EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 129 AM EST SUN NOV 30 2014 VALID 12Z WED DEC 03 2014 - 12Z SUN DEC 07 2014 ...OVERVIEW... ACTIVE UPPER-LEVEL FLOW PATTERN WITH PACIFIC ORIGINS IS ANTICIPATED TO BRING PERIODS OF PRECIPITATION TO THE WEST COAST AND GREAT BASIN. SYSTEMS MIGRATING ACROSS THE ROCKIES...AND DOWNSTREAM INTO THE EASTERN THIRD OF THE NATION WILL HAVE LOCALIZED SENSIBLE WEATHER IMPACTS---WITH TWO DISTINCT BRANCHES OF THE PACIFIC UPPER-LEVEL FLOW PATTERN MIGRATING INTO THE WESTERN ATLANTIC. THE NORTHERN BRANCH STREAKING FROM MONTANA TO THE NEW JERSEY COAST---PRODUCING LESS PRECIPITATION THAN ITS SOUTHERN COUNTERPART---RACING ACROSS THE UPPER RIO GRANDE...AND EASTWARD TO THE CAROLINAS. ...UNCERTAINTY ASSESSMENT... NOT MUCH DIFFERENCE IN THE MASS FIELDS BETWEEN THE 29/12Z NAEFS...GEFS AND ECENS MEANS THROUGH DAY 5---WITH THE GFS DETERMINISTIC RUN TAKING A SLIGHTLY MORE SOUTHERN ROUTE INTO THE WEST COAST VERSUS THE ECMWF/CANADIAN. BY 4/12Z...ALL 3 HAVE A DISCERNIBLE 850-500MB SHORTWAVE MIGRATING ACROSS CENTRAL WYOMING WITH A DOWNSTREAM TRAIL OF 500MB VORTICITY AND MID-LEVEL CLOUDINESS STREAKING OVER THE OHIO VALLEY TO THE DELMARVA. ALL THINGS CONSIDERED...THE AGREEMENT---THIS 12Z FORECAST CYCLE---WAS VERY GOOD. EXTEND THIS OUT ANOTHER 24 HOURS---TO 5/12Z---AND THE CONTINUITY REMAINS REASONABLE...WITH A JET STREAK MOVING ACROSS THE SOUTHERN PLAINS AND INTO THE SOUTHEAST---A DAY BEHIND THE AFOREMENTIONED MID-LEVEL WAVE. AFTER 5/12Z...THE QUESTION BECOMES ONE OF PREFERENCE. THE ECMWF APPEARS TO DRAW MORE EMPHASIS OUT OF THE NORTHERN STREAM AND BECOMES A MORE AMPLIFIED SOLUTION INVOF THE HUDSON VALLEY---A CLOSED 500MB LOW---AND MORE AMPLIFIED IN THE ALASKA PANHANDLE. THE CANADIAN AND GFS---EMPHASIZING THE SOUTHERN STREAM---WITH A DIGGING SYSTEM IN THE LOWER COLORADO BASIN AND SOUTHERN CALIFORNIA---AND MORE OF AN OPEN-WAVE TYPE SOLUTION IN THE NORTHEAST. ACTUALLY...IF THERE IS A REGION OF THE COUNTRY WHERE THINGS IN THE FORECAST MAY REQUIRE ALTERATIONS---IN THE FUTURE---I WOULD THINK THE SOUTHERN PLAINS WOULD BE IT. A DEEPER THAN 'CURRENTLY-PROGGED' SET OF DISTURBANCES MOVING ACROSS THE LOWER 48 IN THIS SOUTHERN BRANCH WOULD HAVE 'MORE ROOM' TO TRACK NORTHEASTWARD...THAN IS CURRENTLY ANTICIPATED IN THIS FAST PACIFIC FLOW. ...MODEL PREFERENCES... I BLENDED THE 29/12Z ECENS...NAEFS AND GEFS. FOR DAYS 3-4...THE DETERMINISTIC 29/18Z GFS AND 29/12Z ECMWF WERE INCORPORATED INTO THE NATIONAL TEMPS/POPS GRAPHICS---THOUGH THE 29/12Z CANADIAN WAS JUST AS REASONABLE...EVEN INTO DAY 5...SPLITTING THE DIFFERENCE OVER THE GREAT LAKES AND ACROSS THE CENTRAL GREAT BASIN. FOR DAY 6-7...AM NOT SURE THE ECMWF HAS THE RIGHT IDEA IN THE EASTERN PACIFIC ALONG AND SOUTH OF 42N LATITUDE. IN THIS FAST-ZONAL FLOW AND EMERGING WESTERN PACIFIC WAVE TRAIN---IT HAS NOT QUITE HANDLED THE SHEARING OF SYSTEMS---AND THEIR EAST-SOUTHEASTWARD PROGRESSION---QUITE THE WAY THE GFS HAS HANDLED THE FLOW AND SHEAR---ESPECIALLY EAST OF 160W LONGITUDE FROM THE ALEUTIANS TO THE HAWAIIAN ISLANDS. ALTHOUGH I MIGHT EXPECT A SOUTHWEST FLOW ALOFT BETWEEN 140W-160W AT THE 500MB LEVEL TO BRING SOME STABILITY TO THE ATMOSPHERE---A SHORTWAVE RIDGE PATTERN---THE FLOW ABOVE AND BELOW THIS LEVEL---CONTINUES TO DISPLAY 'VERTICALLY-DEEP'...FULL-LATITUDE WESTERLIES. SUSPECT THE BREAKS IN PRECIPITATION WILL BE SHORT-LIVED---ON THE WEST COAST AND WEST OF THE DIVIDE. ...SENSIBLE WEATHER HIGHLIGHTS... THE SOUTHERN BRANCH JET WILL BE ACTIVE...AS THE PACIFIC TROUGH BEGINS TO MIGRATE INTO THE SOUTHERN ROCKIES AND SOUTHERN HIGH PLAINS---AROUND DAY 4 AND A RELATIVELY-MOIST MID-LEVEL FLOW ATTEMPTS TO TAP THE NORTHWEST GULF AND STREAK ATOP A RATHER STABLE SURFACE RIDGE IN THE APPALACHIANS AND COASTAL PLAINS---DAYS 5-6. A SERIES OF FAST-MOVING PACIFIC WAVES WILL MIGRATE ACROSS THE NORTHERN PLAINS...GREAT LAKES AND NEW ENGLAND...AND GENERATE SOME PRECIPITATION AND SENSIBLE TEMPERATURES CHANGES AHEAD AND BEHIND THEM. THE OVERALL TRENDS WILL BE FOR SOME WARMING AHEAD...BUT THEN A RENEWED...CANADIAN CHILL. VOJTESAK