EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1039 AM EST MON DEC 08 2014 VALID 12Z THU DEC 11 2014 - 12Z MON DEC 15 2014 ...SYNOPSIS... ENERGETIC FLOW ACROSS THE PACIFIC WILL HELP SHAPE TWO DEEP AND EASILY DEFINED MEDIUM WAVELENGTH TROUGHS WHICH WILL BRING PRECIPITATION TO CALIFORNIA AND MUCH OF THE WEST BEFORE SPLITTING AROUND A MORE BLOCKY PATTERN OVER CENTRAL AND EASTERN NORTH AMERICA. THE PRIMARY FEATURES OF INTEREST ON DAYS 3-7 ARE A LARGE AND CLOSED EASTERN U.S. CYCLONE THAT WILL DRIFT ONLY GRADUALLY INTO THE ATLANTIC...AND AN EASTERN PACIFIC TROUGH THAT SHOULD REACH THE PLAINS ALONG WITH AN UPSTREAM TROUGH THAT SHOULD APPROACH THE WEST COAST BY EARLY NEXT WEEK. ...MODEL EVALUATION... WITH WELL DEFINED AND LARGE SCALE TROUGHS ON THE MAP THE MODELS ARE IN GOOD AGREEMENT...WHILE DISPLAYING THEIR USUAL TENDENCIES...THE GFS/GEFS ON THE FAST SIDE...OPERATIONAL ECMWF AMONG THE SLOWEST AND DEEPEST SOLUTIONS...AND ECMWF ENSEMBLE MEAN LOOKING LIKE THE BEST COMPROMISE. FOR THE EASTERN U.S. CLOSED LOW WE FAVORED THE SLOWER SOLUTIONS WHICH KEEP THE SYSTEM CLOSED FOR GREATER DURATION. IT IS A ROBUST CYCLONE ONLY RECENTLY HAVING REACHED MATURITY AS OF DAY 3...AND THE MINOR HIGH-LATITUDE SHORTWAVES BRUSHING ACROSS IT THROUGH THE NORTHERN STREAM SHOULD NOT BE SO EFFECTIVE AS THE 00Z GFS/UKMET SUGGEST AT TUGGING THE LOW TO THE NORTH AND EAST. THE 06Z GFS WAS A SLIGHTLY BETTER OPTION IN THE EAST...AND SEEMED TO HANDLE THE PACIFIC TROUGHS WELL EXCEPT FOR BEING SLIGHTLY FAST BY DAY 7. STILL...FOR OUR MANUAL FORECAST WE PREFERRED TO BLEND NEARLY EVEN PERCENTAGES OF THE ECMWF AND ECMWF ENSEMBLE MEAN WITH A SMALL AMOUNT OF THE 00Z NAEFS MEAN THROUGH DAY 4. WE THEN TAPER OFF THE OPERATIONAL ECMWF AS IT MOVES TOWARD THE DEEP END OF THE ENVELOPE...ESPECIALLY FOR THE DAY 7 TROUGH IN THE EASTERN PACIFIC. BY THE END OF THE PERIOD OUR BLEND BECAME 70/30 ECMWF ENSEMBLE MEAN/NAEFS MEAN. ...SENSIBLE WEATHER HIGHLIGHTS... A HEAVY PRECIPITATION EVENT WHICH STRADDLES DAYS 3/4 WILL PROGRESS FROM NORTH TO SOUTH THROUGH CALIFORNIA ON THU/FRI. PRECIPITABLE WATER IS FORECAST AT A RESPECTABLE...ALTHOUGH NOT TOO ANOMALOUS 1.00 TO NEAR 1.25 INCHES ALONG THE COAST WITHIN THE ATMOSPHERIC RIVER. INTENSE HEIGHT FALLS AND 35 TO 60 KNOT SSW FLOW IN THE 850-700 MB LAYER WILL...HOWEVER...BOOST PRECIPITATION AMOUNTS...INCLUDING ALONG THE MORE SOUTHWARD FACING SLOPES OF THE COASTAL RANGES IN SOUTHERN CALIFORNIA. THIS SETUP GIVES GOOD REASON TO LEAN TOWARD THE MODELS PRODUCING THE HEAVIEST PRECIPITATION. TIMING OF THE NEXT UPSTREAM TROUGH IS LESS CERTAIN...BUT OUR ECMWF MEAN/NAEFS CONSENSUS APPROACH WOULD BRING A SIMILAR ALTHOUGH PERHAPS LESS INTENSE EVENT ONTO THE WEST COAST ON DAY 7. BY NEXT SUN/MON THE SRN PLAINS AND VICINITY MAY SEE ENHANCED RAINFALL GIVEN THE NUMBER OF MODEL RUNS CLOSING OFF AN UPR LOW WHILE STRENGTHENING LOW LEVEL GULF INFLOW. AHEAD OF THE UPPER TROUGH...TEMPERATURES WILL BE FAR ABOVE AVERAGE...ESPECIALLY OVER THE ROCKIES INTO THE NORTHERN PLAINS WITH SOME PLUS 20-30F ANOMALIES AND DAILY RECORDS POSSIBLE. RECORDS MAY BE SOMEWHAT MORE LIKELY FOR WARMEST MINIMUMS RATHER THAN DAILY MAXIMUM TEMPS. BURKE