MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1157 PM EST WED DEC 28 2016 VALID DEC 29/0000 UTC THRU JAN 01/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... ...STRONG UPPER TROUGH THE NORTHEASTERN U.S. LATE THURSDAY/EARLY FRIDAY... ...INTENSE COASTAL LOW DEVELOPING OFF OF NEW ENGLAND... PRELIMINARY PREFERENCE: NON-21Z SREF MEAN MODEL CONSENSUS FORECAST CONFIDENCE: ABOVE AVERAGE AMPLIFYING FLOW NOTED ON WATER VAPOR IMAGERY AND 500-MB HEIGHTS SHOWED A WELL-DEFINED UPPER TROUGH EXTENDING FROM ONTARIO DOWN THROUGH THE UPPER GREAT LAKES INTO THE MIDDLE MS VALLEY. THIS CORRIDOR OF STRONG HEIGHT FALLS WILL WORK THEIR WAY EASTWARD WHILE EVENTUALLY EVOLVING INTO A NEGATIVELY-TILTED TROUGH OVER THE UPPER MID-ATLANTIC COAST BY 30/0000Z. THIS ULTIMATELY AIDS IN THE DEVELOPMENT OF AN IMPRESSIVE COASTAL LOW WHICH MAY DEEPEN TO BELOW 970-MB BY 30/1200Z ACROSS NORTHERN MAINE. ENSEMBLE LOW PLOTS THE PAST COUPLE OF MODEL CYCLES HAVE SHOWN REMARKABLY STRONG AGREEMENT ACROSS THE BOARD. THE 21Z SREF MEAN DOES GET A BIT NORTH OF THE CONSENSUS BY FRIDAY ONWARD. CONSEQUENTLY...WILL RECOMMEND A NON-21Z SREF MEAN MODEL CONSENSUS. ...CUT-OFF LOW OVER THE SUBTROPICAL PACIFIC TRACKING THROUGH SOUTHERN CA BY 30/1800Z... PRELIMINARY PREFERENCE: 12Z ECMWF FORECAST CONFIDENCE: AVERAGE AN UPPER LOW WHICH HAS BEEN CUT-OFF FOR A WHILE NOW WILL FINALLY SHIFT ITS FOCUS BACK TOWARD THE SOUTHWESTERN U.S. BY FRIDAY. THIS SYSTEM SHOULD DEFINITELY PICK UP SOME FORWARD SPEED AS IT FEELS THE INFLUENCES OF A SHARPENING LONGWAVE TROUGH ACROSS THE PACIFIC NORTHWEST. THERE ARE SOME DIFFERENCES IN TIMING AS INDICATED BY THE 570-DM SPAGHETTI PLOTS AS THE ECMWF ENSEMBLE MEMBERS HAVE FAVORED A SLOWER EASTWARD PROGRESSION. ON THE OTHER SIDE OF THE SPECTRUM IS THE 21Z SREF MEAN WHICH SUGGESTS SOMETHING MORE DAMPENED WHICH SWINGS THE SYSTEM MORE QUICKLY TOWARD AZ/NM. OVERALL...PREFER THE SLOWER SIDE OF THE SPREAD GIVEN THE TENDENCY FOR MODELS TO BE TOO QUICK AT EJECTING CUT-OFF LOWS. THE 12Z ECMWF WOULD REPRESENT THIS SCENARIO QUITE WELL HERE. ...POSITIVELY-TILTED TROUGH SWEEPING THROUGH THE NORTHERN TIER STATES BY FRIDAY... ...ATTENDANT SURFACE CYCLONE/FRONTAL ZONE... PRELIMINARY PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE A STRONG LOBE OF VORTICITY CURRENTLY WELL WEST OF BRITISH COLUMBIA WILL ACCELERATE EASTWARD WHILE EVENTUALLY DRAGGING SHARP HEIGHT FALLS ACROSS THE ALBERTA/SASKATCHEWAN BORDER ON FRIDAY MORNING. MODELS ARE IN DECENT AGREEMENT WITH THE TIMING OF THE UPPER TROUGH BUT THERE ARE SOME DIFFERENCES IN THE DETAILS REGARDING THE LOW TRACK. THE 12Z CMC AND ITS ASSOCIATED ENSEMBLE MEMBERS ARE WELL TO THE SOUTH OF THE STRONG CLUSTERING. A MUCH MORE CONSOLIDATED SOLUTION IS EVIDENT BETWEEN THE 00Z GFS/12Z GFS-PARALLEL AS WELL AS THE 12Z ECMWF/UKMET AND THE ENSEMBLE MEANS. WILL FAVOR THE DUO OF THE 00Z GFS/12Z ECMWF GIVEN THE 12Z UKMET BECOMES SLOW BY DAY 3. ...CLOSED LOW BARRELING DOWN THE CA COAST THIS WEEKEND... PRELIMINARY PREFERENCE: A NON-12Z CMC MODEL CONSENSUS FORECAST CONFIDENCE: ABOVE AVERAGE WITHIN THE POSITIVELY-TILTED TROUGH SWINGING THROUGH WESTERN BRITISH COLUMBIA ON 30/0000Z...A SPLIT IN THE JETS IS NOTED AS THE SOUTHWESTERN EXTENT OF THIS FEATURE WILL QUICKLY SURGE SOUTHWARD...GENERALLY STRADDLING THE IMMEDIATE WEST COAST. THE 12Z GFS-PARALLEL DOES LAG THE CONSENSUS BUT ITS INITIALIZATION BEING 12 HOURS BEHIND MORE RECENT SOLUTIONS MAY HAVE SOMETHING TO DO WITH THAT. OVERALL...MODELS HAVE GENERALLY BECOME MORE STABLE COMPARED TO A FEW RUNS AGO WHICH WERE SLOWER WITH MUCH SCATTER AMONG THE ENSEMBLE MEMBERS. BY SATURDAY...THE 12Z CMC EXITS THE STRONGER CLUSTER BECOMING QUICKER WHILE MOVING THROUGH THE SOUTHERN CA DESERTS. GIVEN THE GOOD AGREEMENT WITH THE TRACK OF THIS COMPACT UPPER LOW...WOULD SUGGEST A MODEL CONSENSUS AMONG THE NON-12Z CMC SOLUTIONS. ...NEXT POWERFUL SYSTEM AFFECTING THE NORTHWESTERN U.S. LATE IN THE PERIOD... PRELIMINARY PREFERENCE: 12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: BELOW AVERAGE ON THE HEELS OF THE INITIAL CLOSED LOW MOVING DOWN THE WEST COAST INTO THE DESERT SOUTHWEST...A BROADER UPPER TROUGH WILL ENCOMPASS THE PACIFIC NORTHWEST LATER IN THE FORECAST. MODEL DIFFERENCES ARE MUCH LARGER WITH THIS SYSTEM WITH DETERMINISTIC/ENSEMBLE SOLUTIONS ALL AT ODDS WITH ONE ANOTHER. AFTER COLLABORATING WITH WPC MEDIUM RANGE...DECIDED TO MOVE TOWARD THE FASTER CAMP BRINGING IN THE COLD AIR MORE QUICKLY WHICH IS ALONG THE LINES OF THE 12Z ECMWF ENSEMBLE MEAN. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER