Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 200341 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1141 PM EDT TUE AUG 19 2014 .SYNOPSIS... A MASSIVE RIDGE WILL BUILD OVER EAST-CENTRAL CANADA FOR THE NEXT WEEK. ANOTHER STRONG RIDGE WILL BUILD OVER THE SOUTHERN UNITED STATES. SHORT-WAVES EMBEDDED IN THE WEAK FLOW MOVING UNDER THE CANADIAN BLOCK WILL SLOW DOWN AND WEAKEN AS THEY MOVE THROUGH OUR REGION. THIS WILL LEAD TO A POTENTIALLY PROLONGED PERIOD OF UNSETTLED WEATHER. BUT IT SHOULD PROTECT US FROM THE LATE SEASON HEAT BUILDING TO OUR SOUTH. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... DRY CONDITIONS WILL PREVAIL FOR MOST OR ALL OF THE OVERNIGHT HOURS ACROSS SCENT PENN AND THE SUSQ VALLEY WITH PATCHY FOG FORMING AS A RESULT OF CLEAR TO PTLY CLOUDY SKIES...EARLIER SCATTERED EVENING SHOWERS...LIGHT AND VARIABLE WIND...AND MODERATELY HIGH SFC DEWPOINTS IN THE LOWER TO MID 60S. ACROSS THE WESTERN ZONES...INCREASING POPS WERE PAINTED IN AS A GRADUALLY WEAKENING LINE OF SHOWERS/TSRA SLIDES EAST FROM OHIO. ALTHOUGH THE BEST DYNAMIC FORCING /LINKED TO A COMPACT UPPER SHORTWAVE/ HEADS ENE ACROSS SOUTHERN NEW YORK...THE GREATEST ML INSTABILITY AND HIGHER PWAT AIR WILL BE FOCUSED ACROSS THE LAURELS. POPS WILL REACH CATEGORICAL 80-100 PERCENT ACROSS A FEW OF THE NW COUNTIES BETWEEN 03-06Z BEFORE GRADUALLY DECREASING FURTHER S AND E AS THE CONVECTION SLOWLY WEAKENS AND FRAGMENTS. SHORTWAVE RIDGING ALOFT OVER CENTRAL PENN FOR THE NEXT SEVERAL HOURS WILL MAINTAIN DRY AND PTLY CLOUDY CONDITIONS...WITH SCATTERED SHOWERS AND ISOLATED TSRA MOVING EAST INTO THE REGION AFTER 07Z. TEMPS WILL SLOWLY COOL OFF IN THE 60S IN ALL AREAS...REACHING FAIRLY UNIFORM LOWS IN THE LOWER 60S EARLY WED MORNING. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... A SURGE OF CAPE AND PW INTO WESTERN PA IN THE SREF AND NAM...SIMILAR TO OLDER GEFS/GFS IMPLY SOME MORE ORGANIZED RAIN POSSIBLE ON WEDNESDAY. USED A BLEND TO GET THE POPS AND THE 12KM NAM TO ADD SOME TEXTURE TO CONVECTION AND RAIN AREA THAT APPEARS TO BE POISED TO MOVE WEST TO EAST ACROSS THE REGION WEDNESDAY. THE SREF POPS/PDF IMPLIES SHOWERS COMING INTO WEST AROUND 1500 UTC AND MOST OF CENTRAL TWO THIRDS OF REGION BY LATE EVENING. SREF IS KIND OF OPTIMISTIC SOUTHEAST PA COULD HAVE YET ANOTHER MOSTLY RAIN FREE DAY WEDNESDAY. THE KEY FEATURES ARE THE RETROGRADING RIDGE OVER EASTERN CANADA WHICH IS TAKING THE UMPH OUT OF THE SYSTEMS CUTTING UNDER THIS FEATURE. IN MOST MODELS THE NEAR 1SD ABOVE NORMAL PW SURGES WEAKEN AS THE MOVE INTO PA. THUS MORE OPTIMISTIC...SREF-LIKE IN THE WEST THAN THE EAST WITH RAINFALL AND NOT REALLY CONFIDENT GOING LIKELY. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... THE WEAKENING RIDGE OVER EASTERN CANADA WILL ALLOW FOR DIVERGENT FLOW AS THE UPPER LEVEL LOW SLOWLY MOVES EASTWARD. DAYTIME HEATING...DECREASING PRESSURE...MOIST SOUTHEASTERLY SFC FLOW...AND WEST TO NORTHWESTERLY FLOW ALOFT SHOULD ALLOW FOR ENOUGH SHEAR...FOR CHANCE TO LIKELY POPS EARLY WEDNESDAY EVENING. CAPE VALUES ARE LOW...WITH AN AVG OF 500-1K J/KG THROUGHOUT MOST OF CENTRAL PA. SO SCATTERED SHOWERS AND THUNDERSTORMS REMAIN POSSIBLE EARLY WEDNESDAY EVENING. THESE WILL SLOWLY FADE AS THE EVENING CONTINUES. THURSDAY LOOKS LIKE ANOTHER UNSETTLED DAY...AS UPPER LOW MAKES IT/S CLOSEST PASS TO PA...TRACKING ACROSS UPSTATE NY...WITH THE 850MB LOW MOVING THROUGH PA. COOL TEMPS ALOFT...COMBINED WITH DIURNAL HEATING...SHOULD YIELD NUMEROUS SHRA AND TSRA BY THE AFTERNOON. HAVE CONTINUED POPS IN THE LIKELY CATEGORY BASED ON 12Z OPERATIONAL AND GEFS OUTPUT. DUE TO THE CHANGING POSITION AND TIMING OF THE LOW...HAVE SLIGHTLY LOWERED POPS ALONG THE SOUTHERN HALF OF THE CWA. THE SOUTHERLY LL JET AND PLUME OF HIGH PWATS WILL HAVE PASSED NE OF THE AREA THURSDAY...LIMITING THE THREAT OF ANY HVY RAINFALL. MODEL BLENDED QPF IS IN THE QUARTER TO HALF INCH RANGE THURSDAY. BEFORE THE LOW PASSES...TEMPS COULD REACH UP TO THE LOW 80S. AFTER THURSDAY/S NUMEROUS SHOWERS AND THE ADVECTION OF COOLER TEMPS ALOFT...HIGH TEMPS SHOULD DROP BELOW NORMAL FOR AUGUST...WITH MAXES MAINLY IN THE 70S THROUGH THE END OF THE WORK WEEK INTO THE WEEKEND. LATEST MED RANGE GUIDANCE POINTING TOWARD DRIER WX FRIDAY INTO EARLY NEXT WEEK...AS SUBTROPICAL HIGH IS PROGGED TO EDGE TOWARD THE REGION FROM THE MIDWEST. DAILY RING OF FIRE CONVECTION ON NE PERIPHERY OF THIS RIDGE WILL THREATEN WESTERN PA DURING THE FRI-SUN TIME FRAME...WHILE EASTERN PA IS LIKELY TO REMAIN DRY. DESPITE APPROACH OF UPPER RIDGE...NO BIG WARM UP EXPECTED...AS LARGE SFC HIGH OVR THE CANADIAN MARITIMES WILL CIRCULATE AN EASTERLY FLOW INTO CENTRAL PA. THERE MAY BE ISSUE WITH AM LOW CLOUDS/FOG DUE TO THE EXPECTED MOISTLY SERLY FLOW OVR THE AREA. && .AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
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AN ISOLATED SHOWER WILL BE POSSIBLE THROUGH 1 AM ACROSS SOUTH CENTRAL PA. MOST OF THE ACTIVITY IS OVER OH AND MOVING EAST. TOPS WERE COOLING...BUT NOW STORMS ARE WEAKENING SOME. MINOR CHANGES MADE ON THE 03Z PACKAGE. OTHERWISE THE MAIN CONCERN WILL BE MVFR AND IFR CONDITIONS LATE...GIVEN LIGHT WINDS...MAINLY CLEAR SKIES...AND DEWPOINTS HIGHER THAN WE HAVE SEEN THEM FOR MUCH OF THE SUMMER SEASON SO FAR. EXPECT THINGS TO IMPROVE WED MORNING...BUT THE REMAINS OF CONVECTION TO THE WEST AND THE UPPER LVL TROUGH MOVING IN WILL RESULT IN AT LEAST SOME SHOWERS. SOME THUNDERSTORMS WITH HEAVY RAIN WILL BE POSSIBLE. NOT A LOT OF CHANGE IN THE PATTERN BEFORE THE WEEKEND IF THEN. OUTLOOK... THU-SAT...MORNING FOG CHANCES EACH DAY. OVERALL VFR...BUT CHC OF MAINLY AFTERNOON SHRA/TSRA AND ASSOCIATED RESTRICTIONS. SUN...MAINLY VFR. STILL CHANCE OF SHRA IN THE MORNING.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LAMBERT NEAR TERM...LAMBERT SHORT TERM...GRUMM/LAMBERT LONG TERM...FITZGERALD/CERU AVIATION...MARTIN

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