Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 191156 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 756 AM EDT TUE AUG 19 2014 .SYNOPSIS... AN UPPER LOW OVR THE W GRT LKS WILL DRIFT SLOWLY SE ACROSS UPSTATE NY AND NEW ENG BY LATE THIS WEEK. A LARGE SFC HIGH OVR THE CANADIAN MARITIMES WILL RIDGE SOUTHWARD INTO PA DURING THE UPCOMING WEEKEND AND EARLY NEXT WEEK. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... WEAK UPPER-LEVEL LOWS ARE STRUGGLING TO MAKE IT UNDER THE RETROGRADING UPPER LEVEL RIDGE. MODELS FOR DAYS NOW HAVE BEEN WETTER THAN REALITY. THE SREF AND GEFS ARE MORE ROBUST WITH SHOWER POTENTIAL TODAY THAN THE HIGH RESOLUTION CONVECTIVE FOLLOWING MODELS. LATEST 4KM NAM AND 3KM HRRR IMPLY SOME VERY ISOLATED CONVECTION ABOUT CENTRAL PA THIS AFTERNOON AND EARLY EVENING. NOTHING ORGANIZED OR SIGNIFICANT. SORT OF A QUANDARY HOW TO EFFECTIVELY USE THESE DATA VERSE THE LARGER SCALE MODELS WHERE CONVECTION IS GENERATED BY RELEASING INSTABILITY IN THE CONVECTIVE PARAMETERIZATION SCHEMES (CPS). BIASED POPS LOWER TOWARD CONVECTIVE ALLOWING MODELS THAT DO NOT USE CPS. MODELS IMPLY PARTLY TO MOSTLY CLOUDY TODAY. FIRST BATCH OF LOW CLOUDS IN SW PA WILL SHRINK AS IT ADVECTS ACROSS THE STATE. TEMPERATURE WISE CLOSE TO NORMAL. && .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... ANY SHOWER ACTIVITY THAT DEVELOPS SHOULD FADE FAST AROUND SUNSET. BUILDING 5940M RIDGE IN SOUTHERN US AND BLOCKING RIDGE TO OUR NORTH. WE ARE STUCK IN THE SQUEEZE PLAY BETWEEN THEM. AN ANEMIC FRONTAL SYSTEM TRIES TO PUSH THROUGH THE REGION. SREF LARGER SCALE MODELS SHOW SOME SURGE OF SLIGHTLY ABOVE NORMAL PW AND SOME CAPE INTO WESTERN PA. POPS SHOULD DROP OFF TO EAST AS THIS SYSTEM WILL WEAKEN AS IT MOVES BENEATH THE BLOCK. BEST CHANCE...AS MENTIONED BELOW FOR SEVERAL TENTHS WOULD BE IN WEST VERY LIGHT RAINFALL IN EASTERN AREAS. PREVIOUS: PASSAGE OF SHORTWAVE AND COOLING OF BLYR SHOULD CAUSE ANY EARLY EVENING SHOWERS TO DIMINISH SHORTLY AFTER SUNSET. HOWEVER...APPROACH OF UPPER LOW AND ASSOC LL JET/PLUME OF ANOMALOUS PWATS COULD SPREAD SHRA/TSRA INTO THE NW MTNS TOWARD DAWN WED. HAVE RAISED POPS MARKEDLY ACROSS THE AREA WED...AS MDLS NOW IN AGREEMENT WITH TIMING OF LL JET/PLUME OF ANOMALOUS PWATS. BLEND OF OPER AND ENSEMBLE GUIDANCE SUGGESTS MOST LIKELY RAINFALL WED WILL RANGE FROM LESS THAN 0.10 INCHES SE OF HARRISBURG...TO ARND A HALF INCH ACROSS WARREN CO. HOWEVER...MUCH HIGHER LOCALIZED AMTS ARE LIKELY ACROSS THE W MTNS...WHERE ENVIRONMENT OF MODERATE INSTABILITY AND HIGH PWATS WILL MAKE LOCALLY HVY TSRA POSSIBLE. CONVECTION- ALLOWING MDLS SUPPORT THIS SCENARIO WITH SPOT AMTS OF ARND 2 INCHES ON WED ACROSS THE W MTNS. A MORE STABLE MARITIME AIR MASS OVR EASTERN PA WILL MAKE TSRA UNLIKELY THERE. GEFS 925 TEMPS ARE SUPPORTIVE OF HIGH TEMPS WED FROM THE M70S OVR THE ALLEGHENY PLATEAU...TO THE L80S OVR THE SUSQ VALLEY. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... THURSDAY LOOKS LIKE ANOTHER UNSETTLED DAY...AS UPPER LOW MAKES IT/S CLOSEST PASS TO PA...TRACKING ACROSS UPSTATE NY. COOL TEMPS ALOFT...COMBINED WITH DIURNAL HEATING...SHOULD YIELD NUMEROUS SHRA AND TSRA BY AFTN. HAVE RAISED POPS TO THE LIKELY CATEGORY BASED ON 00Z OPER AND GEFS OUTPUT. SOUTHERLY LL JET AND PLUME OF HIGH PWATS WILL HAVE PASSED NE OF THE AREA THURSDAY...LIMITING THE THREAT OF ANY HVY RAINFALL. MDL BLENDED QPF IS IN THE QUARTER TO HALF INCH RANGE THURSDAY. THE NUMEROUS SHOWERS AND COOLER TEMPS ALOFT WILL RESULT IN HIGH TEMPS BLW NORMAL FOR AUGUST...WITH MAXES MAINLY IN THE 70S. 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 WARMUP 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 /12Z TUESDAY THROUGH SATURDAY/... VFR CONDITIONS WILL GIVE WAY TO FOG AND LOWERING VSBYS OVERNIGHT UNDER CLEAR SKIES AND LIGHT WINDS. EXPECT WIDESPREAD MVFR TO IFR VSBYS AND CIGS TO DEVELOP OVERNIGHT AT MOST CENTRAL AND NORTHERN AIRFIELDS. HOWEVER...HAVE NOT INCLUDED FOG IN THE LOWER SUSQUEHANNA TAFS OF KMDT AND KLNS...AS CONFIDENCE OF FORMATION IS LOWER. IF FOG DOES DEVELOP...LIKELY TO BE IN THE MVFR RANGE AT THESE LOCATIONS. CURRENT TIMING OF FOG IS FOR DEVELOPMENT AROUND 07Z IN MOST LOCATIONS...WITH THE DENSEST FOG BETWEEN 09Z AND 12Z. AFTER MORNING FOG...EXPECT GENERALLY VFR CONDITIONS. THERE IS A THREAT FOR SHRA/TSRA...MOST LIKELY IN THE SOUTHWEST AND LEAST LIKELY IN THE NORTHEAST. A VERY SLOW APPROACHING UPPER LOW WILL SLOWLY INCREASE CHANCES FOR DAILY SHOWERS AND POTENTIAL AFTERNOON TSRA FOR THE BALANCE OF THE WEEK. CURRENTLY...LATER WEDNESDAY AND THURSDAY LOOK LIKE THE HIGHEST LIKELIHOOD OF PRECIPITATION...WITH SURFACE FRONT CROSSING THE REGION. OUTLOOK... TUE...MORNING FOG...THEN MAINLY VFR...WITH SHRA/TSRA POSSIBLE. WED-FRI...MORNING FOG CHANCES EACH DAY. OVERALL VFR...BUT INCREASING CHANCES OF MAINLY AFTERNOON SHRA/TSRA AND ASSOCIATED RESTRICTIONS. SAT...MAINLY VFR. STILL CHANCE OF SHRA...BUT DECREASING CHANCES. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...FITZGERALD NEAR TERM...GRUMM SHORT TERM...GRUMM/FITZGERALD LONG TERM...FITZGERALD AVIATION...JUNG/GARTNER

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