Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 061427 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1027 AM EDT MON JUL 6 2015 .SYNOPSIS...
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A WEAKENING WAVE OF LOW PRESSURE WILL MOVE THROUGH THE REGION TODAY. A COLD FRONT WILL MOVE INTO THE AREA TUESDAY NIGHT...AND STALL ALONG JUST SOUTH OF THE MASON DIXON LINE FOR MIDWEEK.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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LATEST RADAR SHOWS WIDELY SCATTERED SHOWERS MOVING NORTH INTO THE CENTRAL MOUNTAINS. SHOWERS ARE STILL SMALL ENOUGH TO NOT BE CAUSING ANY LIGHTNING. A SHEARING OUT UPPER LOW/TROUGH WILL BRING A SURGE OF ANOMALOUSLY HIGH PWATS INTO THE FORECAST AREA DURING THE DAY TODAY. MODELS SHOW INCREASING INSTABILITY WITH THE APPROACH OF THE UPPER SYSTEM AND MOISTURE. WITH MODEST HEATING IT LOOKS REASONABLE TO SEE SHOWERS AND THUNDERSTORMS BECOME MORE NUMEROUS AS WE MOVE DEEPER INTO THE DAY. HAVE CONTINUED TO LEAN CLOSER TO SREF AND GEFS POPS...WHICH SUPPORT CATEGORICAL SHOWERS OVER MUCH OF CENTRAL PA. MODEL BLENDED QPF OF A .25" TO .50" INCH SEEMS REASONABLE FOR BASIN AVERAGE AMOUNTS. HOWEVER ...CONVECTION-ALLOWING MODELS IMPLY LOCALIZED HEAVIER AMOUNTS IN PLACES THAT SEE A FEW TRAINING TSRA. GIVEN THE WET GROUND AND 1HR FFG VALUES LESS THAN AN INCH OVER MUCH OF CENTRAL PA...WILL MAINTAIN THE MENTION OF LOCAL FLOODING IN THE HWO. BEST CHC OF LOCALLY EXCESSIVE RAINFALL SHOULD BE ACROSS THE WESTERN AND SOUTHERN COUNTIES...WHERE MODEL INSTABILITY IS GREATEST. WEAK FLOW ALOFT AND PRACTICALLY NON- EXISTENT DCAPE DUE TO LACK OF MID LVL DRY AIR SIGNALS A LOW CHC OF SVR WEATHER. GREATER PROBABILITY FOR HIGH CAPE /EXCEEDING 2000 J/KG/ EXISTS ACROSS THE LOWER SUSQ VALLEYS AND ADJACENT COMMUNITIES THIS AFTERNOON AND EARLY THIS EVENING. SPC HAS ACCOUNTED FOR THIS AREA OF LOCALLY HIGH PRECIP POTENTIAL...INSTABILITY...AND WEAK TO MDT SOUTHERLY LLVL SHEAR BY PLACING SCENT PENN AND ADJACENT PORTIONS OF THE LOWER SUSQ VALLEY UNDER A MARGINAL RISK FOR SVR TSRA LATE THIS AFTERNOON INTO THIS EVENING. HIGHS THIS AFTERNOON /IN THE INCREASING MUGGINESS/ WILL BE IN THE MID 70S ACROSS THE LAUREL HIGHLANDS AND U70S TO NEAR 80F ELSEWHERE. DEWPOINTS ARE PROGGED TO CREEP INTO THE UNCOMFORTABLE RANGE BTWN 65-70F.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/... THE HEART OF A VERY WARM AND MUGGY AIRMASS WILL BE OVER THE STATE TONIGHT AND TUESDAY WITH MAINLY RAIN-FREE CONDITIONS BETWEEN 04-20Z TUESDAY. LATER TUESDAY AFTERNOON ISOLATED TO SCATTERED CONVECTION WILL FORM INVOF A LEE TROUGH...AND IN ADVANCE OF A SFC COLD FRONT APPROACHING FROM THE OHIO VALLEY. MUCH OF THE ENERGY PUSHING THIS FRONT EASTWARD APPEARS THAT IT/LL BE SHEARING OFF TO THE ENE ACROSS SRN ONTARIO AND QUEBEC. STILL A CLOSE CALL ENOUGH CALL FOR ADEQUATE DEEP-LAYER SHEAR TO BRING SCATTERED SHOWERS...AND ISOLATED STRONG TO POSSIBLY SVR TSRA /MAINLY ACROSS THE WEST/ LATE IN THE DAY TUESDAY AND TUESDAY NIGHT. WARMING TEMPS IN THE MID LEVELS /FROM 7C...UP TO 9C TUESDAY AFTERNOON AND EVENING/ WILL HELP TO GREATLY LIMIT/CAP OFF SHOWERS AND TSRA ACROSS MUCH OF CENTRAL PENN AND THE SUSQ VALLEY. HIGH TUESDAY WILL LIKELY BE THE WARMEST THIS WEEK...AND ABOUT 3-4 DEG F ABOVE NORMAL. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... THE 07/00Z MODEL AND ENSEMBLE GUIDANCE IS PROVIDING A FAIRLY CONSISTENT SIGNAL THAT THE AREA WILL REMAIN IN A LOW AMPLITUDE QUASI-ZONAL MID/UPPER FLOW PATTERN WITHIN THE NORTHERN STREAM WESTERLIES. AS MIGHT BE EXPECTED IN THIS PATTERN...THERE IS LOW PREDICTABILITY/CONFIDENCE GIVEN DEGREE OF SPREAD AND MEANINGFUL DIFFERENCES ASSOCIATED WITH SHORTWAVE DETAILS. THIS LARGELY UNSETTLED AND RECENTLY PERSISTENT WEATHER PATTERN FOR THE LOCAL AREA WILL BE MODULATED TO SOME EXTENT BY RETROGRESSION OF UNSEASONABLY STRONG UPPER TROUGH/RIDGE COUPLET OFF THE WEST COAST AND OVER THE SOUTHEAST AND SCENTRL U.S. THERE IS BROAD SUPPORT FOR ANOTHER MEAN TROUGH TO DEVELOP OVER THE NORTHEAST/MID ATLANTIC STATES BY NEXT WEEK/JULY 13TH AS ENERGY EJECTING FROM CA UPPER LOW EVOLVES DOWNSTREAM IN THE WESTERLIES AND TEAMS WITH VORTEX OVER HUDSON BAY. IN TERMS OF SENSIBLE WEATHER...A WELL-DEFINED COLD FRONT ENTERS CENTRAL PA EARLY WEDNESDAY ACCOMPANIED BY SHOWERS/TSTMS...THEN BECOMES WAVY AS IT STALLS OUT FROM NEAR THE OH RIVER/MASON DIXON LINE. EXPECT ONE OR MORE EPISODES OF PCPN THRU LATE WEEK MOST LKLY DUE TO MCS REMNANTS OR CONVECTIVELY INDUCED LOWS TRACKING EWD FROM THE MID MS/OH VLY...BUT TOO DIFFICULT TO PIN POINT TIMING/LOCATION AT THIS POINT. FWIW THE MODEL BIAS IS USUALLY TOO FAR NORTH WITH MCS ACTIVITY. PCPN RISK SHOULD EVENTUALLY BE ENHANCED TOWARD THE END OF THE PERIOD INTO EARLY NEXT WEEK AS CA LOW ENERGY AND ASSOCIATED SFC SYSTEM REACHES THE GREAT LAKES. WHAT WE CAN SAY WITH RELATIVE CERTAINTY IS THAT WE DO NOT EXPECT ANY HEAT WAVES OR EXTENDED PERIODS OF DRY WEATHER OVER THE NEXT 7+ DAYS. && .AVIATION /14Z MONDAY THROUGH FRIDAY/...
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WIDESPREAD MVFR/IFR CONDITIONS HAVE DEVELOPED IN THE HUMID AIRMASS AHEAD OF THE APPROACHING STORM SYSTEM MOVING OUT OF THE OHIO VALLEY. EXPECT SHOWER ACTIVITY TO INCREASE IN COVERAGE AND SPREAD FROM SOUTH TO NORTH THROUGH THE AFTERNOON. SHOWERS WILL TEND TO BE SLOW-MOVG AND COULD PRODUCE HEAVY DOWNPOURS AND LCL IFR VISBYS. THE UPPER LOW WILL WEAKEN OVER CENTRAL PA INTO TNGT BUT STILL MAINTAIN SCT SHOWER RISK...THEREFORE SIMPLY WENT WITH VCSH AFT 00Z. CIGS/VSBYS SHOULD TREND GRADUALLY LOWER OVERNIGHT GIVEN DIURNAL COOLING...HIGH LOW LEVEL MSTR/NARROW T-TD SPREADS AND LGT WINDS...WITH AT LEAST MARGINAL RESTRICTIONS LKLY AT SEVERAL SITES INTO EARLY TUESDAY. LOWER CONDITIONS TUESDAY MORNING SHOULD IMPROVE BY AFTN. A COLD FRONT WILL APPROACH THE AIRSPACE FROM THE LWR LKS/OH VLY BY LATE IN THE DAY AND SHIFT SLOWLY SEWD INTO THE AIRSPACE TUE NGT/WED BEFORE STALLING OUT NEAR PA/MD BORDER THURS INTO FRIDAY. OUTLOOK... TUE-FRI...VFR/MVFR WITH PERIODS OF SHRA/AFTN TSTMS.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LA CORTE/LAMBERT NEAR TERM...LA CORTE/LAMBERT SHORT TERM...LAMBERT LONG TERM...STEINBUGL AVIATION...LA CORTE/STEINBUGL

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