Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 212059
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
359 PM EST SUN DEC 21 2014

.SYNOPSIS...
HIGH PRESSURE OVER QUEBEC WILL SHIFT EASTWARD...DELIVERING AN
INCREASINGLY MOIST EASTERLY FLOW INTO THE REGION AS A WEAK LOW
PRESSURE SYSTEM TRACKS ALONG THE MID ATLANTIC COAST. PATCHY LIGHT
PRECIPITATION WILL DEVELOP ON MONDAY...PRIMARILY RAIN...BUT A FEW
SPOTS COULD SEE SOME PATCHY FREEZING RAIN IF IT DEVELOPS EASTERLY
ENOUGH IN THE DAY. MEANWHILE...A VIGOROUS STORM SYSTEM WILL SWEEP
ACROSS THE COMMONWEALTH ON CHRISTMAS EVE DAY BRINGING WIDESPREAD
SHOWERS AND A CHANCE FOR THUNDERSTORMS ON CHRISTMAS EVE. WINDY
AND COLDER CONDITIONS WILL FOLLOW WITH SCATTERED SNOW SHOWERS
ACROSS THE WEST AND NORTH FOR CHRISTMAS DAY. DRY AND SEASONABLE
CONDITIONS ARE EXPECTED FOR FRIDAY AND SATURDAY BEFORE MORE
UNSETTLED WEATHER ARRIVES FOR THE SECOND HALF OF THE WEEKEND.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
THE THIN STRATUS CONTINUES TO THIN FURTHER ACROSS THE CENTRAL
MOUNTAINS...WITH VISIBLE IMAGERY SUGGESTING IT MAY GIVE WAY TO AN
HOUR OR TWO OF SUNSHINE IN SOME AREAS BEFORE SUNSET. THE FAR NORTH
MAY SEE SOME BRIGHTENING BUT BKN-OVC WILL REMAIN THERE LATE THIS
AFTERNOON AND EVENING. RETURN FLOW AROUND QUEBEC SFC HIGH SHOULD
CONTINUE THIS TREND THIS EVENING...AS RETURN FLOW SOURCE AREAS
SOUTH OF THE MASON DIXON LINE HAVE ALSO CLEARED FOR THE MEANTIME.

HOWEVER...IN TIME THE COMBINATION OF INCREASING EAST FLOW AROUND
RETREATING HIGH PRESSURE OVER NEW ENGLAND AND WEAK LOW PRESSURE
DRIFTING NORTHWARD FROM THE CAROLINAS ALONG THE MID ATLANTIC COAST
WILL SHUNT WESTERN ATLANTIC LOW LEVEL MOISTURE ONSHORE LATER
TONIGHT. AS PREVIOUSLY MENTIONED...INCREASING MOISTURE...COMBINED
WITH LG SCALE FORCING AHEAD OF SHORTWAVE LIFTING OUT THE OHIO
VALLEY...IS EXPECTED TO PRODUCE SOME PRECIPITATION...BUT CONSENSUS
STILL POINTS TO LATER ON MONDAY.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
AS MENTIONED IN THE NEAR TERM SECTION...INCREASING LLVL MOISTURE
IS EXPECTED TO BRING SOME SPITTY NUISANCE TYPE PRECIPITATION
ACROSS SOUTHERN AND SOUTHEASTERN AREAS ON MONDAY...MAINLY
AFTERNOON. NAM12 REMAINS AGGRESSIVE IN PUSHING MOISTURE NORTH OF
THE MASON DIXON LINE AFTER 12Z...AN OUTLIER...WHICH WOULD
INTRODUCE PRECIP TYPE ISSUES GIVEN RESIDUAL MARGINAL COLD AIR
MONDAY MORNING. CONTINUE TO DOWNPLAY THAT MODEL AND SOLUTION...AND
FAVOR A CONSENSUS LATER ARRIVAL OF LIGHT PRECIP...WHICH WOULD
STILL PRODUCE SOME PATCHY MIXED PRECIP AT THE ONSET. CONFIDENCE
STILL TOO LOW ON THIS FOR ANY ADVISORY CONSIDERATION AT THIS TIME.

DEPENDING UPON TIMING OF ARRIVAL...AREAS WHICH MAY BE MOST
SUSCEPTIBLE TO BRIEF -FZRA MON AFTERNOON WOULD BE OVER PARTS OF
THE CENTRAL AND SOUTH CENTRAL MOUNTAINS. STILL MONITORING THIS LOW
PROBABILITY EVENT AT THIS TIME...AND WILL MENTION LOW CHANCES IN
GRIDS/TEXT PRODUCTS.

&&

.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
FOR MONDAY NIGHT...DID NOT CHANGE A LOT. NAM MODEL LOOKS A
LITTLE WET...SO DID NOT UP POPS A LOT. WENT FOR A MIX OF
RAIN AND FREEZING RAIN...PCPN AMTS NOT MUCH MORE THAN .O1.
MORE LIKE A DRIZZLE. STILL THIRD PERIOD...TOO EARLY FOR AN
ADVISORY. THE MOIST SERLY FLOW OFF THE ATLANTIC AND ASSOC
OROGRAPHIC FORCING OF SHALLOW MOISTURE LYR WILL LINGER INTO
TUE MORNING...BUT SHOULD EDGE TO THE EAST DURING THE DAY. AFTER
HAVING LOWS IN THE 31-32 DEGREE RANGE...TEMPS SHOULD EDGE UP SOME
DURING THE DAY ON TUE.

DID NOT CHANGE A LOT FOR TUE...SOME RAIN DURING THE DAY
INTO TUE NIGHT...BUT NOT ALL THE TIME. LOW RATHER FAR TO
THE WEST FOR STRONG FLOW TO MOVE COLDER AIR OUT.

THE MOST SIGNIFICANT FORECAST ISSUE IN THE LONG TERM REMAINS THE
EVOLUTION OF DEEP TROUGH AND ASSOC SFC LOW TO OUR WEST 24-25
DECEMBER. STRONG SOUTHERLY FLOW AHEAD OF THIS SYSTEM WILL BRING
SOME OF THE WARMER AIR INTO THE REGION ON WEDNESDAY...AS MANY
LOW-LEVEL TEMPERATURE AND MOISTURE FIELDS RISE WELL ABOVE THEIR
SEASONAL VALUES. THIS IMPLIES WARMER TEMPS ON WEDNESDAY...AS THE
SHALLOW COLD AIR SCOURS OUT EAST OF THE MOUNTAINS.

NEW MODELS SLOW FRONT SOME...THUS DID UP POPS WED NIGHT AND
GO ALL RAIN.

COLDER AIR WORKS IN FOR CHRISTMAS...BUT SNOW SHOWERS WILL
BE MAINLY CONFINED TO THE WESTERN MOUNTAINS...AND NOT REAL
COLD.

MILDER AIR WORKS IN FOR FRIDAY ON SW FLOW.

COLDER AIR AGAIN FOR LATER IN THE WEEKEND...AS ANOTHER
COLD FRONT MOVES ACROSS THE AREA.

&&

.AVIATION /21Z SUNDAY THROUGH FRIDAY/...
STRATOCU TRAPPED UNDER INVERSION CENTRAL AND NORTH...WHILE AN
AREA OF PARTIAL CLEARING EXTENDS FROM SC MTNS TO LOWER SUSQ
PROVIDING VFR CONDITIONS. MVFR CIGS WILL BE PREVALENT CENTRAL
AND NORTH...WHILE PARTIAL CLEARING FLIRTS WITH THE SOUTHERN TIER.

COMBINATION OF RETREATING HIGH PRESSURE OVER NEW ENGLAND AND WEAK
LOW LIFTING UP THE EAST COAST WILL BRING A GRADUALLY INCREASING
MOIST SERLY FLOW INTO CENTRAL PA LATE TONIGHT AND ESP MONDAY.
ANTICIPATE THAT WE/LL SEE REDEVELOPMENT/REINFORCEMENT OF THE
STRATOCU DECK OVER THE SPINE OF THE APPALACHIANS /FROM KJST-KBFD/
TONIGHT...POSS SPREADING INTO CENTRAL MTNS...WITH MOST POINTS EAST
REMAINING VFR.

THE INCREASING MOISTURE...COMBINED WITH LG SCALE FORCING AHEAD OF
SHORTWAVE LIFTING OUT THE OHIO VALLEY...COULD SPREAD A BIT OF
LIGHT PRECIPITATION INTO SOUTHERN PA MONDAY PM.

OUTLOOK...

MON...CIG REDUCTIONS WEST. RESTRICTIONS DEVELOPING EAST. LIGHT
RAIN POSS SOUTH...FZRA POSS WESTERN HIGHER TERRAIN. BECOMING
BREEZY.

TUE...LOW CIGS WITH DRIZZLE/LIGHT RAIN LIKELY. BREEZY.

WED...PERIODS OF RAIN ALONG WITH WIDESPREAD REDUCTIONS. WINDY
WITH LLWS.

THU...WINDY AND COLDER WITH SCT MVFR CIGS AND -SHSN. LLWS.

FRI...FAIR AND MOSTLY VFR.

&&

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

&&

$$
SYNOPSIS...DEVOIR
NEAR TERM...DEVOIR
SHORT TERM...DEVOIR
LONG TERM...MARTIN
AVIATION...DEVOIR/RXR



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