Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 071440 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1040 AM EDT TUE JUL 7 2015 .SYNOPSIS... A WEAKENING UPPER LOW WILL TRACK EAST OF THE REGION THIS MORNING. A WEAK RIDGE WILL BRING VERY WARM AND HUMID CONDITIONS TO THE REGION TODAY. A COLD FRONT WILL APPROACH TONIGHT...THEN STALL OUT ALONG...OR JUST SOUTH OF THE MASON DIXON LINE FOR THE MID TO LATE WEEK PERIOD. A FEW WAVES OF LOW PRESSURE WILL RIPPLE EAST ALONG THIS BOUNDARY BRINGING THE LIKELIHOOD FOR SHOWERS AND THUNDERSTORMS WEDNESDAY AFTERNOON AND EVENING...AND AGAIN ON THURSDAY. HIGH PRESSURE WILL BUILD IN FOR FRIDAY AND BRING SLIGHTLY COOLER AND NOTABLY LESS HUMID WEATHER WITH LITTLE CHANCE FOR RAIN. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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AS AN UPPER LEVEL TROUGH EXITS THE REGION EARLY THIS AFTERNOON EXPECT SOME CLEARING FROM WEST TO EAST AND A MIX OF CLOUDS AND SUN FOR THE REST OF THE DAY. HIGH TEMPERATURES TODAY WILL TOP OUT A FEW DEGREES ABOVE NORMAL THANKS TO DEEP WEST /SOUTHWEST FLOW AND INCREASING SUNSHINE. MOST OF THE AREA WILL REMAIN DRY THROUGH THE EVENING AS WE EXPERIENCE A PERIOD OF WIDESPREAD SUBSIDENCE. THIS PERIOD IS SHORTLIVED AS A COLD FRONT APPROACHES NORTHWEST PENNSYLVANIA THIS EVENING. SOME STRONG MULTICELL THUNDERSTORM CLUSTER ARE LIKELY TO FORM AS THE FRONT CROSSES INTO THE NORTHWEST ZONES THIS EVENING. **SOME CONCERN THAT A WEAK LEE TROUGH OVER...AND TO THE EAST OF THE SUSQ VALLEY WITH A SLIGHT WEAKNESS IN THE MID LEVEL CAP /NOTED BY A RIBBON OF 700 MB TEMPS OF AROUND 6C/ COUPLED WITH THE CLOSE PROXIMITY OF THE EXIT REGION OF AN UPPER LEVEL JETLET COULD SPARK ISOLATED-SCT COVERAGE OF PULSE SHRA/TSRA FOR A FEW HOURS DURING THE MID TO LATE AFTERNOON.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... SFC COLD FRONT SLIDES SLOWLY TO THE SOUTHEAST ACROSS THE COMMONWEALTH TONIGHT THROUGH WED MORNING...BEFORE STALLING OUT NEAR...OR JUST TO THE SOUTH OF THE MASON-DIXON LINE. MAIN FCST PROBLEM/CHALLENGE FOR THE UPCOMING SHIFTS WILL BE TO TRY TO PIN DOWN /VIA SOME SEMBLANCE OF MODEL CONSENSUS/ THE LOCATION AND TIMING OF CONVECTIVE FEATURES/AREAS OF LOW PRESSURE THAT WILL FORM AND RIDE EAST ALONG THIS BOUNDARY WEDNESDAY INTO THURSDAY. CURRENTLY...A GEFS/NAM/SREF BLEND POINT TWD THE BEST CHC FOR RAIN WITH EMBEDDED TSRA FOCUSED ACROSS THE SOUTHERN THIRD TO HALF OF PENN WEDNESDAY...WHERE PWAT WILL STAY AOA 2.0 INCHES. THE SHARP GRADIENT TO MUCH LOWER PWAT /AOB 0.75 OF AN INCH/ WILL STAY NEAR OR JUST TO THE NORTH OF THE PENN/NEW YORK BORDER WHERE CHCS FOR RAIN WILL BE QUITE LOW WEDNESDAY AND MOST OF WED NIGHT. MAX TEMPS WEDNESDAY COULD EASILY TURN OUT TO BE SEVERAL DEG F OR MORE BELOW CURRENT FCST VALUES DEPENDING ON THE TIMING AND EXTENT OF CONVECTION ACROSS THE CENTRAL AND SOUTH. CURRENT TEMP FCST BUSTING ON THE LOW SIDE FOR WEDNESDAY`S HIGH IS A VERY LOW PROBABILITY. WILL BE ADJUSTING THESE TEMPS WITH 03Z SREF AND 06Z OP GUIDANCE WHERE NEEDED. && .LONG TERM /THURSDAY THROUGH MONDAY/... THE LINGERING QUASI-STATIONARY FRONTAL ZONE EXTENDING FROM THE MID ATLANTIC COAST WWD INTO THE OHIO VALLEY IS EXPECTED TO REMAIN A FOCUS FOR PCPN ON DAY 3/THURS. THERE IS REASONABLY GOOD MODEL AGREEMENT IN A CONVECTIVELY ENHANCED PERTURBATION/SFC WAVE EMERGING FROM THE SRN PLAINS AND PROGRESSING EWD AROUND THE PERIPHERY OF A SUBTROPICAL RIDGE OVER THE SOUTHEAST STATES. THE GLOBAL MODELS TEND TO HAVE A NORTHERN BIAS WITH QPF AXES ASSOCD WITH THESE MESO FEATURES...AND THEREFORE FOLLOWED WPC LEAD WITH CLUE FROM THE HI-RES MODELS IN SHIFTING MAX POPS SWD OF CONSENSUS. THERE IS THE POTENTIAL FOR THIS FEATURE TO MAINTAIN INTENSITY OR RE-INTENSIFY AS IT REACHES CENTRAL PA THURSDAY AFTERNOON..IN WHICH CASE IT WOULD BE ACCOMPANIED BY SEVERE WX AND HEAVY RAINFALL RISK. LATER FORECASTS SHOULD BE ABLE TO PROVIDE GREATER VISIBILITY AND INCREASED CONFIDENCE IN THE EVOLUTION AND POTENTIAL IMPACTS ASSOCD WITH THIS SYSTEM. THE MEDIUM RANGE MODEL AND ENSEMBLE GUIDANCE REMAINS CONSISTENT IN ITS PROJECTION THAT THE FLOW ALOFT WILL STEADILY EVOLVE TOWARD AN AMPLIFIED TROUGH/RIDGE/TROUGH PATTERN FROM WEST TO EAST ACROSS THE LOWER 48. THIS SHOULD OCCUR BY WAY OF NRN PAC ENERGY FEEDING INTO A TROUGH ALONG THE WEST COAST...A STRENGTHENING UPPER RIDGE THAT RETROGRADES WWD FROM THE SOUTHEAST INTO THE PLAINS EVENTUALLY EXPANDING NWD OVER THE ROCKIES INTO WRN CANADA...AND DOWNSTREAM TROUGHING FROM THE BUILDING RIDGE OVER THE EAST EXTENDING SWD FROM HUDSON BY VORTEX. A 24-48HR PERIOD OF DRY WEATHER...WHICH HAS BEEN QUITE ELUSIVE AS OF LATE...COULD BE IN STORE FOR THE AREA BY THE END OF THE WEEK AS WEAK RIDGING FOLLOWS IN THE WAKE OF THE D3 CONVECTIVE LOW. THE PLACEMENT OF PIVOTING FRONTAL BOUNDARY AND ASSOCIATED MSTR/PW AXIS WILL BE CRUCIAL FOR DETERMINING PCPN RISK INTO THE WEEKEND...WITH THE LATEST MODEL CONSENSUS KEEPING MOST OF THE ACTIVITY TO THE NW OR SW OF CENTRAL PA. THE OTHER FACTOR WILL BE WHAT HAPPENS TO ENERGY EJECTING FROM UPPER LOW MOVING ONSHORE CA IN THE SHORT RANGE. THERE IS REASONABLE AGREEMENT IN PRINCIPLE THAT THIS ENERGY SHOULD ROUND THE BUILDING ROCKIES/HIGH PLAINS RIDGE AND THEN HELP TO CARVE OUT THE DEVELOPING ERN TROUGH DOWNSTREAM. HOWEVER SOLUTIONS HAVE NOT LOCKED ONTO HOW SHEARED THE ENERGY WILL BECOME...WHICH ALONG WITH A FEW ADDITIONAL FACTORS LEADS TO DIFFERENCES IN THE DEPTH OF THE TROUGH AND TIMING OF NEXT PCPN OPPORTUNITY. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/...
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CURRENT MVFR CONDITIONS ARE EXPECTED TO IMPROVE THIS AFTERNOON AS THE LOW CLOUDS BURN OFF. AS A COLD FRONT APPROACHES THIS EVENING THUNDERSTORMS ARE LIKELY TO FORM AND IMPACT BFD TONIGHT WITH MVFR CONDITIONS. THE COLD FRONT WILL PUSH SLOWLY SEWD ACROSS THE AIRSPACE OVERNIGHT INTO WEDNESDAY BEFORE STALLING OUT WEST-TO-EAST ALONG THE OH RIVER AND MASON DIXON LINE. WAVES OF LOW PRESSURE WILL MOVE ALONG THE FRONT AND BRING PERIODS OF SHOWERS/TSTMS AND REDUCED CONDITIONS LATER WEDNESDAY INTO THURSDAY. OUTLOOK... FRI-SAT...MAINLY VFR. CHC OF SHOWERS/TSTMS SW 1/3 OF AIRSPACE.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LA CORTE/LAMBERT NEAR TERM...LA CORTE/LAMBERT/KEARNS SHORT TERM...LAMBERT LONG TERM...STEINBUGL AVIATION...LA CORTE/STEINBUGL

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