Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 031648 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1148 AM EST TUE MAR 3 2015 .SYNOPSIS... AN AREA OF LOW PRESSURE OVER THE CENTRAL PLAINS STATES WILL MOVE QUICKLY NORTHEAST TO THE UPPER GREAT LAKES BY TONIGHT. A SURGE OF DEEP MOISTURE AHEAD OF THIS LOW WILL RIDE UP AN OVER THE COLD AIR IN PLACE ACROSS PENNSYLVANIA AND LEAD TO ANOTHER ROUND OF SIGNIFICANT WINTRY/MIXED PRECIPITATION THIS AFTERNOON INTO EARLY TONIGHT. THE PRECIPITATION WILL LIKELY TURN TO RAIN ACROSS SOUTHERN SECTIONS EARLY WEDNESDAY. COLDER TEMPERATURES WILL FOLLOW FOR THE LATTER PART OF THE WEEK...AND STEADY SNOW WILL RETURN WEDNESDAY EVENING INTO THURSDAY AS A WAVE OF LOW PRESSURE RIPPLES ALONG A NEARLY STATIONARY FRONT THAT WILL BE DRAPED JUST TO OUR SOUTH. HIGH PRESSURE AND COLD AIR WILL RETURN FOR FRIDAY INTO THE FIRST PART OF THE WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... AT MIDDAY...PRIMARY BURST OF WARM ADVECTION IS MAINTAINING/PROPOGATING A MODERATE BAND OF SNOW EXTENDING FROM THE NORTHWEST MOUNTAINS TO THE LOWER SUSQ RIVER VALLEY...WITH A LARGE DRY SLOT OVER SOUTHEAST OHIO AND SOUTHWEST PA FILLING IN WITH MORE SHOWERY ELEMENTS. TEMPERATURES OVER SOMERSET COUNTY RANG FROM THE LOWER 20S NORTH TO THE UPPER 20S SOUTH WITHIN THIS DRY SLOT. SUBSEQUENT PRECIP SHOULD BE MIX TO FZRA THIS AFTERNOON. THE REST OF THE SOUTHERN THIRD OF CENTRAL PA WILL SEE A SEVERAL HOUR LULL IN PRECIP EARLY TO MID AFTERNOON AS A RESULT OF THIS DRY SLOT...AFTER THE INITIAL WAA BAND CROSSES. ACROSS THE NORTHERN HALF OF CENTRAL PA...TRANSITIONS TO SLEET AND THEN FREEZING RAIN WILL TAKE PLACE MID TO LATE AFTERNOON. NEAR TERM DETAILS APPEAR TO BE IN GOOD SHAPE...BUT STILL CONCERNED THAT WE`LL EXCEED ADVISORY CRITERIA FOR ICE LATER TONIGHT NORTH OF INTERSATE 80. ADJUSTED ICE AMOUNTS UPWARD BY SEVERAL HUNDRETHS ALONG AND NORTH OF I80 WHICH KEEPS AMOUNTS WITHIN ADVISORY CRITERIA. 06Z SREF THREATS BACKED OFF ON EARLIER ROBUST AMOUNTS AND PERCENTAGES...BUT PREVIOUS THREATS HAD INDICATED 70-80% CONFIDENCE IN .20-.30" OR MORE OF ICE. SUCCESSIVE HRRR RUNS CONTINUE TO DELAY WARMING AT THE END OF ITS 15-HOUR WINDOW...MEANING THAT MUCH OF NORTH CENTRAL PA WILL LIKELY NEVER RISE ABOVE FREEZING. CRITICAL TIMEFRAME WILL BE BETWEEN 21Z AND 04Z...AND THINK IT WILL BE A WHITES OF THEIR EYES DECISION FOR THE EVENING SHFIT BASED ON RADAR EVOLUTION AND ADJUSTMENTS OF HRW-ARW AND HRRR CONSENSUS LATE THIS AFTERNOON. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... PROLONGED ICE ACCRETION IS THE MAIN THREAT TONIGHT THROUGHOUT THE CENTRAL AND NRN MTNS OF THE STATE /AND TO A LESSER DEGREE ACROSS THE MID AND LOWER SUSQ VALLEY/...PRECEDED BY THE COATING TO 1 INCH OF SNOW FAR SOUTH AND 1 TO 2 INCHES OF SNOW IN MOST AREAS (WITH UP TO 3 INCHES NORTH). THE NORTH MAY NOT COMPLETELY MIX OUT THE SHALLOW AND INITIALLY BITTERLY COLD AIR...SO EXPECT AREAS OF FREEZING RAIN TO PERSIST THERE THROUGH THE PRE DAWN HOURS ON WEDNESDAY. ICE ACCUMS SHOULD BE ON THE ORDER OF 0.10-0.20 OF AN INCH ACROSS THE NCENT MTNS OF PA...WITH LESSER AMOUNTS IN MOST PLACES TO THE SOUTH OF INTERSTATE 80. WINTER WEATHER ADVISORIES CONTINUE FOR A PERIOD OF SNOW/SLEET ACCUM...FOLLOWED BY FREEZING RAIN...THIS AFTERNOON THROUGH THE EARLY MORNING HOURS ON WEDNESDAY. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... AN ACTIVE LATE-WINTER PATTERN WILL AFFECT CENTRAL PA THROUGH MIDWEEK FOLLOWED BY WHAT IS HOPEFULLY THE LAST SHOT OF ARCTIC AIR FOR THE SEASON THURSDAY INTO FRIDAY. THE PATTERN SHOULD DRY OUT LATE IN THE WEEK THROUGH THE UPCOMING WEEKEND WITH HIGH PRESSURE IN CONTROL MOST OF THE TIME. THE GENERAL MODEL CONSENSUS IS TO MAINTAIN A RIDGE IN THE WEST AND TROUGH IN THE EAST...LIMITING TEMPERATURE MODERATIONS TO NO BETTER THAN CLIMATE NORMALS. MODELS SHOW AN ACTIVE PCPN ZONE EXTENDING FROM THE SRN PLAINS ENEWD INTO THE NRN MID ATLANTIC STATES...IN BTWN A POSITIVELY TILTED TROUGH PUSHING THROUGH THE PLAINS/MIDWEST/GREAT LAKES AND ABOVE NORMAL RIDGING FROM THE GOMEX INTO THE WRN ATLANTIC OCEAN. SEVERAL WAVES OF LOW PRESSURE ARE FCST TO MOVE ALONG A SW-NE ORIENTED COLD FRONT WHICH SHOULD SLOWLY PROGRESS EWD TOWARD THE COAST WED-THUR AS NRN STREAM ENERGY CROSSES THE GREAT LAKES. THERE ARE SOME DIFFERENCES WITH MODEL QPF BUT THE CONSENSUS POINTS TOWARD THE SRN PA FOR THE HIGHEST PCPN AMTS. USED A MULTI MODEL BLEND WITH PSEUDO BIAS CORRECTION FACTOR TO DERIVE GRIDDED QPF AMTS WHICH CONSERVATIVELY RANGE FROM 0.25 TO 0.75 INCHES ACROSS THE SRN 1/2 OF THE CWA. THE COLUMN WILL BE IN A STATE OF TRANSITION AND COOLING FROM NW TO SE WED-WED NGT AS THE COLD FRONT PUSHES EAST. THIS SHOULD SUPPORT A GENERAL TRANSITION FROM RAIN TO SNOW ACROSS THE CWA. WITH A DECENT AMOUNT OF MSTR AVAILABLE/STRIPE OF ABOVE NORMAL PW LOCATED JUST SOUTH OF PA...THE POTENTIAL EXISTS FOR MODERATE TO HEAVY SNOW OVER THE SRN PORTIONS OF THE AREA. HOWEVER GIVEN THE UNCERTAINTY AT DAY 3-4 RANGE IN THE FRONTAL WAVES AND THERMAL PROFILES IN A STATE OF FLUX GOING FROM WARM TO COLD...CONFIDENCE IN BIG AMOUNTS IS QUESTIONABLE. FOR NOW THE DAY 3+4 NUMBERS RANGE FROM 0-2" NORTH OF I-80...2-4" FROM I80 TO THE PA TURNPIKE/I-81 AND AMOUNTS IN EXCESS OF 4" POSSIBLE ALONG/S OF THE TURNPIKE/I-81. THIS IS SUBJECT TO CHANGE AS ANY SLIGHT SHIFT IN THE QPF AXIS IS PLAUSIBLE AT THIS POINT. THE TAKEAWAY HERE IS THAT WINTER WX WILL LKLY CONTINUE TO IMPACT THE AREA THROUGH MIDWEEK WITH THE GREATEST RISK FOR HEAVY SNOW OVER THE SRN PORTIONS OF THE CWA. WHAT IS HOPEFULLY THE LAST SHOT OF ARCTIC AIR SHOULD ARRIVE BEHIND THE COLD FRONT THURSDAY WITH SINGLE DIGIT LOWS +/- OF FRIDAY MORNING. MAY BE THE COLDEST MORNING UNTIL NEXT WINTER. SOME SNOW SHOWERS ARE POSSIBLE OVER THE WEEKEND WITH A REINFORCING COLD FRONT. TEMPS WILL REMAIN AT OR BELOW AVG THROUGH THE PERIOD. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... CONDITIONS WILL QUICKLY DETERIORATE FROM WEST TO EAST AS MODERATE SNOW BANDS CROSS THROUGH THE CENTRAL AND NORTH CENTRAL MOUNTAINS THROUGH MIDDAY AND EARLY AFTERNOON HOURS. WARMER AIR SURGING IN ON INCREASING SW FLOW WILL BRING A TRANSITION TO A WINTRY MIX/FREEZING RAIN EVENT BY MID TO LATE AFTERNOON INTO THE EARLY EVENING...BEFORE CHANGING TO RAIN /FZRA NORTH/ LATE TONIGHT INTO EARLY WED AS HEAVIER PRECIP GRADUALLY TAPERS OFF. WIDESPREAD SIGNIFICANT RESTRICTIONS TO CIGS/VSBYS WILL ACCOMPANY THIS STORM AT ALL TERMINALS FOR AN EXTENDED PERIOD STARTING LATE THIS MORNING/EARLY THIS AFTERNOON. LLWS WILL ALSO DEVELOP AS 850MB WINDS INCREASE TO AROUND 50 KTS. LATE WED/EARLY THURS AS COLDER AIR WORKS BACK TO THE SOUTH...LOW PRESSURE MOVING NE ALONG THE FRONT WILL LIKELY RESULT IN A NASTY MIXTURE OF PRECIPITATION. POTENTIAL IS THERE FOR HEAVY WET SNOW AND SIGNIFICANT FREEZING RAIN AS WELL. OUTLOOK... WED...SOME IMPROVEMENT TO CONDITIONS BUT SOME REDUCTIONS WILL CONTINUE /ESP SOUTH/ IN RAIN TRANSITIONING BACK TO SNOW LATER IN THE DAY. WED NIGHT...SIG REDUCTIONS IN SNOW DEVELOPING MAINLY ACROSS THE SOUTH. THU...SLOWLY IMPROVING CONDITIONS...LINGERING MVFR NW AND SE. FRI-SAT...MAINLY VFR. && .CTP WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 7 AM EST WEDNESDAY FOR PAZ006-011-012-018-037-041-042. WINTER WEATHER ADVISORY UNTIL 4 AM EST WEDNESDAY FOR PAZ004- 005-010-017-024>026-033>035. WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 4 AM EST WEDNESDAY FOR PAZ019-027-028-036-045-046-049>053-056>059- 063>066. && $$ SYNOPSIS...DEVOIR/LAMBERT NEAR TERM...DEVOIR/LAMBERT SHORT TERM...LAMBERT LONG TERM...LAMBERT/STEINBUGL AVIATION...DEVOIR/RXR

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