Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 031627 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1227 PM EDT MON AUG 3 2015 .SYNOPSIS... A LARGE UPPER LOW CENTERED OVER NORTHERN ONTARIO WILL TRANSLATE EASTWARD OVER THE NEXT FEW DAYS. IT WILL DRIVE A COLD FRONT THROUGH THE STATE TODAY AND EARLY TONIGHT. LARGELY CONFLUENT NORTHWEST FLOW ALOFT OVER THE GREAT LAKES DURING THE MID WEEK WILL HELP HIGH PRESSURE SETTLE IN BEHIND THE FRONT. HOWEVER...THE FRONT WILL HANG UP JUST TO THE SOUTH OF THE REGION AND MAY RETURN NORTHWARD AS A WARM FRONT LATER THIS WEEK. && .NEAR TERM /UNTIL 8 PM THIS EVENING/...
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WAITING GAME IS ON FOR CONVECTION TO BEGIN FIRING OVER THE NEXT SEVERAL HOURS IN THE MODERATELY UNSTABLE/MDTLY SHEARED ENVIRONMENT OVER CENTRAL PENN. AN AREA OF CONVECTIVE DEBRIS/LAYERED MID AND HIGH CLOUDS WILL CONTINUE TO SLOWLY DISSOLVE AS IT DRIFTS EAST AT 20-25 KTS ACROSS THE CENTRAL AND EASTERN PART OF THE CWA THROUGH THE AFTERNOON HOURS. IT APPEARS THAT HIGH RES MODELS /4 KM WRF...AND HRRR - HRRRX/ ARE LATCHING ONTO THE WESTERN PERIPHERY OF THIS MID/HIGH CLOUD DECK TO ACT AS A DECENT BOUNDARY FOR DIFFERENTIAL HEATING...AND LLVL CONVERGENCE /AS A RESULT OF DEEPER VERTICAL MIXING OF WESTERLY MOMENTUM OCCURS IN THE CLEARING SKIES OVER THE WESTERN HIGH TERRAIN/. SUNSHINE THROUGH THINNING HIGH CLOUDS ACROSS NWRN PENN WILL COMBINE WITH AN APPROACHING CFRONT TO TRIGGER ANOTHER LINE OR TWO OF STG TO POTENTIALLY SEVERE TSRA ACROSS NRN OHIO AND NEAR THE LAKE ERIE BREEZE BOUNDARY IN FAR NWRN PENN. LIGHT SOUTHWEST WINDS AT THE SFC WILL VEER A BIT THROUGH THE DAY AS THE COLD FRONT NEARS. THE FRONT THEN WASHES OUT AND WILL BE TOUGH TO DISCRIMINATE THIS AFTERNOON AND EVENING. SPC DAY ONE OUTLOOK KEEPS THE SLIGHT RISK OVER ALMOST ALL OF CENTRAL PA. THE EXCEPTION IS THE FAR SERN COS. THIS IS PRESUMABLY DUE TO THE LOSS OF CAPE AS THE HEAT OF THE DAY GOES AWAY. HOWEVER...THE MIXED LAYER CAPES OF 1-2K JOULES AND GOOD DEEP LAYER SHEAR MAKE FOR AN ENVIRONMENT WHERE STORMS WILL GROW TALL AND MOVE FAIRLY QUICKLY W-E. 0-3KM BULK SHEAR WILL INCREASE TO 30-35 KTS...WITH 0-6KM VALUES ABOUT 10 KTS FASTER. THE MAIN SEVERE WEATHER THREAT SHOULD BE SEVERAL...EMBEDDED ORGANIZED BOWS WITHIN THE FEW BKN LINES OF SHOWERS/TSRA...CONSIDERING THE NEARLY UNI-DIRECTIONAL VERTICAL WIND PROFILE. IN ADDITION...DOWNDRAFT CAPE PER SPC MESO ANALYSIS PAGE HAS INCREASED TO 1000-1200 J/KG ACROSS ROUGHLY THE SERN HALF OF THE CWA AT 16Z. MARGINALLY LARGE HAIL IS THE SECONDARY SEVERE THREAT IN THIS CASE. HEAVY RAIN DOES NOT SEEM TO POSE A THREAT TODAY WITHOUT SLOW- MOVING STORMS OR MUCH POTENTIAL FOR BACK-BUILDING. SUNSHINE WITH HELP FROM A WEST/DOWNSLOPE SFC WIND WILL HELP THE MAXES TOUCH 90 IN THE SERN THIRD OF THE AREA. AFTERNOON DEWPOINTS IN THE UPPER 50S AND LOWER 60S WILL KEEP HEAT-RELATED FLAGS ON THE SHELF TODAY.
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&& .SHORT TERM /8 PM THIS EVENING THROUGH 6 PM TUESDAY/...
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MOST LIKELY...A BROKEN ASSORTMENT OF STORMS WILL BE ON-GOING AT THE START OF THE SHORT-TERM. SOME ORGANIZATION FROM MULTI-CELL CLUSTERS TO BOWING SEGMENTS SHOULD EMERGE DUE TO THE UNI-DIR WIND PROFILE. THE CURRENT CROP OF MESO MDLS HAS A POOR LEVEL OF CONTINUITY AMONG THEM WHEN IT COMES TO HOW LONG CONVECTION WILL LAST AND WHEN THE ALL-CLEAR WILL SOUND. THE COLD FRONT CURRENTLY ACROSS THE LOWER LAKES WILL MOVE INTO THE STATE LATER TODAY...BUT GETS LOST IN THE DISTURBANCES IN THE P-FILED CAUSED BY CONVECTIVE COLD POOLS. HOWEVER...BY MIDNIGHT THE FRONT SHOULD START TO EMERGE OVER THE EASTERN END OF THE STATE. WILL KEEP POPS IN THE LIKELY RANGE CONSIDERING THE UNCERTAINTY OF WHERE THE CONVECTION WILL OCCUR. LOWS WILL GET INTO THE 50S IN THE NW BUT FOG MAY NOT BE A PROBLEM DUE TO SOME AIR MOVEMENT. THIS USUALLY SPELLS LOW CLOUDS INSTEAD OF FOG. TUESDAY SEEMS LIKE A DRY DAY AS HIGH PRESSURE BUILDS IN. BUT... THE HEATING COULD AGAIN POP AN ISOLATED SHOWER IN THE NRN MTNS AND PERHAPS THE LAURELS. THE COVERAGE OF ANYTHING WHICH WOULD MAKE PRECIP REACH THE GROUND IS GOING TO BE WIDELY SCT. HAVE HELD ONTO THE IDEA OF A LOW POP IN THE FAR SE AS WELL SINCE THE FRONT SHOULD NOT MOVE TOO FAR AWAY. MAXES IN THE 70S NW HALF AND 80S SE HALF. NOT TOO FAR OFF NORMALS FOR LATE SUMMER.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... THE UPPER LOW OVER NORTHERN QUEBEC SHOULD CONTINUE TO DRIFT TO THE NORTHEAST AND ZONAL TO SLIGHTLY NORTHWEST FLOW IS EXPECTED TO FOLLOW AS A QUASI-STATIONARY BOUNDARY HANGS OUT JUST TO THE SOUTH OF THE STATE. EARLIER RUNS OF THE GFS/EC HAD MOVED THE BOUNDARY FURTHER NORTH BUT THEY HAVE RETURNED SOUTHWARD A BIT WITH THIS PACKAGE. UNCERTAINTY IN THE PLACEMENT OF THE BOUNDARY WILL KEEP SOME POP IN THE SRN PART OF THE STATE...BUT MOST LOCATIONS WILL BE DRY UNTIL WED NIGHT OR THURS. THEN A STACKED LOW WILL SLIDE EASTWARD FROM THE MID MISSISSIPPI VALLEY AND MAY MAKE A MORE-OR- LESS CONSTANT RAIN INSTEAD OF SHOWERY/CONVECTIVE PRECIP. THE UPPER LEVEL LOW WILL FINALLY MOVE OFF NEXT WEEKEND WHICH WILL BE A HERALD FOR QUIETER WEATHER. TEMPERATURES SHOULD TREND COOLER LATER IN THE WEEK. && .AVIATION /16Z MONDAY THROUGH FRIDAY/...
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AN APPROACHING COLD FRONT AND PRECEDING SFC/LEE TROUGH DEVELOPING ACROSS CENTRAL PENN WILL ACT AS TWO AREAS OF FOCUS FOR LATE AFTERNOON/EVENING SHRA TSRA WITH SCT/BRIEF MVFR CIGS AND VSBYS. A FEW OF THE STORMS MAY BE STRONG TO SEVERE...WITH VERY BRIEF IFR VSBY IN +RA AND HIGHLY-LOCALIZED WESTERLY SFC WIND GUSTS AOA 40KTS. WILL CONTINUE TO USE -SHRA WITH VCTS BTWN 18-22Z TO SHOW TSTM IMPACT RISK AT ALL TERMINALS. OUTLOOK... TUE...VFR. VERY ISOLD P.M. SHRA PSBL XTRME NRN AIRSPACE. WED...VFR. NO SIG WX. THU-FRI...VFR/MVFR WITH RAIN PSBL AS LOW PRES TRACKS SOUTH OF CENTRAL PA.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LAMBERT NEAR TERM...LAMBERT/DANGELO SHORT TERM...DANGELO LONG TERM...DANGELO/CERU AVIATION...LAMBERT/GARTNER

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