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Area Forecast Discussion
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000
FXUS61 KCTP 220448
AFDCTP

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE STATE COLLEGE PA
1148 PM EST SUN DEC 21 2014

.SYNOPSIS...
A WEAK LOW PRESSURE SYSTEM WILL MOVE NORTHWARD ALONG THE MID
ATLANTIC COAST ON MONDAY. A VIGOROUS STORM SYSTEM WILL PUSH A
COLD FRONT ACROSS THE COMMONWEALTH ON CHRISTMAS EVE BRINGING
WIDESPREAD SHOWERS AND EVEN A CHANCE FOR THUNDERSTORMS. 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 7 AM MONDAY MORNING/...
CLOUDS CONTINUE TO RECEDE NORTHWARD AT 02Z. JUST A COUPLE OF
SPOTS OF LOWER CLOUDS ON THE FOG CHANNEL /11-3.9 MICRON/ OF THE
SAT PICS OVER THE BLUE RIDGE IN VA. IN TIME...THE COMBINATION OF
INCREASING EASTERLY FLOW AROUND THE 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. THIS ACTION IS EXPECTED
TO PRODUCE LOW CLOUDS AGAIN - ESP IN THE CENTRAL MTNS - BY MID
MORNING.

&&

.SHORT TERM /7 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
920 PM UPDATE...
HAVE CONTINUED TO MENTION SOME ZR FOR THE LAURELS/SC MTNS AND UP
INTO THE ALLEGHENIES...AND ALONG THE NRN FRINGE OF THE VERY LIGHT
PRECIP EXPECTED TO MOVE IN FROM THE S LATE MON AFTN/EVENING. SREF
PROB OF ZR ARE VERY HIGH IN THE LAURELS AND ALLEGHENIES FOR THE
EVENING AND MON NIGHT. BUT THE PRECIP IS STILL UNCERTAIN ENOUGH TO
KEEP POPS IN THE HIGH-CHC RANGE...TAPERING OFF RATHER QUICKLY W OF
RTE 219. THEREFORE...STILL NO ADVY TO BE POSTED THIS EARLY/AT THIS
TIME HORIZON DUE TO THE LOW CERTAINTY OF OCCURRENCE OF PRECIP LET
ALONE ZR ACCRETIONS.

PREV..
INCREASING LLVL MOISTURE IS EXPECTED TO BRING SOME SPITTY/SPOTTY
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/RANGE.

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 /04Z MONDAY THROUGH FRIDAY/...
THE PATTERN CONTINUES AS STRATOCU IS TRAPPED UNDER AN INVERSION
THROUGH MAINLY THE NORTH. THE REST OF THE REGION HAS CLEARED. THE
QUESTION OVERNIGHT IS THAT WHETHER ANY OF THE WEAK SOUTHERLY FLOW
ALLOWS FOR STRATOCU TO THICKEN. WITH LIGHT WINDS

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 ESPECIALLY MONDAY.
ANTICIPATE THAT WE/LL SEE REDEVELOPMENT/REINFORCEMENT OF THE
STRATOCU DECK OVER THE SPINE OF THE APPALACHIANS /FROM KJST-KBFD/
OVERNIGHT...THOUGH ANY MID CLOUDS WILL REDUCE FORMATION. EXPECT
MVFR POSSIBLE AT JST AND AOO BETWEEN 09 TO 12Z. THOUGH IFR SHOULD
CONTINUE AT BFD OVERNIGHT INTO TOMORROW. 

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...DANGELO/DEVOIR
SHORT TERM...DANGELO/DEVOIR
LONG TERM...MARTIN
AVIATION...DEVOIR/CERU



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