Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 310233 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 1033 PM EDT MON MAR 30 2015 .SYNOPSIS... A POTENT BUT RELATIVELY FAST MOVING AREA OF LOW PRESSURE WILL MOVE SOUTHEAST FROM THE WESTERN GREAT LAKES TONIGHT AND RIDE ALONG THE MASON-DIXON LINE TUESDAY...BRINGING HIGHLY ELEVATION DEPENDENT SNOW ACCUMULATION OF A FEW TO SEVERAL INCHES ACROSS THE NORTHERN HALF TO TWO THIRDS OF PENNSYLVANIA. MIXED PRECIPITATION OR RAIN WILL FALL ACROSS THE SOUTHERN TIER OF PENNSYLVANIA. A SHARP MODERATION IN TEMPERATURES WILL OCCUR THURSDAY BEFORE A NEW COLD FRONT APPROACHES FOR FRIDAY WITH RAIN SHOWERS...POSSIBLY CHANGING TO A PERIOD OF SNOW AT NIGHT ACROSS MUCH OF CENTRAL AND NORTHERN PENN. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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ISOLATED RAIN/SNOW SHOWERS ARE ALL THAT REMAIN FROM THIS EVENING/S ACTIVITY ACROSS THE NORTH CENTRAL MOUNTAINS. SFC TEMPERATURES ARE MARGINAL...STILL ABOVE FREEZING THROUGHOUT CENTRAL PA...AS PRECIP SHIELD FROM THE APPROACHING CLIPPER SYSTEM IS NOW SHOWING UP OVER NORTHERN OHIO. FORECAST FOR THE OVERNIGHT IS NOT TERRIBLY CHALLENGING...BUT GIVEN THE MARGINAL AMBIENT CONDITIONS...SNOW ACCUMULATION FORECAST FOR TUESDAY REMAINS QUITE UNCERTAIN. CONFIDENCE IS QUITE GOOD IN WIDESPREAD 0.25" TO 0.33" QPF RIBBON FROM SOUTHERN PORTIONS OF THE NORTHWEST MOUNTAINS EXTENDING THROUGH A GOOD PART OF THE NORTHERN HALF OF CENTRAL PA TUESDAY MORNING INTO TUESDAY AFTERNOON. NEAR TERM HI RES AND SHORT RANGE ENSEMBLE SYSTEM DEPICT NEAR ADVISORY CRITERIA SNOWFALL FOR PORTIONS OF THE WEST CENTRAL AND NORTH CENTRAL MOUNTAINS...BUT GIVEN THE MARGINALLY COLD LLVL AIR THINK MOST VALLEY LOCATIONS WILL REMAIN SUB ADVISORY WITH HIGHER ELEVS STANDING THE BEST CHANCE OF SEEING 3"+ OF SNOW ACCUM TUE MORNING INTO EARLY TUESDAY AFTERNOON. LATEST 00Z NAM12...FOR WHAT ITS WORTH...RETURNS QPF BULLSEYE NORTHWARD...TRACKING SFC LOW ALONG OR JUST NORTH OF A KJST TO KAOO PATH...REDUCING SNOW ACCUMS FURTHER ACROSS SOUTHERN CLEARFIELD AND SOUTHERN PORTIONS OF THE CENTRAL MOUNTAINS. ALL OF THE ABOVE TELL ME THAT SLIGHTLY LOWER AMOUNTS AND OVERALL SUBADVISORY ACCUMS WILL BE PREVALENT ON TUESDAY...HOWEVER THIS IS PRELIMINARY WITHOUT A GLIMPSE AT A FULLER SUITE OF 00Z OUTPUT AND THE LATEST EFS DATA WHICH THE MID SHIFT WILL HAVE AT ITS DISPOSAL. WILL MAINTAIN THE EARLIER ISSUED SPS FOR ELEVATION DEPENDENT SNOWFALL FOR NOW. CLOUDS WILL GENERALLY DECREASE ACROSS CENTRAL PA THROUGH 1 AM BEFORE CLOUD SHIELD FROM APPROACHING CLIPPER STREAMS IN AFTER THAT TIME. WINDS WILL TAIL OFF TO LIGHT AND VARIABLE IN MANY LOCATIONS AFTER MIDNIGHT...ALLOWING MIN TEMPS TO REACH THE MID TO UPPER 20S NORTH TO THE LOWER TO MIDDLE 30S SOUTH.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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LATEST TIMING ON THE ARRIVAL OF SNOWFALL SUGGESTS A SLIGHTLY LATER ARRIVAL TUESDAY MORNING...LIKELY STARTING ACROSS THE NORTHWEST...WEST CENTRAL MOUNTAINS AROUND OR SHORTLY PAST DAYBREAK...THEN SPREADING ACROSS THE REMAINDER OF THE REGION DURING THE MID TO LATE MORNING HOURS. MODELS ARE IN GOOD AGREEMENT ON THE TRACK OF A POTENT CLIPPER ALONG THE MASON-DIXON LINE DURING THE DAY TUESDAY. AS PREVIOUSLY MENTIONED...SEVERAL FACTORS COMPICATE THE FORECAST FOR SNOWFALL AMOUNT ACROSS THE REGION TUESDAY. THE FIRST BEING THE EXACT TRACK AND QPF...SECOND IS THE TIMING OF THE HEAVIEST SNOWFALL RATES DURING THE MORNING /A FEW HOURS FASTER MEAN MORE SNOW/...AND THIRD BEING A LARGE DEGREE OF ELEVATION DEPENDENCY. IN ANY CASE...A SEVERAL HOUR PERIOD OF MODERATE TO STG UVVEL ASSOCIATED WITH THE LEFT EXIT REGION OF A 100 KT UPPER JET WILL BRING A PERIOD OF MODERATE TO BRIEFLY HEAVY SNOW TUESDAY MORNING...GRADUALLY TAPERING TO AREAS OF LIGHTER SNOW/SNOW SHOWERS FOR THE MID TO LATE AFTERNOON. LIKELY SNOWFALL WILL VARY FROM 1-3 INCHES IN THE VALLEYS...AND UP TO 4 OR 5 INCHES OF HEAVY WET SNOW ACROSS THE HIGHER TERRAIN NEAR AND TO THE NORTH OF THE RT 322 CORRIDOR. THERE MAY BE LITTLE OR NO SNOW SOUTH OF THE TURNPIKE AND WEST OF INTERSTATE 81...ALONG AND JUST SOUTH OF THE LOW TRACK. AFTER COORDINATION WITH SURROUNDING OFFICES...WE AGAIN ARE LACKING CONFIDENCE FOR ADVISORY ISSUANCE LATE THIS EVENING AND WILL LOOK FOR 00Z NUMERICAL GUIDANCE/LATEST AVAILABLE EFS OUTPOUT FOR FINAL GUIDANCE ON AMOUNTS FOR THIS ELEVATION INFLUENCED BORDERLINE ADVISORY EVENT. MULTI MODEL TEMPS FOR TUESDAY/S MAXES ARE IN THE MID 30S ACROSS THE NRN MTNS...AND UPPER 30S TO MID 40S IN CENTRAL PENN...WITH HIGHS AROUND 50F IN THE SOUTH. UNLESS IT SNOWS FAIRLY HARD...MOST ACCUMS AFTER 15Z WILL LIKELY BE ON GRASSY SURFACES. OVER CENTRAL AREAS WHERE A RAIN-SNOW MIX IS LIKELY FOR A TIME...IT SHOULD BE TOO WARM TO STICK.
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&& .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... SFC LOW WILL EXIT THE NJ/DELMARVA COAST TUESDAY NIGHT WITH HIGH PRESSURE ARRIVING FROM THE GREAT LAKES. DRY WEATHER WILL PERSIST THROUGH MIDWEEK BEFORE THE PATTERN TURNS INCREASINGLY UNSETTLED FROM THURSDAY INTO EASTER WEEKEND. THE 12Z MODEL AND ENSEMBLE DATA SEEMS TO BE COMING AROUND TO THE IDEA THAT ONE OR TWO FRONTAL WAVES WILL BRING PCPN TO THE AREA FROM THURSDAY INTO SATURDAY. THERE IS STILL SOME SPREAD IN BOTH THE TRACK AND STRENGTH OF THE TRAILING FRONTAL WAVES WITH THE LAST TWO RUNS OF THE EC COMING IN MUCH STRONGER THAN THE GFS. THE CANADIAN IS IN THE MIDDLE IN TERMS OF POSITION BUT LEANS TOWARD THE STRONGER EC. AT ANY RATE THE DETAILS ARE STILL UNCLEAR BUT A MEAN BLEND/CONSENSUS SOLUTION INCORPORATING WPC GUIDANCE SUPPORTS INCREASING POPS INTO THE LKLY RANGE FOR AT LEAST TWO 12-HOUR PERIODS. A SHORTWAVE TROUGH ROTATING THROUGH THE MID ATLC AND NORTHEAST STATES WILL BRING A REINFORCING SHOT OF COOL AIR ON SATURDAY...PRECEDED BY ABOVE NORMAL TEMPS AHEAD OF THE COLD FRONT. THE COOL DOWN SHOULD BE BRIEF WITH MODERATING TEMPS INTO EARLY NEXT WEEK. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... UPPER TROF SLIDING EASTWARD THIS EVENING OVER SOUTHERN NEW YORK STATE ALONG WITH STEEP LOW-LEVEL LAPSE RATES IS MAINTAINING SCATTERED SNOW AND RAIN SHOWER ACTIVITY ACROSS THE NORTHERN MOUNTAINS THIS MID EVENING...WITH INTERMITTENT CIG/VSBY REDUCTIONS IN THE MOST INTENSE CELLS. EXPECT THUS ACTIVITY TO DECREASE BY LATE EVENING (03Z-04Z) AS UPPER TROF AXIS SLIDES EAST AND LLVLS STABLIZE. CONDITIONS SHOULD RETURN TO VFR AREAWIDE FROM LATE EVENING HEADING TOWARD SUNRISE...WITH WINDS DIMINISHING BELOW 10 MPH. A FAST MOVING ALBERTA CLIPPER WILL BRING ANOTHER EARLY SPRING WINTRY WEATHER EVENT TO MUCH OF CENTRAL AND NORTHERN PENN. REDUCTIONS WILL BEGIN AROUND OR SHORTLY BEFORE DAYBREAK TUESDAY ACROSS THE WESTERN MTNS...THEN SPREAD ACROSS THE REMAINDER OF THE REGION DURING THE MID TO LATE MORNING HOURS. A SHIELD OF STEADY LIGHT TO MDT SNOW ACROSS THE NORTHERN THIRD OF PENN WILL DROP CONDITIONS TO IFR/LIFR FROM BFD TO POINTS EAST TWD KIPT BY MID MORNING TUE. IFR IN MIXED PRECIP OR SNOW APPEARS LIKELY FOR THE CENTRAL THIRD OF THE STATE TUESDAY MORNING/EARLY AFTERNOON...WHILE A FEW PERIODS OF LIGHTER RAIN/SNOW SHOWERS WILL OCCUR ACROSS THE SOUTHERN TIER COUNTIES OF PENNSYLVANIA WITH GENERALLY MVFR CIGS/VSBYS. SOME LIGHTER AND MORE BRIEF RAIN AND SNOW SHOWERS REMAIN FROM LATE TUESDAY AFTERNOON INTO EARLY WEDNESDAY...IN THE WAKE OF THE EXITING LOW PRESSURE AREA. OUTLOOK... WED-THU MORNING...MAINLY VFR...AS HIGH PRESSURE BUILDS ACROSS THE AREA. THU PM-FRI...LOWERING CONDITIONS TO MVFR WITH SCATTERED RAIN SHOWERS...AS A COLD FRONT MOVES EASTWARD. GUSTY SW WIND DEVELOPING. SAT...LOW PROB FOR RAIN SHOWERS /MIXED WITH SNOW SHOWERS NORTH/. REDUCTIONS POSS MAINLY NORTHERN MTNS. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...LA CORTE/LAMBERT NEAR TERM...DEVOIR/LAMBERT SHORT TERM...DEVOIR/LAMBERT LONG TERM...STEINBUGL AVIATION...RXR

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