Area Forecast Discussion
Issued by NWS State College, PA

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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/...
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.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/...
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.

&&

.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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