Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 072340 AFDCTP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE STATE COLLEGE PA 640 PM EST SUN FEB 7 2016 .SYNOPSIS... A SLOW MOVING AND DEEPENING UPPER TROUGH WILL SLIDE SOUTHEAST FROM THE UPPER GREAT LAKES. A LONG-DURATION PERIOD OF SNOW WILL LIKELY RESULT IN A WIDESPREAD LIGHT TO MODERATE ACCUMULATION FOR MUCH OF CENTRAL PA MONDAY INTO WEDNESDAY. LAKE EFFECT AND UPSLOPE SNOW SHOWERS WILL CONTINUE THROUGH THE END OF THE WEEK WITH ADDITIONAL ACCUMULATION LIKELY IN THE FAVORED NORTHWEST SNOWBELT AND HIGHER TERRAIN ALONG THE ALLEGHENIES AND LAURELS. A MUCH COLDER WEATHER PATTERN IS EXPECTED BY LATER IN THE WEEK WITH A BLAST OF ARCTIC AIR FOR VALENTINES WEEKEND. && .NEAR TERM /THROUGH MONDAY/... SATL TRENDS AND MDL DATA SUPPORT MCLEAR SKIES AND A NEARLY CALM WIND THIS EVENING FOR MUCH OF CENTRAL PA. SOME THICKER CIRRUS ASSOC WITH WESTERN PERIPHERY OF COASTAL STORM WILL AFFECT THE SE COUNTIES. EXPECT INCREASING CLOUD COVER EARLY MONDAY MORNING ACROSS THE WESTERN COUNTIES IN ADVANCE OF UPPER LOW SINKING SE ACROSS THE GRT LKS. MDL CONSENSUS INDICATES IT WILL BE A RELATIVELY MILD NIGHT WITH LOWS IN THE MID TO UPPER 20S IN MOST AREAS. SOME OF THE NORMALLY COLDER VALLEYS WILL NO DOUBT DIP TO ARND 20F...ESP ACROSS PARTS OF THE LOWER SUSQ VALLEY...WHERE SNOW COVER REMAINS. THE SQUEEZE PLAY IS ON FOR MONDAY ACROSS THE REGION...AS A POWERFUL 976 MB SFC LOW MOVES NE...WELL TO THE SOUTH OF LONG ISLAND AND CAPE COD...WHILE A SLOW-MOVING AND AMPLIFYING UPPER TROUGH TAKES ON A NEGATIVE TILT ACROSS THE MID ATLANTIC REGION LATE MONDAY/MONDAY NIGHT. DUAL...TO MULTI-LAYERED CLOUDS WILL GRADUALLY LOWER/THICKEN UP FROM THE WEST AND SOUTH DURING THE DAY...WITH OVC SKIES BY LATE AFTERNOON IN ALL AREAS BUT PERHAPS THE SUSQ VALLEY AND POINTS JUST TO THE EAST. WET BULB ZERO ELEVATION CLOSE TO THE SFC PAINTS A SNOW...RATHER THAN RAIN/SNOW MIX IN MOST PLACES LATER MONDAY AFTERNOON/EVENING...EXCEPT FOR PERHAPS THE SUSQ VALLEY AT OR BELOW 900 FT MSL. LATEST SREF AND NAM ARE IN DECENT AGREEMENT WITH THE ONSET TIME OF THE SNOW - LATE IN THE AFTERNOON ACROSS THE LAURELS...WHILE THE GEFS MEAN IS 2-3 HOURS SLOWER. A COATING TO LESS THAN ONE INCH OF SNOW IS POSSIBLE ACROSS THE SW THIRD OF THE CWA BY MONDAY EVENING /BUT MAINLY AT ELEVATIONS 1500 FT MSL AND HIGHER SINCE HIGH TEMPS PRIOR TO THE PRECIP BEGINNING WILL BE IN THE U30S TO L40S. IT IS FAIRLY CERTAIN CENTRAL PA WILL EXPERIENCE A PROLONGED PERIOD OF LIGHT...POSSIBLY MODERATE SNOW /IN ONE OR TWO SLOW MOVING AND RATHER NARROW FGEN BANDS/ DURING THE MONDAY NIGHT THROUGH TUESDAY PERIOD OF THE FORECAST. LATEST MDL GUIDANCE SUGGESTS THE STEADIEST/HEAVIEST SNOW WILL ACCOMPANY THE PASSAGE OF SHORTWAVES MON EVENING AND DURING DURING THE DAYLIGHT HRS OF TUESDAY...WITH A POSSIBLE LULL IN THE PRECIP TUE AM. THE LONG DURATION AND LIGHT TO MODERATE AMOUNTS EXPECTED DON/T FALL INTO OUR WATCH/WARNING CRITERIA AT THIS POINT IN TIME...AND ARE ONLY NEAR THE THRESHOLD OF OUR WINTER WEATHER ADVISORIES OF 3 INCHES/12 HOURS /2 INCHES/12 HOURS ACROSS THE LOWER SUSQ BEGINNING THIS PAST FALL/. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... A WELL-DEFINED UPPER TROUGH/CIRCULATION OVER THE ARROWHEAD OF MN THIS AFTERNOON WILL GRADUALLY PHASE-IN ADDITIONAL SHORTWAVE ENERGY AS IT DIGS SOUTHEAST THROUGH THE GREAT LAKES...EVOLVING INTO A CLOSED LOW WITHIN A BROAD/ANOMALOUS MEAN TROUGH MIGRATING SLOWLY FROM THE OHIO VALLEY INTO THE NORTHEAST STATES THROUGH MIDWEEK. THE COMPLEX EVOLUTION/AMPLIFICATION OF THE LARGE SCALE TROUGH CHARACTERIZED BY SEVERAL EMBEDDED SHORTWAVE DISTURBANCES CONTINUES TO RESULT IN A COMPLICATED/LOWER CONFIDENCE SNOWFALL FORECAST. DESPITE DECENT AGREEMENT ON THE OVERALL PATTERN...THERE IS STILL A SOME SPREAD REGARDING IMPORTANT DETAILS SUCH AS THE QPF PLACEMENT AND LOCATION OF SNOW AMOUNTS. THERE MAY ALSO BE BOUNDARY LAYER TEMPERATURE ISSUES THAT INTRODUCE FURTHER COMPLEXITY TO AN ALREADY CHALLENGING SNOW FCST. IN THIS KIND OF FORECAST DILEMMA WITH VARYING MODEL SIMULATIONS AND SMALL SCALE DIFFERENCES...WE CONTINUED TO EMPLOY A RELATIVELY CONSERVATIVE STRATEGY FOR FCST SNOW AMOUNTS BY INCREMENTALLY NUDGING TOWARD A MULTI-MODEL CONSENSUS AND WPC WINTER WEATHER GUIDANCE. WHAT WE DO KNOW IS THAT A PROLONGED PERIOD OF SNOW IS LIKELY FROM MONDAY NIGHT THROUGH TUESDAY...FOLLOWED BY A TRANSITION TOWARD A LAKE EFFECT/UPSLOPE SNOW PATTERN INTO WEDNESDAY. THE STORM TOTAL SNOWFALL COMPILED OVER A 48-60 HOUR PERIOD SHOWS A BROAD AREA OF 3+ INCHES WITH HIGHER AMOUNTS SHADED TOWARD THE WESTERN AND SOUTHERN PORTIONS OF THE AREA. THE MAXIMUM FCST SNOW AMOUNTS AT THIS TIME ARE FOCUSED OVER THE HIGHER TERRAIN IN SOMERSET COUNTY. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... ANOMALOUS WESTERN US RIDGE/EASTERN US TROUGH PATTERN WILL BE IN PLACE THROUGH MID WEEK. THE GLOBAL ENSEMBLE MEANS GENERALLY KEEP THIS PATTERN CONFIGURATION INTACT INTO THE WEEKEND BUT AT A SLIGHTLY DECREASING AMPLITUDE..ESPECIALLY THE WESTERN US RIDGE. AS THE BROAD UPPER LEVEL CIRCULATION DEPARTS OVER THE NORTHEAST TOWARD THE END OF THE WEEK...THE GLOBAL MODELS SHOW IT BEING REPLACED BY A POLAR VORTEX DROPPING SOUTH FROM THE ARCTIC. COLD AIR WILL BEGIN SPILLING SOUTHWARD FROM CANADA LATER IN THE WEEK REINFORCED INITIALLY BY A SECONDARY FRONT ON THURSDAY...FOLLOWED BY A SIGNIFICANT ARCTIC AIR INTRUSION FOR VALENTINE`S WEEKEND. RESIDUAL SNOWS ASSOCIATED WITH THE UPPER TROUGH ON WED SHOULD TRANSITION TOWARD LAKE EFFECT/UPSLOPE FOR SEVERAL DAYS THU-SAT WITH ADDITIONAL ACCUMULATION LKLY OVER THE FAVORED AREAS DOWNWIND OF LAKE ERIE AND IN THE HIGHER TERRAIN OF THE ALLEGHENIES/LAURELS. CONFIDENCE IS HIGH IN THE FCST COLD PATTERN WHICH SHOULD PEAK OVER THE WEEKEND. MAX/MIN TEMPERATURE DEPARTURES OF 20 DEGREES BELOW CLIMO ARE PROBABLE SAT-SUN. WIDESPREAD SUB ZERO WIND CHILLS APPEAR LIKELY SATURDAY NIGHT INTO EARLY SUNDAY...WITH PROJECTED MINIMUM WC VALUES BETWEEN -10 TO -25 DEGREES BELOW ZERO. && .AVIATION /23Z SUNDAY THROUGH FRIDAY/... HIGH PRESSURE OVER THE AREA WILL RESULT IN AREAS OF MAINLY HIGH CLDS LATE TODAY AND TONIGHT...THOUGH THE SOUTHEAST TAF SITES. /KLNS AND KMDT/ WILL SEE A THICKER SHIELD OF CIRROSTRATUS FROM THE NW EDGE OF AN INTENSIFYING WRN ATLANTIC SFC LOW. SOME MID-LEVEL ALTO CU WILL SPREAD OVER THE WRN PENN TAF SITES LATER TONIGHT/MONDAY MORNING...BEFORE LOWERING TO BORDERLINE MVFR THERE MONDAY AFTERNOON. A COMPLEX WEATHER PATTERN MAY RESULT IN SOME SNOW AND COLDER TEMPERATURES AFTER TODAY AS A DEEP UPPER TROUGH BECOMES CARVER OUT OVER THE EASTERN U.S. OUTLOOK... MON...PM LGT SNOW POSSIBLE MID TO LATE AFTERNOON...MAINLY ACROSS THE W MTNS /KJST AND KBFD/. MON NIGHT AND TUE...LGT SNOW LIKELY...ESP CENTRAL AND WRN MTNS. WED...IFR/MVFR IN SHSN WRN AIRSPACE. MVFR-VFR CIGS CENTRAL/EAST. SFC WIND GUSTS 20+KT FROM 270-300. THU AND FRIDAY...MVFR IN -SHSN POSSIBLE W MTNS. && .CTP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...STEINBUGL NEAR TERM...FITZGERALD/LAMBERT SHORT TERM...STEINBUGL LONG TERM...STEINBUGL AVIATION...LAMBERT

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