000 FXUS61 KCTP 100802 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 302 AM EST FRI FEB 10 2012 .SYNOPSIS... HIGH PRESSURE CENTERED OVER THE OHIO VALLEY WILL SLIDE EAST TO THE CAROLINA COAST ON FRIDAY. A WEAK WAVE OF LOW PRESSURE PASSING TO THE SOUTH WILL MAKE LIGHT SNOW ACROSS THE SOUTHEAST ON FRIDAY NIGHT. AN AMPLIFYING UPPER LEVEL TROUGH OVER THE EASTERN CONTINENT WILL SEND A STRONG COLD FRONT ACROSS THE STATE SATURDAY MORNING. BEHIND THE FRONT...MODIFIED ARCTIC AIR WILL POUR INTO THE REGION FOR THE WEEKEND. TEMPERATURES WILL MODERATE BY MID WEEK. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... MOISTURE TRAPPED UNDER STRONG SUBSIDENCE INVERSION OVER OHIO HAS LED TO AN EXPANDING STRATUS DECK WHICH HAS PROPOGATED INTO SOUTHWEST PA OVER THE LAST HOUR. MEANWHILE...BKN HIGH CLOUDS ASSOCIATED WITH AN EJECTING SHORTWAVE COVER MUCH OF CENTRAL AND EASTERN PA AT THIS HOUR. UPDATED SKY GRIDS AND ZONES FOR THIS... AS HIGH PRESSURE BUILDS EASTWARD ALONG THE MASON DIXON LINE OVERNIGHT. MOISTURE LAYER IS SHALLOW AS PREVIOUS FORECASTER NOTED...SO EXPECTED AREAS EAST OF THE ALLEGHENY PLATEAU TO CONTINUE TO SEE JUST SCT TO OCNLY BKN STRATUS AS THE DECK MOVES EASTWARD OVER THE NEXT SEVERAL HOURS. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... VERY COMPLICATED PATTERN UNFOLDS ON FRIDAY AND INTO SATURDAY. TWO MAJOR PLAYERS IN THE FORECAST- THE STRONG SURGE OF VERY COLD AIR /COMPARED TO WHAT THIS WINTER HAS BEEN LIKE SO FAR/...AND A WEAK TROUGH MOVING THROUGH THE SRN/CENTRAL APPALACHIANS FRIDAY NIGHT. EARLY SUNSHINE WILL FADE BEHIND LOWERING/THICKENING CLOUDS FRIDAY...AS SHORTWAVE OVR THE S PLAINS LIFTS NE TOWARD PA. ALL MDL OUTPUT SUGGESTS AN AFTN ONSET OF PRECIP ACROSS SOUTHERN PA. ALTHOUGH THIS WILL BE PRIMARILY A SNOW EVENT...MDL BLYR TEMPS ONLY MARGINALLY COLD ENOUGH TO SUPPORT SNOW ACROSS THE LOWER SUSQ LATE FRIDAY...SO HAVE MENTIONED EITHER SNOW OR RAIN DOWN THERE LATE FRI AFTN AND EVENING. ARRIVAL OF HEAVIER PRECIP RTS AFTER SUNSET SHOULD TURN ANY RAIN TO ALL SNOW ACROSS THE SE ZONES FRI EVENING. THE STEADY EASTWARD MOTION TO THE ISENTROPIC LIFT WILL CREATE A 6 TO 9 HR PERIOD OF LIGHT TO MDT SNOW ACROSS ROUGHLY THE SOUTHERN 2/3RDS OF PA. SNOW MICRO PHYSICS TELL OF A LOWER SLR THAN MIGHT BE EXPECTED WITH -4 TO -6C 8H TEMPS...AS THE BEST LIFT IS HIGH IN THE CLOUDS...GENERALLY ABOVE THE GOOD DENDRITIC SNOW GROWTH ZONE. QPF BLEND OF 18Z OPER RUNS AND GEFS SUPPORT SNOW TOTALS FRI AFTN/NIGHT OF ARND 1 INCH SOUTH OF I-80...WITH PERHAPS 2 OVR THE LAUREL HIGHLANDS. LESS THAN AN INCH EXPECTED FOR MOST SPOTS NORTH OF I-80. THE SECOND FEATURE WILL BE MORE DRAMATIC WITH THE STRONG COLD ADVECTION MOVING DOWN THRU THE LOWER LAKES LATE FRI NIGHT. AHEAD OF THE FRONT...SOME LIGHT SNOW/SHOWERS MAY BREAK OUT BY LATE EVENING OVR THE N MTNS IN THE VERY LIGHT/BROAD MID-LEVEL ASCENT. UPSLOPE FLOW FROM WSW WINDS SHOULD ALSO AID IN CLOUD DEVELOPMENT AND SEEDING FROM ABOVE. THE MAIN STORY WILL BE THE SQUALLS THAT WILL BE POSSIBLE/LIKELY WITH AND RIGHT AROUND THE TIME OF FROPA. STEEP LLVL LAPSE RATES IN THE SUNRISE HOURS WILL SET THINGS UP FOR SQUALLS TO MOVE DOWN FROM THE NW BEGINNING AFTER 06Z - MORE-LIKELY AFTER 09Z...AND PUSH THRU THE NWRN HALF OF THE AREA BY 15Z. ANY SQUALLS WILL MOST LIKELY CREATE VERY LOW/NEAR ZERO VSBYS AND BRIEF BUT INTENSE SNOW BURSTS. HOWEVER...THE ACCUMULATIONS WILL BE LESS THAN 2 INCHES IN MOST PLACES DUE TO THE FAST MOVEMENT OF THE SQUALLS. OROGRAPHIC ENHANCEMENT COULD PRODUCE 1-3 INCHES OVR THE LAUREL HIGHLANDS SAT. EAST OF THE ALLEGHENY PLATEAU...DOWNSLOPING FLOW WILL LIKELY LIMIT ANY ACCUMS TO LESS THAN AN INCH. LIGHT WINDS EARLY IN THE DAY WILL BECOME STRONGER AND GUSTY BY AFTN...AS THE COLD FRONT SWEEPS IN AND GRADIENT TIGHTENS WEST OF DEVELOPING COASTAL LOW. THE GUSTY WINDS AND FALLING TEMPS WILL LIKELY CREATE WIND CHILLS IN THE SINGLE DIGITS BY LATE IN THE DAY ACROSS THE W MTNS AND TEENS ELSEWHERE. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... SHARP 5H TROF AXIS USHERING ARCTIC AIR INTO THE COMMONWEALTH CROSSES CENTRAL PA EARLY SATURDAY EVENING. AS DYNAMIC FORCING EXITS TO THE EAST...CHANNELED NORTHWEST FLOW WILL LIKELY PRODUCE UPSLOPE SNOW OVER THE LAUREL HIGHLANDS ALONG WITH LAKE EFFECT BANDING ACROSS THE NORTHWEST AND NORTHERN MOUNTAINS. LIGHT TO LOCALLY MODERATE ACCUMULATIONS ARE POSSIBLE IN THE LAUREL HIGHLANDS AND LAKE EFFECT SNOWBELT REGIONS. 1040 SFC HIGH CENTERED OVER THE HIGH PLAINS SATURDAY EVENING WILL TRACK SEWD TO THE LOWER MISSISSIPPI RIVER VALLEY BY SUNDAY EVENING AND THEN NORTHEASTWARD TO THE WV/MD PANHANDLE REGION BY LATE MONDAY. AS A RESULT...COLDEST AIR MOVES OUT OF THE AREA SUNDAY NIGHT AND MONDAY...WITH MODERATION IN STORE EACH DAY THROUGH THE MIDDLE OF NEXT WEEK. WIND CHILLS AS COLD AS -15F ARE POSSIBLE ON SUNDAY. CHC OF LIGHT SNOW RETURNS LATE MONDAY NIGHT INTO TUESDAY IN THE RETURN WSW FLOW ALOFT OVERRUNNING THE RETREATING ARCTIC AIR MASS. PERIODS OF SNOW SHOWERS OR LIGHT SNOW ARE POSSIBLE THROUGH MID WEEK AS SEVERAL WAVES RIPPLE ALONG THE OLD FRONT. A LOT OF MODEL SPREAD AT THIS TIME LEAVES ME HESITANT TO TOUCH THE CURRENT EXTENDED POPS AND WX AS TIMING WILL BECOME MORE CERTAIN IN THE COMING DAYS. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... AIRFLOW AROUND HIGH PRESSURE CENTERED OVER KY THIS EVE WILL BRING CONTINUED VFR CONDS OVERNIGHT INTO FRI MORNING OVER MUCH OF CENTRAL PA...WITH GENERALLY CLEAR SKIES OVERNIGHT AND LIGHT W TO SWRLY WINDS. WEAK UPSLOPE COULD ADVECT LOW CLOUDS/MVFR CIGS INTO THE FAR WRN MTNS FROM THE SOUTHWEST TOWARDS MIDNIGHT...BUT THE MOISTURE OVER SRN OH AND WV IS RATHER SHALLOW ATTM. MIXING AND THE ATTEMPT TO MOVE INTO THE SUBSIDENCE OF THE RIDGE SHOULD BREAK THESE UP SIGNIFICANTLY...BUT LATEST SATELLITE PIX SHOWS AREA LOW CLOUDS PERSISTING OVER SRN OH. THUS HAVE INCLUDED BKN030 TO BFD AND JST FOR 03-12Z. STARTING LATER TOMORROW...TWO FEATURES WILL PUT A SQUEEZE ON THE REGION. FIRST...A WEAK WAVE OF LOW PRESSURE WILL MOVE ACROSS THE CENTRAL APPALACHIANS FRIDAY NIGHT AND CREATE LIGHT SNOW AND LOW CIGS FRIDAY NIGHT OVER THE SRN THIRD OF THE AREA...MAINLY IN MDT AND LNS. THE SECOND FEATURE IS A STRONG COLD FRONT WHICH WILL BRING SNOW SHOWERS AND SQUALLS LATE FRIDAY NIGHT AND EARLY SAT MORNING TO THE NW HALF OF THE AREA. EXPECT GUSTY WINDS...VERY LOW VSBYS AND CIGS IN THE NW HALF /BFD- JST/ BETWEEN 03 AND 12Z SAT. LOW CIGS AND VSBYS ARE ALSO POSSIBLE AT IPT-UNV- AOO AS WELL - MAINLY SAT MORNING WITHIN 3-4 HRS OF 12Z. OUTLOOK... SAT AFTN-SUN...MVFR/OCNL IFR NW IN SHSN. VFR ELSEWHERE. MON-TUE...VFR. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DANGELO/MARTIN NEAR TERM...DEVOIR/FITZGERALD SHORT TERM...DANGELO/FITZGERALD LONG TERM...DEVOIR/MARTIN AVIATION...DANGELO/GARTNER