-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KCTP 110602
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
202 AM EDT TUE MAR 11 2014

.SYNOPSIS...
A CLIPPER LOW WILL TRACK RAPIDLY THROUGH UPSTATE NEW YORK AND
NORTHERN NEW ENGLAND TONIGHT INTO TUESDAY. A LATE WINTER STORM
SYSTEM WILL IMPACT THE AREA ON WEDNESDAY...FOLLOWED BY COLD AND
BLUSTERY CONDITIONS FOR END OF THE WEEK.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
CLIPPER PASSING ACROSS CENTRAL ONTARIO THIS EVENING. VIGOROUS H5
SHEAR AXIS ROCKETING ACROSS UPSTATE NEW YORK TO CENTRAL NEW
ENGLAND BY 06Z... REFLECTED AT 850 MB BY A 50+KT LLJ MOVING OVER
PA/NY STATE THROUGH LATE TONIGHT. OTHER THAN A STRAY SPRINKLE OR
FLURRY OVER THE NORTHERN MTNS...IT WILL REMAIN DRY AND RELATIVELY
MILD TONIGHT. A STRATOCU DECK IS FILTERING IN FROM THE NW AS PER
LATEST GOES IMAGERY AND WILL ARRIVE AFTER MIDNIGHT. OVERNIGHT LOWS
MAINLY IN THE 30S WILL BE ABOVE NORMAL BY 10 DEGREES OR SO IN MOST
AREAS...WITH A BIT OF A BREEZE.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
TUESDAY LOOKS TO BE ANOTHER PLEASANT DAY WITH MILD WEATHER
CONTINUING. HIGHS SHOULD BE COMPARABLE TO TODAY...SLIGHTLY ABOVE
AVERAGE. EARLY MORNING STRATOCU WILL DISSIPATE QUICKLY...LEAVING
BEHIND PLENTY OF SUN IN THE MORNING...WHICH WILL FADE BEHIND
INCREASING MID/HIGH CLOUDS DURING THE AFTERNOON.

FRONTAL BOUNDARY NORTH OF THE AREA WILL BEGIN TO SLOWLY SLIP
SOUTHWARD TUE NIGHT AHEAD OF APPROACHING STORM SYSTEM FROM THE
CENTRAL PLAINS/MISSOURI VALLEY. AS FLOW AHEAD OF THE LOW TURNS
MORE SOUTHERLY...IT WILL CONTINUE TO FEED MILDER AIR INTO CENTRAL
PA. BUT IT WILL ALSO INTERACT WITH THIS FRONTAL BOUNDARY TO
INITIATE LIGHT PRECIPITATION BY LATE EVE TUE. INITIALLY...LIGHT
RAIN SHOULD BE CONFINED MAINLY TO NW PORTIONS OF CWA...WITH A
GRADUAL CHANGEOVER TO LIGHT SNOW OVERNIGHT AS COLDER AIR BEGINS TO
UNDERCUT THE WAA. LIGHT ACCUMS OF SNOW WILL BE POSS MAINLY IN THE
NW MTNS THROUGH 12Z WED. THE MAIN IMPACTS FROM THIS STORM SYSTEM
WILL BE ON WED.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
AN INTERESTING PATTERN SETTING UP FOR THE MID-WEEK PERIOD...WITH AN
EARLY MARCH WINTER STORM SYSTEM SET TO IMPACT THE REGION...REMINDING
FOLKS SPRING IS NOT HERE QUITE YET.

SPLIT-STREAM H5 ENERGY WILL PROCEED DOWNSTREAM FROM THE CENTRAL
PLAINS/MID-LWR MS VLY EARLY WEDNESDAY...BEFORE INTERACTING WITH
STRONG HEIGHT FALLS/SURGE OF ARCTIC AIR POURING SWD FROM THE UPPER
MIDWEST. THE RESULT APPEARS TO BE AN INCREASINGLY ROBUST...POSSIBLY
PHASED SYSTEM WITH AN INITIALLY FLAT WAVE OF SFC LOW PRES TRACKING
EWD ALONG THE OH RVR BEFORE RAPIDLY INTENSIFYING 15-20MB AS IT
CROSSES SRN PA/NRN MD/VA AND ACHIEVING COASTAL NOR`EASTER STATUS
AS IT LIFTS NEWD ALONG THE NJ/SRN NEW ENGLAND COAST. THE STORM SYS
SHOULD EXIT INTO SERN CANADA ON THURS.

OVERALL...THE MODEL SPREAD REMAINS REASONABLY LOW REGARDING THE
LARGE SCALE FEATURES OF THIS EVOLVING STORM SYS. A WIDESPREAD AND
RATHER HIGH IMPACT LATE-WINTER/EARLY MARCH PCPN EVENT WILL UNFOLD
ACRS THE AREA...INCLUDING POTENTIAL FOR SIGNIFICANT WINTER
WX/HEAVY SNOW ACCUMS IN NORTH-CNTRL PA. THE DEVIL..OF COURSE...WILL
BE IN THE DETAILS...SPECIFICALLY REGARDING THE PLACEMENT OF THE
RAIN/SNOW LINE WHICH AS BEEN WAFFLING N-S AND HAS ESSENTIALLY
TRENDED A BIT NWD BASED ON A CONSENSUS OF THE LATEST 10/12Z
OPERATIONAL MODEL AND ENSEMBLE GUIDANCE.

THE 12Z CMC AND 12Z NAM ARE FASTER AND RELATIVELY WEAKER COMPARED TO
THE GLOBAL MODEL CONSENSUS WITH RESPECT TO THE EVOLVING SFC LOW. THE
12Z ECMWF/12Z UKMET AND 12Z GFS ARE A BIT SLOWER. THE 12Z UKMET
AND ESP THE 12Z GFS NOT ONLY TRENDED SLOWER...BUT ARE ALSO NOTABLY
STRONGER AT THE SFC AND ALOFT. THE 10/15Z SREF MEAN AND 10/12Z
GEFS ARE BOTH SLOWER THAN THE CMC BUT COMPARABLE IN DEPTH TO BOTH
THE NAM/CMC. THE 12Z GFS AND 12Z ECMWF SHOW REASONABLY GOOD
AGREEMENT...WITH THE 12Z GFS A LITTLE STRONGER BUT SLIGHTLY NORTH
OF THE 12Z ECMWF SFC LOW TRACK...WHICH IS REMARKABLY CONSISTENT
WITH ITS (THE EC) PREVIOUS RUN.

AS IT APPROACHES FROM THE OH VLY LATE TUE NGT...THE PRECIP SHIELD
INITIALLY WILL BE DRIVEN BY ISENTROPIC LIFT/WARM ADVECTION PATTERN
WHILE THE WAVE REMAINS RELATIVELY FLAT/WEAK. THIS OVERRUNNING PCPN
WILL THEN TRANSITION TO A MORE ROBUST...HEALTHY DEFORMATION
ZONE/DYNAMIC COOLING PRECIP SHIELD AND EXPAND INTO THE NRN MID-ATLC
AND NORTHEAST STATES FROM WED AFTN INTO WED NGT. THE MAIN CHALLENGE
WITH THIS SYSTEM WILL BE THE PLACEMENT AND EVOLUTION OF THE
RAIN/SNOW LINE OR 0C 850MB ISOTHERM...WHICH SHOULD START OUT AT A
W-E POSITION SOMEWHERE BTWN I80 AND THE PA/NY BORDER...THEN SHIFT
SEWD THRU 00Z THU AS MUCH COLDER AIR PLUNGES SWD ON THE BACKSIDE
OF THE DEEPENING LOW PRES SYSTEM. THE LLVL THERMAL 850MB GRADIENT
IS QUITE IMPRESSIVE RANGING FROM -5C IN THE FAR NW TO AROUND +10C
IN THE EXTREME SE. THE WARMER AIR ALOFT...ESPECIALLY ON THE SRN
PERIPHERY OF THE PCPN SHIELD..SHOULD RESULT IN A BAND OF MULTIPLE
PRECIPITATION TYPES IN THE TRANSITION ZONE BUT FOR NOW WILL ONLY
MENTION RAIN->SNOW AS THESE SHOULD BE THE PRIMARY OR DOMINANT
TYPES. THE SNOWFALL FORECAST IS RATHER TRICKY AT THIS POINT WITH
N-S SHIFTS IN THE RAIN/SNOW LINE MAKING ALL THE DIFFERENCE IN
HEAVY SNOW VS. MIXED PCPN VS. MAINLY RAIN. WILL CONTINUE TO PAINT
THE HIGHEST PROBABILITIES OF ALL SNOWFALL AND SIGNIFICANT ACCUMS
OVER THE FAR NRN TIER ZONES. WILL GO FOR LOWER AMTS ALONG THE
I-99/I-80 CORRIDORS FROM THE LAUREL HIGHLANDS THROUGH THE CNTRL
MTNS AND INTO THE LYCOMING/MID-SUSQ VLY...WITH LITTLE TO NO ACCUM
OVER THE FAR SE/LWR SUSQ VLY WHERE WARM AIR WILL BE MOST
PRONOUNCED. THIS OF COURSE IS SUBJECT TO CHANGE WITH THE GENERAL
UNDERSTANDING THAT ADDITIONAL REFINEMENTS ARE LIKELY. FWIW...THE
NAM AND NAM-WEIGHTED SREF MEAN WERE THE MOST AGGRESSIVE WITH THE
WARMING ALOFT AND THUS POTENTIAL FOR FREEZING RAIN..WHILE OTHER
GLOBAL MODELS DEPICTED SPOTTY AREAS WITH LIGHTER AMOUNTS.

WHILE OVERALL CONFIDENCE IS AVERAGE...DECIDED TO HOLD OFF ON ISSUING
A WINTER STORM WATCH FOR THE NRN TIER ZONES. UNLESS THERE ARE
SIGNIFICANT DEVIATIONS IN THE MODELS FROM THEIR CURRENT
RUNS...ANTICIPATE SOME HEADLINES BEING ISSUED FOR THE NRN 1 OR 2
STRIPES OF COUNTIES IN THE COMING SHIFTS. FOR NOW...WE BROKE-OUT THE
HWO TO BETTER DEFINE THE WINTER WX THREATS AND POTENTIAL SNOW
ACCUMS. SPAGHETTI PLOTS OF MODEL 850MB LOW TRACKS SUGGEST
SIGNIFICANT SNOWS...SHOULD THEY VERIFY...WOULD BE CONFINED TO
EXTREME NW/N-CNTRL PA WITH A MESSY TRANSITION TO THE SOUTH AND
MAINLY RAIN OVER THE HRB/LNS AREA..PERHAPS ENDING AS A PERIOD OF
WET SNOW.

AFTER THE STORM...QUITE COLD AIR...AROUND -20C AT 850MB...GETS
DRIVEN INTO THE REGION ON A STRONG GUSTY NW WIND LATER WED NIGHT
INTO THU...WITH BY FAR THE COLDEST DAY OF THE WEEK IN STORE
THURSDAY. WIND CHILLS SHOULD REACH NEAR ADVISORY CRITERIA OVER THE
NRN MTNS AND LAUREL HIGHLANDS...RANGE FROM 0 TO -10F OVER THE
CENTRAL RIDGE/VALLEY REGION AND DIP TO AROUND ZERO IN THE LWR
SUSQ. VLY.

THE WELL-BELOW NORMAL COLD WILL BE SHORT-LIVED THOUGH...AS TEMPS
REBOUND DECENTLY FRI INTO SAT...BOUNCING BACK TO NEAR SEASONAL
NORMALS. HOWEVER THIS WINTER`S DEFINING FEATURE...THE PERSISTENT
WEST COAST RIDGE...IS AGAIN EXPECTED TO RE-ESTABLISH ITSELF
HEADING INTO NEXT WEEK. THIS WILL ALLOW FOR COOLER AIR TO FILTER
BACK INTO THE REGION IN PERSISTENT NW FLOW OVER PA...KEEPING TEMPS
NEAR OR SLIGHTLY BELOW NORMAL AND PREVENTING ANY KIND OF
SIGNIFICANT WARM UP.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
MAINLY CLEAR OUT...WITH VERY STRONG WIND FIELDS. ADDED LLWS TO
A FEW SITES. OFF DUTY STAFF IN AOO HAVE WIND GUST TO AROUND
40 MPH.

MORE ADVERSE CONDITIONS ON WED...CONCERN WILL BE STRONG WIND
FIELDS...LLWS...RAIN ACROSS MUCH OF THE AREA...PERHAPS SOME
SNOW ACROSS THE NW...AND SOME RISK OF STRONG TO EVEN SEVERE
THUNDERSTORMS NEAR THE MD BORDER. THIS WILL BE FOLLOWED BY
MORE STRONG WINDS LATE WED INTO EARLY THU...AS VERY COLD AND
DRY AIR ADVECTED SOUTHWARD INTO THE AREA.

EARLIER DISCUSSION BELOW.

SATELLITE LOOP SHOWS MAINLY CLEAR SKIES ACROSS CENTRAL PA AS OF 03Z.
THE MAIN AVIATION CONCERN LATE THIS EVENING WILL BE THE THREAT OF
LLWS. A CORE OF STRONG WINDS ALOFT WILL PUSH OVER CENTRAL PA THIS
EVENING IN ASSOCIATION WITH APPROACH OF DYING COLD FRONT. MDL
SOUNDINGS INDICATE LLWS CRITERIA WILL LIKELY BE MET OVER MUCH OF
CENTRAL PA BTWN 03Z-07Z WITH LESS OF A CHANCE ACROSS THE
AIRFIELDS OF SOUTHEAST PA.

CORE OF STRONG WINDS ALOFT SHOULD WEAKEN AS DYING FRONT STALLS
OUT ACROSS SOUTHERN PA...RESULTING IN A DIMINISHING THREAT OF LLWS
AFTER ABOUT 07Z. THERE IS SOME CONCERN THAT PLUME OF LOW LVL MOISTURE
ALONG FRONT...COMBINED WITH OROGRAPHIC LIFT...COULD PRODUCE A
PERIOD OF MVFR CIGS AT KJST LATE TONIGHT AND TUE AM.

ANY LOWER CIGS ARND KJST SHOULD LIFT TO VFR BY MIDDAY. FOR TUE
AFTN...GENERALLY VFR CONDS APPEAR LIKELY...WITH THE HIGHEST
CONFIDENCE OF VFR CONDS ACROSS THE EASTERN HALF OF THE STATE...DUE
TO DRYING...DOWNSLOPING WEST WIND.

OUTLOOK...
WED...MVFR-IFR RESTRICTIONS LKLY IN RAIN AND/OR SNOW. WINDY LATE.
THU...STRONG/GUSTY NNW WINDS POSSIBLE.
FRI-SAT...NO SIG WX EXPECTED.

&&

.HYDROLOGY...
WITH WARMER TEMPERATURES FOLLOWED BY MIDWEEK RAINFALL EXPECT MODERATE
RISES ON RIVERS AND STREAMS MAINLY FOR THE SOUTHERN HALF OF THE CWA.
STILL ENOUGH ICE IN SPOTS TO BRING ICE JAMS...THOUGH SIGNIFICANT
DECAY HAS OCCURRED AT MANY LOCATIONS. ANY ICE JAMS WILL BE
ISOLATED IN NATURE. ALL PERSONS SHOULD MONITOR WATER LEVELS
CLOSELY FOR THE REST OF THE WEEK.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$
SYNOPSIS...RXR
NEAR TERM...DEVOIR/RXR
SHORT TERM...RXR
LONG TERM...STEINBUGL
AVIATION...FITZGERALD/MARTIN
HYDROLOGY...CR