Area Forecast Discussion
Issued by NWS State College, PA

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000 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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