Displaying AFOS PIL: PMDEPD Received: 2016-01-19 16:00 UTC
092 FXUS02 KWBC 191601 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1100 AM EST TUE JAN 19 2016 VALID 12Z FRI JAN 22 2016 - 12Z TUE JAN 26 2016 HIGHLIGHTS... LETS CUT TO THE CHASE. THE MAIN EVENT IN THE MEDIUM RANGE IS THE POTENTIAL FOR A SIGNIFICANT EAST COAST SNOWSTORM FROM FRIDAY THROUGH SUNDAY/DAYS 3 TO 5. THERE HAS BEEN AND CONTINUES TO BE RELATIVELY GOOD AGREEMENT ESPECIALLY BETWEEN THE MODEL ENSEMBLES. COMPARING THE OPERATIONAL RUNS TO THE ENSEMBLE MEANS DOES INDICATE SOME DIFFERENCES THAT ARE SMALL IN THE LARGE SCALE BUT CRUCIAL TO THE FORECAST. ALL MODELS SUGGEST THAT MAJOR DEVELOPMENT FOR THIS SYSTEM WILL OCCUR AS IT MOVES TO THE MID ATLANTIC COAST AND THEN THE SYSTEM OCCLUDES...BECOMES MORE VERTICAL AND THEN CONTINUES NORTHEASTWARD WITH THE MOVEMENT OF THE UPPER TROUGH. WITH THAT IN MIND...THE STORM WILL LIKELY SLOW IN ITS FORWARD MOVEMENT AS IT MOVES OFF THE MID ATLANTIC COAST AND THEN WILL LIKELY ACCELERATE NORTHEASTWARD OR ANOTHER TRIPLE POINT LOW MAY DEVELOP FARTHER NORTH AND EAST. THE 00Z ECMWF SUGGESTS BOTH SCENARIOS. IN EITHER EVEN...THE OVERALL SPEED OF THE SYSTEM IS IMPORTANT TO AFFECT THE AMOUNT OF SNOW IN ANY ONE AREA. THIS WILL BE AN IMPORTANT TREND TO FOLLOW AS THE MORNING MODEL SOLUTIONS START COMING IN. IN ADDITION...ANY TRENDS EITHER NORTH OR SOUTH WILL IMPACT SNOWFALL AMOUNTS ALONG THE NORTHERN EDGE OF THE HEAVIEST SNOW AS WELL AS THE ISSUES OF MIXING/CHANGEOVER ALONG THE SOUTHERN EDGE OF THE SYSTEM. THERE HAVE BEEN SUBTLE NORTH/SOUTH SHIFTS WITH THIS FORECAST BUT WILL HAVE TO BE ASSESSED WHEN THE MORNING MODELS ARRIVE. THERE HAVEN'T BEEN LARGE CHANGES WITH THE OVERNIGHT CYCLE. IN GENERAL...THE OPERATIONAL GFS RUNS ARE SLIGHTLY MORE PROGRESSIVE THAN THE OPERATIONAL ECMWF RUNS. IN PARTICULAR THE 06Z GFS TRENDED FASTER THAN PREVIOUS RUNS RESULTING IN LOWER SNOWFALL AMOUNTS DUE TO LOWER SNOWFALL DURATION. THE 00Z UKMET IS SIMILAR TO THE ECMWF AND TO SOME EXTENT THE GFS BUT THE 00Z CANADIAN WAS MUCH MORE PROGESSIVE THAN ANY OTHER MODEL AS WELL AS THE CANADIAN ENSEMBLES. AS A RESULT...LATER IN THE FORECAST...THE NAEFS MEAN IS FASTER THAN THE GFS MEAN DUE TO THE CONTRIBUTION OF THE CANADIAN SOLUTIONS. AT THIS TIME...THE HIGHEST PROBABILITIES FOR THE HEAVIEST SNOW BETWEEN THE ISSUES WITH THE NORTHERN EDGE AND THE SOUTHERN MIX/CHANGEOVER IS CURRENTLY SUGGESTED TO RUN FROM NORTHERN VIRGINIA TO EASTERN PENNSYLVANIA/NEW JERSEY INTO SOUTHERN NEW ENGLAND. TO PUT THIS SYSTEM IN CONTEXT...THE POTENTIAL SNOWFALL DISTRIBUTION HAS SIMILARITIES TO SEVERAL MAJOR EAST COAST STORMS IN RECENT PAST INCLUDING THE 5-6 FEBRUARY 2010 SNOWSTORM/THE JANUARY 1996 BLIZZARD OF 1996 AND THE PRESIDENTS DAY OF FEBRUARY 2003. JANUARY 1996 IS LIKELY TO BE MORE WIDESPREAD/HEAVY BUT ONLY TIME WILL TELL. THE MECHANISMS COMING TOGETHER FOR A MAJOR SNOWFALL ARE TEXTBOOK. IN THE WEST...PRECIPITATION SHOULD WANE ALONG THE COAST DAY 3 INTO DAY 4...WITH THE NEXT MAJOR PRECIPITATION EVENT EXPECTED ACROSS THE PACIFIC NORTHWEST BY NEXT MONDAY OR TUESDAY...WITH SEVERAL INCHES OF LIQUID EQUIVALENT EXPECTED. CONFIDENCE... THIS IS A HIGH CONFIDENCE EVENT THIS FAR OUT IN ADVANCE BUT THAT ALSO SUGGEST THAT SMALL CHANGES CAN HAVE SIGNIFICANT CHANGES TO IMPACT. THERE IS STILL 3 TO 4 DAYS FROM THE EVENT AND MANY MODEL SOLUTIONS TO COME. THERE HAS BEEN EXCELLENT CONTINUITY RELATIVE TO AVERAGE AND PERHAPS SIMILAR TO WHAT WAS OBSERVED WITH THE FORECASTS PRIOR TO 5-6 FEBRUARY 2003...WHICH WAS FORECAST AS MUCH AS 8 DAYS IN ADVANCE. OTHER STORMS HAVE BEEN MUCH LESS PREDICTABLE. THIS MAY BE ONE CASE WITH A HIGH DEGREE OF PREDICTABILITY BUT WE SHALL SEE. KOCIN $$