Area Forecast Discussion
Issued by NWS State College, PA

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109 FXUS61 KCTP 091817 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 117 PM EST TUE FEB 9 2016 .SYNOPSIS... AN UPPER LOW WILL MOVE INTO THE REGION FROM THE OHIO VALLEY AND TRANSITION INTO A LONG WAVE TROUGH. AN ONGOING WIDESPREAD LIGHT TO MODERATE SNOW WILL TAPER OFF THIS EVENING. LAKE EFFECT AND UPSLOPE SNOW SHOWERS WILL FOLLOW FOR MID-WEEK INTO THE FIRST PART OF THE WEEKEND...WHERE ADDITIONAL ACCUMULATIONS ARE LIKELY IN THE FAVORED NORTHWEST SNOWBELT AND HIGHER TERRAIN ALONG THE ALLEGHENIES AND LAURELS. THE COLDEST AIRMASS OF THE WINTER IS POISED TO BRING FRIGID TEMPERATURES AND DANGEROUS WIND CHILLS FOR VALENTINES WEEKEND. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1230PM UPDATE... BANDS OF MODERATE SNOW CONTINUE TO IMPACT THE LOWER SUSQ WHERE RATES IN HIGHEST RADAR RETURNS ARE RUNNING AROUND AN INCH/HOUR. THIS WILL CONTINUE INTO MID/LATE AFTERNOON BEFORE DIMINISHING AS AREA OF SNOW DRIFTS EASTWARD...WITH ONLY LIGHT ACCUMS LINGERING INTO THE EVENING HOURS. ELSEWHERE...HRRR HAS BEEN HINTING AT A N-S ORIENTED BAND OF SNOW DEVELOPING OVER THE WESTERN HIGHER TERRAIN...WHICH IS FORMING AS I TYPE. THIS BAND COULD BRING A SHORT PERIOD OF MODERATE SNOW TO WESTERN/CENTRAL AREAS BUT OVERALL ACCUMS WILL NOT ADD UP TO MUCH. OVER THE LAURELS...PERSISTENT LIGHT SNOW WILL CONTINUE TO GRADUALLY ACCUMULATE THROUGH THE AFTERNOON. TEMPS BASICALLY STEADY THIS AFTERNOON BEFORE FALLING INTO THE UPPER 20S THIS EVENING. 630 AM UPDATE... FINALLY SNOWING OUT THE WINDOW BUT NO ACCUM YET - EVEN ON THE CARS. MCV-LIKE FEATURE EASY TO PICK OUT ON THE IR LOOP THIS MORNING OVER WV. THIS FEATURE WILL SLIDE INTO THE STATE FROM THE SW. THE FORCING AHEAD OF IT IS ALREADY BEGINNING TO CREATE A COHERENT AREA OF LIGHT SNOW. RADAR RETURNS GRADUALLY INCREASING IN THE LAST FEW FRAMES AND SPREADING NORTHWARD FROM WV/MD. WORST OF THE VSBYS ARE KHGR AND KMDT - BUT THEY ARE >1SM AT THIS TIME. WILL CONTINUE TO RIDE THE FCST AS IS...ALLOWING THE SNOW TO FALL FOR A WHILE BEFORE TAKING ANY FURTHER ACTION. PREV... LOTS OF DECISIONS THIS MORNING WITH THE OVERWHELMING MESSAGE ONE OF LOWER SNOWFALL NUMBERS. HAVE MADE ONE SMALL CHANGE TO THE FLAGS BY ADDING SCHUYLKILL COUNTY INTO THE ADVY. REASONING IS THAT THE TEMPERATURE PROFILE WILL FAVOR AN ELEVATION-DEPENDENT SNOWFALL. THE TEMPS IN THE VALLEYS WILL BE MARGINAL FOR EFFICIENT ACCUMULATIONS. HOWEVER...THE IN-CLOUD PROFILE AND TEMPS IN THE HIGHER ELEVATIONS DO FAVOR SOME 15:1 RATIOS DURING THE DAYLIGHT HOURS. SO...ARMED WITH THAT...HAVE DECIDED TO HOLD ONTO THE WARNING AND REST OF THE ADVYS AS IS FOR THE TIME-BEING. HAVE TRIED REALLY HARD TO KEEP ACCUMS IN THE WARNING RANGE - BUT HAVE CONFINED THEM TO THE HIGHER ELEVATIONS. IT WILL LIKELY WORK OUT THAT THE HILLTOPS IN THE WARNING-AREA COULD GET 5-7 INCHES WHILE THE CITIES AND LOWEST ELEVATIONS GET ONLY AN INCH OR TWO. THE DISORGANIZED LOOK TO THE FORCING WILL PROBABLY MEAN NO LONG-LIVED BANDING AND ONLY LIMITED TIMES OF 1 IN/HR RATES IF ANY AT ALL. QPF AMOUNTS LOOKING PRETTY TENUOUS AS WELL WITHOUT ANOMALOUS PWATS AND NO GOOD OFF-OCEAN/GULF FLOW TO TAP INTO ADDITIONAL HELP. WITH THE EXPECTED MELTING...WE ARE IN DANGER OF NOT MAKING WARNING NUMS - CERTAINLY IF WE TAKE INTO ACCOUNT THE 12-HR CRITERIA. SO MANY THINGS GOING AGAINST WARNING SNOW ACCUMS...BUT THE CAT IS OUT AND RUNNING AROUND ALREADY. SINCE WE ALREADY HAVE THE WARNING UP...HAVE CHOSEN TO GIVE IT A LITTLE MORE TIME FOR THE STORM TO SHOW IT/S HAND. RATHER NOT TAKE DOWN THE WARNING BEFORE IT EVEN HAS A CHANCE TO GET INTO THE PROGGED HEAVIEST PRECIPITATION. TIMING LOOKS LIKE THE SRN TIER WILL GET SOME STEADY SNOW THIS MORNING BUT THEN THE BEST FORCING SEEMS LIKE IT WILL BE OVER THE LAURELS THIS AFTERNOON AND SLIDE ACROSS THE CENTRAL MOUNTAINS AND OFF TO THE EAST THIS EVENING. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... UPPER LOW WILL BE FILLING AND LOSING IT/S CLOSED CONTOURS...BECOMING A LONG WAVE TROUGH TONIGHT. SNOW WILL PROBABLY BE SLIDING STEADILY TO THE EAST IN THE EVENING AND BE OFF TO THE EAST OF CENTRAL PA BY MIDNIGHT. THE HEIGHTS STILL LOWER SOME...THOUGH...AND SOME 1/2 TO 1 IN/HR RATES ARE POSSIBLE ALONG WHAT MAY TURN OUT TO BE A FRONTAL BAND AS THE BEST COLD AIR MOVES IN AT LOW LEVELS AND WINDS PICK UP FROM THE WEST. THINGS THEN TRANSITION TO A PLAIN-OL UPSLOPE SNOW SITUATION FOR THE LAURELS. A LM CONNECTION DEVELOPS UNDER HIGHLY-FAVORABLE TEMPERATURES/CONDITIONS. THE AIR DOES DRY OUT ON THE WHOLE...SO MOST OTHER LOCATIONS WILL SEE LITTLE MORE THAN FLURRIES. DOWNSLOPE MAY ALLOW THE SE TO GET A DEG OR TWO WARMER THAN TODAY. THE LAKE EFFECT IN THE NW WILL BE RAMPING UP...BUT THE STACKED WEST WIND PROFILE FAVORS WRN NY STATE THAN NW PA. OF COURSE...THE COLD AIR WILL LIKELY EXTEND SOME BANDS INTO WARREN CO. HAVE CHOSEN TO HOLD OFF ON ANY LK EFF FLAGS FOR NOW - SINCE THE NEED FOR A WATCH/WARNING IS NOT QUITE 50PCT AND TIMING IS SUCH THAT THE CURRENT WIDESPREAD SNOW AND WARNS/ADVYS ELSEWHERE MAY BE CONFUSING. IT WILL BE COMPLICATED ENOUGH FOR THE LAURELS WHERE THE SNOW WILL NEVER REALLY TAKE A BREAK. TEMPS DROP OFF QUITE QUICKLY LATE WED. MINS MAY GET INTO THE SINGLE DIGITS ON THE HILL TOPS OF THE ALLEGHENIES AND LAURELS. WIND CHILLS WILL GO BELOW ZERO. && .LONG TERM /THURSDAY THROUGH MONDAY/... *IMPACT WEATHER HIGHLIGHTS INCLUDE ADDITIONAL LAKE EFFECT AND UPSLOPE SNOW ACCUMULATIONS THURSDAY-SATURDAY...FOLLOWED BY FRIGID TEMPERATURES AND DANGEROUSLY COLD WIND CHILLS FOR VALENTINES WEEKEND. ANOMALOUS WESTERN RIDGE/EASTERN TROUGH PATTERN WILL REMAIN IN PLACE THROUGH THE WEEKEND. THE GLOBAL ENSEMBLE MEANS GENERALLY KEEP THIS PATTERN CONFIGURATION INTACT INTO NEXT WEEK BUT AT A DECREASING AMPLITUDE. AS THE BROAD UPPER LEVEL CIRCULATION DEPARTS OVER THE NORTHEAST TOWARD THE END OF THE WEEK...IT WILL BE REPLACED BY A POLAR VORTEX DROPPING SOUTH ACROSS HUDSON BAY INTO SE CANADA. COLD AIR WILL BEGIN SPILLING SOUTHWARD LATER IN THE WEEK...REINFORCED INITIALLY BY A SECONDARY FRONT ON THURSDAY. CONFIDENCE CONTINUES TO INCREASE IN A SIGNIFICANT ARCTIC AIR INTRUSION/COLD OUTBREAK FOR VALENTINE`S WEEKEND. LAKE EFFECT/UPSLOPE SNOWS FOR SEVERAL DAYS THU-SAT WILL BRING ADDITIONAL LGT-MDT ACCUMULATION OVER THE FAVORED NORTHWEST SNOWBELT DOWNWIND OF LAKE ERIE AND IN THE HIGHER TERRAIN OF THE ALLEGHENIES/LAURELS. A NEW ELEMENT IN THE FCST IS DEVELOPING LOW PRESSURE OFF THE MID-ATLANTIC/NORTHEAST COAST BY EARLY SATURDAY. AT THIS TIME THE 08/00Z ECMWF LIES ON THE WESTERN EDGE OF THE GUIDANCE ENVELOPE. CONFIDENCE IS HIGH IN THE FCST COLD PATTERN/WELL-BELOW NORMAL TEMPERATURES THROUGH THE PERIOD. THE COLDEST AIRMASS OF THE WINTER APPEARS POISED TO ARRIVE THIS WEEKEND WITH GFS/EC BOTH BRINGING -30C AIR AT 850MB INTO PA. MAX/MIN TEMPERATURE DEPARTURES OF -20 TO -25 DEGREES BELOW CLIMO ARE PROBABLE SATURDAY AND SUNDAY. WIDESPREAD SINGLE DIGIT TEMPERATURES +/- ZERO ARE FCST SATURDAY NIGHT INTO EARLY SUNDAY. A STRONG GRADIENT BETWEEN LOW PRESSURE OFF THE NEW ENGLAND COAST AND 1040+MB ARCTIC HIGH DROPPING INTO THE UPPER MS VALLEY WILL PRODUCE GUSTY WINDS AND DANGEROUSLY COLD WIND CHILLS -10F TO -25F DEGREES BELOW ZERO. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... IFR/LIFR CONDITIONS WILL REMAIN WIDESPREAD...ESP SOUTH OF I-80...AS LIGHT TO MODERATE SNOW EVENT CONTINUES THIS AFTERNOON. IMPROVEMENT EXPECTED THIS EVENING...ESPECIALLY TO VSBY...AS SNOW TAPERS TO FLURRIES. CIGS WILL REMAIN LOW THROUGH THE EVENING...BUT AS WESTERLY FLOW INCREASES A BIT OVERNIGHT CIGS WILL IMPROVE AS WELL IN CENTRAL AND EASTERN AREAS. LOWER SUSQ WILL IMPROVE TO VFR WITH CENTRAL MTNS HOLDING ON TO AN MVFR DECK. WESTERN HIGHER TERRAIN WILL CONTINUE TO SEE SOME SNOWFLAKES IN THE AIR WITH UPSLOPE FLOW KEEPING MAINLY IFR CIGS IN PLACE. OUTLOOK... WED...MAINLY IFR IN SNOW WRN AIRSPACE. MVFR-VFR CIGS CENTRAL/EAST. THU-SAT...MVFR IN -SHSN W MTNS. VFR ELSEWHERE. SUN...NO SIG WX. && .CTP WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 1 AM EST WEDNESDAY FOR PAZ025>028-034>036-056>059-063. WINTER WEATHER ADVISORY UNTIL 7 PM EST WEDNESDAY FOR PAZ024- 033. WINTER STORM WARNING UNTIL 1 AM EST WEDNESDAY FOR PAZ064>066. && $$ SYNOPSIS...DANGELO/RXR NEAR TERM...DANGELO/RXR SHORT TERM...DANGELO LONG TERM...STEINBUGL AVIATION...RXR

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