Prognostic Meteorological Discussion
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000 FXUS02 KWBC 281544 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1143 AM EDT WED SEP 28 2016 VALID 12Z SAT OCT 01 2016 - 12Z WED OCT 05 2016 ...PATTERN OVERVIEW AND UNCERTAINTY ASSESSMENT... A CUTOFF UPPER-LEVEL LOW IS FORECAST BY ALL GUIDANCE TO BE IN PLACE ACROSS THE OHIO VALLEY AT THE BEGINNING OF DAY 3 /12Z SAT, WHICH WILL THEN LIFT SLOWLY NORTH AND EASTWARD AS IT WEAKENS. FARTHER WEST, A SECOND UPPER LOW IS FORECAST TO BE CENTERED JUST OFF THE BRITISH COLUMBIA COAST, WITH SHORTWAVE ENERGY TO ITS SOUTH MOVING INTO NORTHERN CA/THE PAC NW. IN BETWEEN THESE TWO FEATURES, UPPER-LEVEL RIDGING IS FORECAST TO EXTEND NORTH FROM MEXICO INTO THE PLAINS. FORECAST UNCERTAINTY IN THE LARGE SCALE PATTERN IS INITIALLY RELATIVELY LOW ON DAYS 3 AND 4, WITH MODEL SPREAD INCREASING SUBSTANTIALLY IN THE DAY 5-7 TIME FRAME. THE EXACT EVOLUTION OF THE LARGE SCALE PATTERN ACROSS NORTH AMERICA AND THE NORTH ATLANTIC OCEAN WILL AFFECT THE EVENTUAL TRACK OF WHAT IS FORECAST BY THE NATIONAL HURRICANE CENTER TO BE HURRICANE MATTHEW. A BLEND OF THE 00Z GFS/GEFS MEAN/ECMWF ENS MEAN WAS USED FOR THE WPC MEDIUM RANGE FORECAST. THE 00Z DETERMINISTIC ECMWF BECOMES AN APPARENT OUTLIER SOLUTION WITH RESPECT TO THE EVOLUTION OF THE PATTERN ACROSS THE NORTHEASTERN U.S./NORTH ATLANTIC BY DAYS 6-7, KEEPING THE UPPER LOW INTACT AND FARTHER WEST MUCH LONGER THAN ANY OTHER DETERMINISTIC SOLUTION AS WELL AS THE 00Z EC ENS MEAN, THUS THIS SOLUTION WAS NOT INCLUDED IN THE BLEND. THE OFFICIAL FORECAST TRACK FROM THE NATIONAL HURRICANE CENTER FOR MATTHEW SEEMS TO FIT A COMPROMISE BETWEEN THE GFS/GEFS AND ECMWF/ECMWF ENSEMBLE SOLUTIONS. FARTHER WEST, SPREAD ALSO INCREASES FAIRLY SUBSTANTIALLY FROM DAY 5 ONWARD, PRIMARILY WITH RESPECT TO THE PROGRESSION OF THE TROUGH/UPPER LOW THAT EVOLVES ACROSS THE WESTERN U.S. THE AFOREMENTIONED BLEND APPEARS TO REPRESENT A GOOD MIDDLE GROUND SOLUTION ACROSS THE WEST AS WELL, BETWEEN THE QUICKER GFS/GEFS AND THE SLOWER ECMWF/ECMWF ENSEMBLE MEAN. THIS BLEND HOLDS THROUGH DAYS 6-7 AS THE SYSTEM MOVES INTO THE CENTRAL U.S. ...SENSIBLE WEATHER HIGHLIGHTS... THE PERSISTENT UPPER LOW INITIALLY ACROSS THE OHIO VALLEY WILL SUPPORT CONTINUED SHOWER ACTIVITY ALONG PORTIONS OF THE EAST COAST, GREAT LAKES, AND NORTHEAST ON SATURDAY AND SUNDAY. AFTER THAT TIME ALL EYES ON THE EASTERN SEABOARD WILL TURN TO THE POSSIBLE IMPACTS FROM MATTHEW. PLEASE REFER TO PRODUCTS ISSUED BY THE NATIONAL HURRICANE CENTER FOR THE OFFICIAL FORECAST TRACK FOR MATTHEW. DEPENDING ON THE EXACT TRACK, SOME POTENTIAL IMPACTS SUCH AS AS HIGH SURF, HEAVY RAIN AND STRONG WINDS COULD BEGIN TO AFFECT THE EASTERN SEABOARD DURING THE MEDIUM RANGE FORECAST PERIOD. ACROSS THE WEST, THE LARGE TROUGH/UPPER-LOW FORECAST TO EVOLVE DURING THE MEDIUM RANGE WILL SUPPORT AREAS OF PRECIPITATION AND GUSTY WINDS, ALONG WITH GRADUALLY LOWERING SNOW LEVELS DURING THE SUNDAY TO TUESDAY TIME PERIOD. AS THE SYSTEM MOVES INTO THE CENTRAL U.S. LATE IN THE MEDIUM RANGE, AND SURFACE LOW PRESSURE DEVELOPS ACROSS THE NORTHERN PLAINS, GOOD INFLOW OF MOISTURE AND A STATIONARY FRONTAL BOUNDARY NORTHEAST OF THE SURFACE LOW COULD SUPPORT PERIODS OF SHOWERS AND THUNDERSTORMS, WITH SOME POTENTIAL FOR HEAVY RAINFALL AMOUNTS. RYAN $$

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