Area Forecast Discussion
Issued by NWS State College, PA

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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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