Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 262120 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 420 PM EST THU FEB 26 2015 .SYNOPSIS... AN UPPER LEVEL TROUGH AND YET ANOTHER PUSH OF ARCTIC AIR WILL MOVE EAST ACROSS THE STATE LATE TODAY THROUGH EARLY FRIDAY... ACCOMPANIED BY MORE SNOW SHOWERS...WITH A SEVERAL HOUR PERIOD OF STEADY SNOW ACROSS THE LAUREL HIGHLANDS LATE TODAY AND THIS EVENING. A LARGE AREA OF HIGH PRESSURE WILL BUILD ACROSS THE AREA FOR THE FIRST PART OF THE WEEKEND. THE PATTERN WILL THEN BECOME RATHER STORMY WITH A FRONTAL BOUNDARY WAGGLING NORTH AND SOUTH OVER THE AREA INTO MID WEEK. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... APPROACHING UPPER LEVEL SHORT WAVE AND ANOTHER ARCTIC CFRONTAL BOUNDARY WILL BRING A FEW-SVRL HOUR PERIOD OF STEADY LIGHT SNOW TO THE LAURELS LATE THIS AFTERNOON AND EVENING...WHILE SOME INTERMITTENT LIGHTER SNOW AND SNOW SHOWERS DEVELOPS AND FALLS THROUGH EARLY TONIGHT TO THE EAST OF THE INTERSTATE 99/RT220 CORRIDOR. ACCUMS WILL RANGE FROM JUST A LIGHT COATING AT LOWER ELEVATIONS ACROSS THE SOUTHERN THIRD TO HALF OF THE CWA...TO BETWEEN 1 AND 2 INCHES ACROSS THE LAUREL HIGHLANDS. AS WINDS BACK AROUND FROM THE NORTH TO NW THROUGH TONIGHT...A BETTER LLVL UPSLOPE COMPONENT AND STEEPER LOW-MID LEVEL LAPSE RATES WILL MEAN THAT SNOW SHOWERS WILL CONTINUE ACROSS THE LAURELS...WHILE THE LIGHT SNOW EARLY ON...TRANSFORMS TO FLURRIES AND ISOLATED -SHSN TO THE SE OF THE ALLEGHENY FRONT. LOW TEMPS TONIGHT WILL RANGE FROM THE SINGLE DIGITS BELOW ZERO ACROSS THE NW MTNS...TO THE TEENS IN THE SE. THE GENERALLY LIGHT NORTH TO NW WIND WILL REDUCE THE APPARENT TEMP BY ABOUT 7-10F FROM THE ACTUAL AIR TEMPS. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... THE UPPER TROUGH AXIS FLATTENS OUT AN MOVES ACROSS THE REGION FRIDAY. AREAS OF STRATO CU AND ISOLATED TO SCTD MORNING SNOW SHOWERS WILL DISSOLVE AS ANOMALOUSLY STRONG 1040-1045 MB SFC HIGH PRESSURE BUILDS EAST INTO THE COMMONWEALTH FROM THE OHIO VALLEY. HIGH TEMPS FRIDAY WITH A WEST TO NW WIND OF 5-10KTS WILL VARY FROM JUST 8-12F ACROSS THE NW MTNS AND LAURELS...TO THE LOWER AND MID 20S ACROSS THE LOWER SUSQ VALLEY. CLEAR SKIES AND LIKELY THE COLDEST NIGHT UNTIL NEXT WINTER WILL OCCUR FRIDAY NIGHT AS THE CENTER OF HIGH PRESSURE MOVES OVER PENN. LOW TEMPS EARLY SATURDAY WILL BE 10-15F BELOW ZERO ACROSS THE WESTERN MTNS...AND 5 BELOW TO 5 ABOVE ELSEWHERE. THE COLDEST RURAL VALLEYS IN NW AND NCENT PENN COULD SEE THE MERCURY SETTLE TO AROUND -20F AT 11-12Z SATURDAY. && .LONG TERM /SATURDAY THROUGH THURSDAY/...
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A RELATIVELY MILD/ACTIVE SOUTHWEST FLOW ALOFT SHOULD PREVAIL THROUGH THE PERIOD AS THE PERSISTENT UPPER RIDGE OVER THE WRN U.S. TEMPORARILY BREAKS DOWN. AN ARCTIC HIGH PRESSURE SYSTEM OVER CENTRAL PA AT THE START OF THE PERIOD WILL RETREAT INTO ATLANTIC CANADA BY SUNDAY NIGHT. THE COMBINATION OF SHORTWAVE ENERGY IN THE SRN STREAM EJECTING FROM A DSW TROUGH AND A DIGGING NRN STREAM TROUGH MOVING SEWD FROM SOUTH CENTRAL CANADA TOWARD THE UPPER MIDWEST SEEMS TO DRIVE AN EXPANDING AREA OF WAA TYPE SNOWFALL SPREADING EASTWARD SUN-MON BEHIND THE SOUTHERLY RETURN FLOW INTO A RETREATING COLD SECTOR ASSOCD WITH THE DEPARTING ARCTIC HIGH. THE PCPN SHOULD BE ENHANCED ALONG AN EXPANDING BAROCLINIC ZONE ACROSS THE CENTRAL AND EASTERN US...AS UPPER RIDGING BUILDS OVER THE SE U.S. WHILE THERE APPEARS TO BE LITTLE INDICATION OF A STRONG SURFACE LOW...MODELS STILL GENERATE 0.25-0.50 INCH QPF AMTS ALONG THE BAROCLINIC ZONE. THERMAL PROFILES SEEM TO FAVOR SNOW ACROSS THE NW 1/2 OF CENTRAL PA WITH MIXED PTYPES IN THE SOUTH/SOUTHEAST. PRELIMINARY 24HR SNOW/ICE AMOUNTS WERE DERIVED USING A MULTI MODEL QPF BLEND WITH PSEUDO INTERNAL BIAS CORRECTION FACTOR AND WPC WWD. THIS RESULTS IN ADVY LEVEL SNOWFALL OVER THE NW 1/2 AND 0.10 INCH ICE/ZR OVER THE LWR SUSQ VLY. CONFIDENCE IN THE AMTS IS AVG AT BEST GIVEN UNCERTAINTY IN QPF AND LOW-LEVEL TEMPERATURES. THE LACK OF A DEFINED SFC CYCLONE ALSO RAISES SOME REG FLAGS. ANOTHER COLD HP SYSTEM BUILDS INTO THE REGION MON-TUE WITH ANOTHER SW FLOW WAA MSTR SURGE ALONG BAROCLINIC FRONTAL ZONE LKLY IMPACTING THE AREA INTO THE MIDDLE OF NEXT WEEK. TIMING DIFFERENCES ARE EVIDENT WITH THE GFS MORE BULLISH ON PCPN RETURNING EARLY TUE VS. SLOWER ECMWF (TUE NGT). MIXED PTYPE ISSUES ARE EXPECTED AGAIN WITH THIS NEXT SYSTEM.
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&& .AVIATION /21Z THURSDAY THROUGH TUESDAY/... EXPECT MAINLY VFR CLOUD BASES AND VSBYS ACROSS THE CENTRAL MTNS AND SUSQ VALLEY TAF SITES TO DIP ONCLY DOWN INTO THE MVFR RANGE AS AN UPPER LEVEL DISTURBANCE /AND ANOTHER PUSH OF ARCTIC AIR/ CROSSES THE REGION LATE TODAY AND EARLY TONIGHT WITH SCT-NUMEROUS -SHSN DEVELOPING IN THE 20-23Z PERIOD. MORE PERSISTENT MVFR CIGS AND VSBYS IN LIGHT SNOW WILL OCCUR ACROSS THE WESTERN MTNS...WITH PERIODS OF IFR LATE THIS AFTERNOON THROUGH EARLY TONIGHT. CONDITIONS WILL IMPROVE JUST A BIT AFTER MIDNIGHT TONIGHT ACROSS THE LAURELS...WITH MAINLY VFR VSBYS AND MVFR TO VFR CIGS DEVELOPING THROUGHOUT THE CENTRAL RIDGE AND VALLEY REGION AND SUSQ VALLEY. OUTLOOK... FRI...EARLY AM LGT SNOW/VIS REDUCTIONS POSSIBLE...OTHERWISE VFR WITH A 5-10KT WEST TO NW WIND. FRI NIGHT AND SAT...NO SIG WX EXPECTED. SUN...SNOW LIKELY NW MTNS. MIXED PRECIP POSSIBLE ELSEWHERE. MON...MIXED PRECIP WITH CIG/VIS REDUCTIONS POSSIBLE...MAINLY AM. && .CLIMATE... THE COLDEST FEBRUARY ON RECORD IS STILL LOOKING LIKELY. MONTHLY MEAN TEMPERATURES THROUGH THE 25TH...IPT 18.0...MDT 20.7. THE CURRENT RECORD COLDEST FEBRUARY..IPT 19.3...MDT 21.4 BOTH SET IN 1934. SO FAR...THIS MONTH IS THE THIRD COLDEST EVER AT IPT...AND FOURTH COLDEST EVER AT MDT. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DANGELO/LAMBERT NEAR TERM...LAMBERT SHORT TERM...LAMBERT LONG TERM...STEINBUGL AVIATION...LAMBERT CLIMATE...CTP

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