGHT FALLS ASSOCIATED WITH POTENT MID/UPPER
TROUGH TAKING ON A NEGATIVE TILT AS IT CROSSES THE CENTRAL
APPALACHIANS WILL SPAWN A HIGHLY ANOMALOUS SFC LOW AROUND ~990MB
(MINUS 4 SIGMA MSLP/SEE CLIMATE SECTION FOR MORE INFO) OVER THE
NORTHERN CHESAPEAKE BAY/DELMARVA AREA IN THE 03-06Z TIMEFRAME
TONIGHT. NOT ONLY WILL THE STRONGLY FORCED SFC LOW (CYCLOGENESIS)
EVOLUTION DRIVE MODERATE TO HEAVY PRECIPITATION, BUT IT WILL
ALSO CARRY A STRONG WIND THREAT GIVEN THE DEPTH AND VERY TIGHT
PRESSURE GRADIENT. WIND GUSTS >40 MPH ARE NOT OUT OF THE
QUESTION OVER THE SOUTHEAST ZONES AND THIS WOULD CONSTITUTE A
SIGNIFICANT UPTICK IN THE WGUST FORECAST. THE COMMA
HEAD/DEFORMATION RAINFALL APPEARS TO ADD ANOTHER 0.25 TO 0.75"
BETWEEN 06-12Z AS THE HEAVY QPF AXIS SHIFTS TO THE NORTHEAST
ALONG THE PA/NY BORDER.
SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
AN APPROACHING COLD FRONT COINCIDING WITH A REINFORCING
SHORTWAVE ENERGY AND COOLING TEMPS ALOFT WILL FAVOR FREQUENT
SHOWER/ISOT ACTIVITY ON SATURDAY -- AND COULD EVEN BE ENOUGH TO
SUPPORT A MARGINAL WIND THREAT ACROSS EXTREME SOUTHEAST PA PER
THE SPC SWO FOR D2. MANUALLY ADJUSTED TEMPS CONTINUED TO FRONT
RUN THE NBM (LOWER) AND WIND GUSTS WERE INCREASED USING A BLEND
OF THE 90TH PERCENTILE. THE LAST DAY OF MAY WILL BE QUITE
BREEZY AND NOTICABLY COOLER WITH MAXT DEPARTURES FIRMLY 10 TO
15 DEGREES BELOW THE HISTORICAL AVERAGE.
TYPICAL STRATOCU FIELD IS LIKELY TO COVER AREAS DOWNWIND OF
LAKE ERIE SATURDAY NIGHT INTO SUNDAY MORNING WITHIN THE BRISK NW
FLOW REGIME. APPARENT TEMPS EARLY SUNDAY MORNING ARE FORECAST
IN THE 35-45F RANGE - WHAT A CHILLY START TO JUNE! THE UPPER
TROUGH MAY BE SLOWER TO DEPART AND THE 30/00Z EC IS EVEN MORE
PESSIMISTIC INTO EARLY NEXT WEEK. WORST CASE WOULD BE A FEW
LINGERING INSTABILITY SHOWERS, SO A DRIER TREND STILL HOLDS VS.
FRIDAY NIGHT/SATURDAY. LASTLY, THERE IS A LOW - BUT NON ZERO -
CHANCE FOR AT LEAST SOME PATCHY FROST OVER THE WESTERN
ALLEGHENIES SUNDAY NIGHT INTO MONDAY MORNING AS HIGH PRESSURE
BUILDS INTO THE REGION.
LONG TERM /MONDAY THROUGH THURSDAY/
HIGH PRESSURE SFC AND ALOFT BUILDS ACROSS THE SOUTHEAST PART OF
THE COUNTRY EARLY NEXT WEEK, WILL RESULT IN TEMPERATURES BEING
MORE NORMAL FOR EARLY JUNE. TEMPERATURES COULD BE ABOVE NORMAL
AT TIMES IN THE NEXT WEEK OR TWO.
LOOKS LIKE MOST OF THE TIME SUNDAY INTO WEDNESDAY WILL BE DRY
NEXT WEEK. THE NEXT COLD FRONT MAY BRING SOME SHOWERS AND
PERHAPS A STORM TO THE AREA NEXT THURSDAY.
GETTING TO THAT TIME OF YEAR, WHERE COLD FRONTS COULD STALL
ACROSS THE SOUTHEAST PART OF THE KEYSTONE STATE, AS WESTERLIES
LIFT TO THE NORTH. THIS IS ESPECIALLY THE CASE IF AN UPPER LEVEL
LOW LINGERS TO OUR SOUTH.
AVIATION /08Z FRIDAY THROUGH TUESDAY/
DETERIORATING CONDITIONS ARE LIKELY AGAIN TONIGHT, ESPECIALLY
AT MDT AND LNS AS LOWER CIGS AND SOME FOG PUSHES IN FROM THE
SOUTH ALONG WITH SOME RAIN. THE CHANCE FOR IFR CONDITIONS LATE
TONIGHT INTO EARLY FRI MORNING IS ABOUT 70 PCT AT LNS AND 60
PCT AT MDT. FARTHER NORTH/WEST, MOST LOCATIONS ARE EXPECTED TO
REMAIN VFR WITH THE EXCEPTION OF BFD AND JST, WHERE IFR CIGS
ARE POSSIBLE (50 PCT CHC) BEFORE DAYBREAK. SOME PATCHY FOG
CANNOT BE RULED OUT AT BFD EITHER.
CONDITIONS WILL IMPROVE FROM LATE MORNING TO EARLY AFTERNOON
TODAY, BEFORE DETERIORATING ONCE AGAIN LATER THIS AFTERNOON
INTO TONIGHT AS THE NEXT SYSTEM BRINGS PERIODS OF RAIN ACROSS
THE AREA, HEAVIEST IN THE SOUTHEAST. A FEW RUMBLES OF THUNDER
ARE POSSIBLE AT LNS AND MDT, BUT NOT ENOUGH CONFIDENCE TO
INCLUDE THUNDER AT THIS POINT IN THE TAFS.
THE MAIN BATCH OF RAIN WILL EXIT EAST OF THE AREA BY DAYBREAK
SATURDAY, THOUGH CEILING RESTRICTIONS WILL CONTINUE.
OUTLOOK...
FRIDAY AND FRIDAY NIGHT...SOME AFTERNOON/EVENING RESTRICTIONS
IN SCATTERED TO NUMEROUS SHOWERS AND A FEW THUNDERSTORMS.
SATURDAY AND SATURDAY NIGHT...MAINLY MVFR. SCATTERED PM SHOWERS
AND PERHAPS A THUNDERSTORM OR TWO IN THE VICINITY OF LNS AND
MDT. GUSTY NORTHWEST WINDS.
SUNDAY...MAINLY VFR WITH GUSTY NORTHWEST WINDS.
MONDAY-TUESDAY...VFR.
CLIMATE
MAY 2025 PRECIPITATION RANKINGS
SITE MAY 1-29, 2025 | WETTEST MAY ON RECORD
-----------------------------------------------------------
HARRISBURG 7.97" 2ND WETTEST | 9.71" IN 1989
WILLIAMSPORT 6.66" 6TH WETTEST | 9.91" IN 1919
ALTOONA 6.84" 3RD WETTEST | 7.31" IN 1960
STATE COLLEGE 6.47" 9TH WETTEST | 9.45" IN 1894
ADDITIONAL RAINFALL FORECAST AT HARRISBURG AND ALTOONA THROUGH
TONIGHT PUTS THE RECORDS FOR WETTEST MAY VERY MUCH IN JEOPARDY.
A SEASONABLY STRONG/DEEP AREA OF LOW PRESSURE (~990MB) IS
FORECAST TO MOVE ACROSS SOUTHEASTERN PENNSYLVANIA OVERNIGHT. THE
RECORD LOW PRESSURE FOR MAY AT HARRISBURG IS 983.4MB.
CTP WATCHES/WARNINGS/ADVISORIES
FLOOD WATCH FROM THIS EVENING THROUGH LATE TONIGHT FOR
PAZ064>066.
SYNOPSIS...STEINBUGL
NEAR TERM...STEINBUGL
SHORT TERM...STEINBUGL
LONG TERM...MARTIN
AVIATION...BANGHOFF/BOWEN
CLIMATE...STEINBUGL
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