Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 200017 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 817 PM EDT FRI SEP 19 2014 .SYNOPSIS... GENERALLY FAIR WEATHER WILL BE INTERRUPTED FRIDAY NIGHT AND SATURDAY MORNING AS ATLANTIC MOISTURE POOLS OVER THE CENTRAL PA MOUNTAINS. A FRONTAL SYSTEM WILL BRING A CHANCE OF SHOWERS TO THE REGION ON SUNDAY...BEFORE ANOTHER LARGE AREA OF HIGH PRESSURE AND A BLOCKING UPPER-LEVEL RIDGE OVER CENTRAL CANADA BRINGS MORE FAIR AND COOL WEATHER FOR MOST OF NEXT WEEK. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... VIS SATL IMAGERY AND SFC OBS SHOW THAT LOW CLOUDS AND HAVE FOG DISSIPATED...WITH ABUNDANT SUNSHINE EXPECTED ACROSS CENTRAL PA INTO THE AFTERNOON HOURS. TEMPS SHOULD RESPOND NICELY...REACHING INTO 60S AND L70S. THESE VALUES ARE JUST A FEW DEGS BELOW NORMAL FOR THE BEGINNING OF FALL. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... HIGH PRESSURE MOVING OFF THE NEW ENGLAND COAST TONIGHT WILL FORCE A LONG-FETCH OFF THE ATLANTIC TO ASCEND THE MOUNTAINS OF CENTRAL PA. THIS SHOULD CREATE A BLANKET OF CLOUDS AND DRIZZLE/FOG AS IT SETTLES IN THROUGH THE NIGHT. BUT...THE WINDS CONTINUE TO VEER ON SATURDAY AND SHOULD ALLEVIATE THE LOW-CLOUD PROBLEM LATE IN THE MORNING AND EARLY AFTERNOON ON SATURDAY. OVERNIGHT MINS WILL LIKELY BE A TOUCH ABOVE NORMAL...BUT WITH THE EXPECTED INCREASE IN SUNSHINE THROUGH THE DAY...MAXES WILL TRY TO RUN UP INTO THE 70S FOR MOST PLACES - ESP IN THE VALLEYS OF THE SE WHERE THERE SHOULD BE LESS CLOUD COVER. WILL HOLD THE TEMPS AROUND 70F ALONG THE SPINE OF THE MOUNTAINS WHERE THE CLOUDS WILL TAKE LONGEST TO BREAK. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... ALL OF THE GUIDANCE SHOWS A FRONTAL SYSTEM MOVING NORTHWEST TO SOUTHEAST ACROSS THE STATE OVERNIGHT SATURDAY INTO SUNDAY EVENING. THIS IS MOST LIKELY THE ONLY RAIN EVENT THAT SHOULD AFFECT THE REGION OF THE NEXT 7-12 DAYS AS A BLOCKING 500 HPA RIDGE WITH OVER 2 SIGMA HEIGHT ANOMALIES SHOULD PROVIDE A PROLONGED PERIOD OF DRY WEATHER. AT THIS TIME THE MODELS AND ENSEMBLES ALL IMPLY AN INCREASE IN SHOWER ACTIVITY AFTER MIDNIGHT NORTHWESTERN PENNSYLVANIA AND TOWARD SUNRISE IN CENTRAL AREAS EARLY MORNING. THE GEFS AND SREF BOTH IMPLY THE 12 HOUR PERIOD FOR THE BEST RAINFALL WILL BE BETWEEN ABOUT 8 AM AND 8 PM SUNDAY. THE RAINFALL LINGERS IN THE ENSEMBLE PDF UNTIL BETWEEN 8 AND 2 AM SUNDAY NIGHT INTO MONDAY IN THE EAST. THE RAPIDLY LOWERING PW FIELD IMPLIES ALL RAIN GONE IN EAST AFTER MIDNIGHT SUNDAY. AT THIS TIME THE HIGHER POPS AND HIGHER QPFS SHOULD BE IN THE NORTHERN AREAS. FEW MEMBERS OF ANY EFS SHOW MUCH MORE THAN 0.25 INCHES WITH PERHAPS 40 PERCENT SHOWING 0.50 INCHES IN THE NORTHERN AREAS. MOST QPFS IMPLY A 0.10 TO 0.20 INCH RAINFALL EVENT. KIND OF ANEMIC. DID MENTION THUNDERSTORMS AS THERE IS A WARM SURGE AND SOME HINTS OF MODEST CAPE IN THE HIGHER RESOLUTION MODELS AND EFS PERHAPS 600 TO 800JKG-1. LOWER IN THE GEFS. A FEW THUNDERSTORMS COULD BOOST QPFS UP A BIT IF THEY APPEAR. HIGH PRESSURE BUILDS IN MONDAY BEHIND THE FRONT AND SORT OF PARKS ITSELF OVER NEW YORK AND NEW ENGLAND WITH +2 TO +3 SIGMA ABOVE NORMAL MSLP ANOMALIES BY WEDNESDAY-THURSDAY. HIGH CONFIDENCE IN THIS FORECAST AS THE MODELS ALL SHOW A BLOCKING 500 HPA ANTICYCLONE TO THE NORTHWEST AS A MASSIVE 500 HPA POSITIVE HEIGHT ANOMALY OF +2 TO +3 SIGMA DEVELOPS OVER CENTRAL CANADA BY THURSDAY AND INTO FRIDAY. OUR MODELS AND EFS DO WELL FORECASTING ANTICYCLONES. SO I AM HIGH ON THE FAIR WEATHER FORECAST NEXT WEEK. ONLY FUN ISSUES ARE HOW MUCH RAIN SUNDAY AND HOW SUNNY WILL IT GET BEHIND THE FRONT MONDAY. DID NOT ATTEMPT TO DRAW THE DIURNAL FOG AND LOW CLOUDS LIKELY TO AFFECT THE REGION ONCE THE BIG HIGH TAKES HOLD. THIS WILL BE A NEARLY IDEAL DIURNAL FOG PATTERN WED-SUNDAY. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... MOIST SERLY FLOW OFF OF THE ATLANTIC...COMBINED WITH OROGRAPHIC LIFT AND COOLING BLYR...IS CAUSING STRATO-CU TO EXPAND ACROSS CENTRAL PA THIS EVENING. AT 00Z...CIGS ARE GENERALLY IN THE 5-7KFT RANGE. HOWEVER...MODEST RADIATIONAL COOLING OF BLYR WILL CAUSE CIGS TO LOWER OVERNIGHT. LATEST MDL SOUNDINGS SUGGEST ALL SITES WILL REMAIN VFR THROUGH ABOUT 04-06Z BEFORE CONDS DETERIORATE TO MVFR/IFR. A GRADUAL WIND SHIFT FROM SE TO SOUTH OVERNIGHT WILL FAVOR THE N MTNS FOR THE BEST OROGRAPHIC LIFT AND HIGHEST CHANCE OF IFR CIGS. FURTHER SOUTH...CONFIDENCE IN IFR CONDS LATE TONIGHT IS NOT VERY HIGH. CONDITIONAL CLIMATOLOGY AND LATEST SREF OUTPUT SUGGEST MVFR CIGS MORE LIKELY LATE TONIGHT ACROSS CENTRAL AND SOUTHERN PA...DESPITE THE MORE PESSIMISTIC MOS GUIDANCE. EARLY LOW CLOUDS SHOULD MIX OUT BY LATE AM. MDL DATA THEN SUPPORTS A HIGH CONFIDENCE OF VFR CONDS DURING THE AFTN AND EVENING...AS HIGH PRES RIDGE REMAINS OVR THE AREA. OUTLOOK... SUN...AM FOG POSSIBLE EASTERN PA. SLIGHT CHC OF PM TSRA IMPACTS W MTNS. MON...AM LOW CIGS POSS W MTNS. TUE-WED...NO SIG WX EXPECTED. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...GRUMM/LA CORTE/GARTNER NEAR TERM...LA CORTE/GARTNER SHORT TERM...DANGELO/GARTNER LONG TERM...GRUMM AVIATION...FITZGERALD

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