Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 301916 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 316 PM EDT WED JUL 30 2014 .SYNOPSIS...
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UPPER LEVEL LOW PRESSURE WILL STAY ANCHORED OVER JAMES BAY CANADA THROUGH FRIDAY EVENING BEFORE WEAKENING AND MOVING TO THE NORTHEAST. ANOTHER TROUGH FORMING OVER THE LOWER OHIO VALLEY AND TRANSPORT A PLUME OF DEEP GULF AND WESTERN ATLANTIC MOISTURE NORTHWARD THIS WEEKEND...BRINGING NUMEROUS SHOWERS AND THUNDERSTORMS ACROSS THE SOUTHEASTERN HALF OF PENNSYLVANIA. TEMPERATURES WILL REMAIN COOLER THAN NORMALS.
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&& .NEAR TERM /THROUGH TONIGHT/...
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2 PM UPDATE... MU CAPE GRADUALLY INCREASING THROUGH THE EARLY AFTERNOON HOURS...AND HAS REACHED BETWEEN 500-1000 J/KG ACROSS THE NW HALF OF THE CWA AS OF 18Z. THIS WEAK TO MODERATE INSTABILITY /NEAR THE LEADING EDGE OF SLIGHTLY STEEPER MID LEVEL LAPSE RATES/ IS COMBINING WITH WEAK LARGE SCALE LIFT AHEAD OF AN APPROACHING UPPER LEVEL SHORT WAVE TO BRING A A FEW BKN LINES AND CLUSTERS OF SHOWERS AND ISOLATED LOW- TOPPED TSRA TO THE NW THIRD OF THE CWA SO FAR. ACROSS THE SE HALF OF THE STATE...SCATTERED/FLATTER CU AND MID LEVEL CLOUDS WERE NOTED...AS A RESULT OF WEAK WESTERLY ISENTROPIC UPGLIDE WITHIN THE 300-310K THETA LAYER. THE LOWER SUSQ VALLEY SHOULD STAY DRY RIGHT THROUGH THE REST OF THE DAYLIGHT HOURS BEFORE SOME WEAKENING SHOWERS DRIFT INTO THE AREA BETWEEN 00-04Z THURSDAY...AS THE LEADING EDGE OF THE POOL OF SLIGHTLY STEEPER MID LEVEL LAPSE /6-6.5C PER KM/ APPROACHES. TEMPS WILL RISE JUST ANOTHER 1-3 DEG F FOR THE REST OF THIS AFTERNOON...WITH HIGHS VARYING FROM THE MID AND UPPER 60S ACROSS THE NW MTNS...TO THE LOWER AND MID 70S IN THE CENTRAL VALLEYS...AND UPPER 70S TO AROUND 80F THROUGHOUT THE LOWER SUSQ VALLEY. THESE READINGS ARE STILL 6-9 DEGREES F BELOW NORMAL IN MOST LOCATIONS /ESPECIALLY ACROSS THE NW MTNS WHERE THE EARLIER DVLPMT OF THE CLOUD COVER HAS FLATTENED THE DIURNAL TEMP CURVE/.
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&& .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
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THE DIURNAL CONVECTION WILL SLIDE TO THE EAST ACROSS THE SUSQ VALLEY THIS EVENING WHILE FIZZLING OUT. THE COLD AIR ALOFT AND CYCLONIC FLOW WILL LIKELY KEEP A FEW /LOW TO MID/ CLOUD LAYERS AROUND THROUGH THE NIGHT /WITH A FEW SHOWERS POSSIBLE MAINLY ACROSS THE NW MTNS/. MIN TEMPS WILL BE CLOSER TO NORMAL TONIGHT...BUT SOME READINGS IN THE 40S ARE STILL POSSIBLE ACROSS THE NR MTNS REGION AND PERHAPS A FEW OF THE COLD SPOTS ACROSS THE HIGH TERRAIN OF SOMERSET COUNTY. THE UPPER LOW THROWS ONE MORE UPPERCUT AT NRN PENN THURSDAY MORNING...BEFORE REFUELING TEMPORARILY FOR A DAY OR SO ACROSS THE LOWER OHIO VALLEY. SCT/NMRS SHOWERS ARE EXPECTED TO AFFECT THE NRN THIRD TO HALF OF THE CWA IN THE MORNING. THE AFTERNOON SHOULD TURN OUT TO BE MAINLY DRY - WITHIN AN AREA OF LARGE SCALE SUBSIDENCE AND WEAK SFC HI PRESSURE IN THE WAKE OF THE UPPER WAVE. TEMPS ALOFT WILL STILL BE COOL AND DAYTIME INSTABILITY SHOULD BE GOOD ENOUGH FOR ISOLD-SCT SHOWERS IN THE WEST/NORTH DURING THE MID TO LATE AFTERNOON. HIGHS TEMPS THURSDAY MAY TRY TO SNEAK BACK TO NORMAL IN THE SE...BUT THE N/W ZONES WILL PROBABLY STILL BE 8-10 DEGS BELOW SEASONAL NORMALS GIVEN MORE IN THE WAY OF CLOUDS AND SCATTERED SHOWERS. THE THURSDAY NIGHT PERIOD CONTINUES TO LOOK LIKE THE LEAST LIKELY TIME FOR ANY SHOWERS TO DEVELOP WITH 500 MB HEIGHT RISE OF A FEW DAM...AND WEAK RIDGING OVER THE AREA AT THE SFC. LOWS EARLY FRIDAY MORNING WILL BE SIMILAR TO THE PREV FEW NIGHTS WITH SKIES TRYING TO CLEAR AND WINDS GENERALLY LIGHT/VARIABLE.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/... A DEEP UPPER LEVEL TROUGH WILL BE PRESENT ACROSS SOUTHEASTERN CANADA EARLY IN THE LONG TERM PERIOD...BUT WILL RELOAD WITH A SIGNIFICANT CHUNK ENERGY DIGGING INTO IT/S SW FLANK ACROSS THE MID MISS AND OHIO RIVER VALLEYS LATE THIS WEEK AND OVER THE UPCOMING WEEKEND /AS THE CANADIAN PORTION SHEARS OUT TO THE NE/. THIS POTENT SHORTWAVE TROUGH /AND AN ASSOCIATED WELL-DEFINED RIGHT ENTRANCE REGION OF A 90-95 KT 300 MB JET/ WILL LIFT NORTHEAST ACROSS THE MID ATLANTIC REGION FRIDAY THROUGH SUNDAY BEFORE SHIFTING TO THE SOUTHERN NEW ENGLAND COAST BY THE START OF NEXT WEEK. A SLOW MOVING /AND LIKELY STRENGTHENING/ BAROCLINIC ZONE... AND ONE OR MORE WAVES OF WEAK LOW PRESSURE MVG NE ALONG IT WILL BE LOCATED ACROSS CENTRAL OR ERN PENN DURING THIS 2-3 DAY PERIOD. PERIODS OF UNSETTLED WEATHER /SHOWERS AND TSTMS/ WILL OCCUR LATER FRIDAY...SATURDAY AND SUNDAY. THE STRENGTH OF THE LARGE SCALE FORCING AND INCREASINGLY ANOMALOUS HIGH PWAT AIR BENEATH THE NORTHWARD MIGRATING JET AND ITS THERMALLY DIRECT BRANCH WILL BRING THE POTENTIAL FOR SOME LOCALLY HEAVY/TRAINING SHOWERS AND TSRA... ESP ACROSS THE EASTERN HALF OF THE STATE/. MODEL DETAILS DIFFER SLIGHTLY WITH RESPECT TO THE TIMING AND LOCATION OF THE STRONGEST MESO/LARGER SCALE FORCING. BUT ALL GUIDANCE AGREES ON THE BASIC EVOLUTION AND NE MOVEMENT OF THIS TROUGH AND AXIS OF HIGH 40-50MM PWAT AIR RIDING NWD UP ALONG THE MID ATLANTIC PIEDMONT AND SPREADING ACROSS THE EASTERN HALF OF OUR CWA. AS A RESULT OF THESE TIMING/LOCATION DIFFERENCES...POPS WERE CAPPED OFF IN THE HIGH CHC CATEGORY. BUT AS THE FINER DETAILS UNFOLD WITH HIGHER RES MODEL GUIDANCE OVER THE NEXT FEW DAYS...POPS WILL UNDOUBTEDLY TREND HIGHER FOR SEVERAL PERIODS BETWEEN LATE FRIDAY AND SUNDAY. GRADUAL IMPROVEMENT WITH NEAR NORMAL TEMPS IS EXPECTED FOR EARLY NEXT WEEK. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
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INCREASING /BUT MAINLY VFR CLOUDS/ WILL OCCUR EAST OF THE I-99/ROUTE 22 CORRIDOR IN CENTRAL PENN AND THE SUSQ VALLEY THROUGH LATE THIS AFTERNOON. THE NW MTNS AND LAUREL HIGHLAND AIRFIELDS WILL SEE A DUAL LAYER OF STRATO CU AND ALTO CU CLOUDS WITH CONVECTIVE BASES AROUND 3-4 KFT AGL WITH THE MID LEVEL BASES AROUND 7 KFT AGL. THE APPROACH OF A WEAK COLD FRONT AND UPPER TROUGH WILL LEAD TO INCREASINGLY NUMEROUS SHOWERS /AND ISOLATED TSRA WITH BRIEF MVFR RESTRICTIONS POSSIBLE/ LATE THIS AFTERNOON AND EARLY THIS EVENING...MAINLY TO THE NW OF A LINE FROM KAOO TO KIPT. MAINLY VFR FOR TONIGHT WITH LINGERING BKN ALTO CU CLOUDS...AND PERHAPS A FEW STRAY LIGHT SHOWERS. A STRONGER 500 MB TROUGH WILL ROTATE ACROSS THE AREA ON THU...ACCOMPANIED BY ANOTHER ROUND OF SCTD SHOWERS AND STORMS /MAINLY ACROSS NRN PENN/. A BRIEF DRY PERIOD WITH WEAK RIDGING AT THE SFC AND ALOFT OVER THE REGIONAL AIRFIELDS THU NIGHT AND FRI. AFTERWARD...A POTENT UPPER TROUGH WILL FORM OVER THE LOWER OHIO VALLEY AND LIFT SLOWLY NE TWD THE MID ATL REGION OVER THE WEEKEND. DEEP MOISTURE SURGING NWD FROM THE GULF AND WRN ATLANTIC WILL BRING PERIODS OF SHOWERS AND TSRA OVER THE WEEKEND /FOCUSED ACROSS THE SE HALF OF THE STATE/. OUTLOOK... THU...SCT TSRA IMPACTS POSSIBLE. FRI-SUN...SCT PM TSRA IMPACTS POSSIBLE. MON-TUE...SLOW IMPROVEMENT EXPECTED WITH AREAS OF MVFR POSSIBLE MAINLY IN THE MORNING.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LAMBERT NEAR TERM...LAMBERT SHORT TERM...LAMBERT LONG TERM...LAMBERT/STEINBUGL AVIATION...LAMBERT

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