MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 250 PM EDT MON SEP 12 2016 VALID SEP 12/1200 UTC THRU SEP 16/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...EVALUATION OF THE 12Z MODEL GUIDANCE AND FINAL PREFERENCES ...BAND OF VORTICITY MOVING FROM THE BAHAMAS TO THE EASTERN FL PENINSULA... PREFERENCE: BLEND OF THE 12Z GFS/ECMWF FORECAST CONFIDENCE: AVERAGE A BROAD CLUSTER OF SHOWERS AND THUNDERSTORMS ACROSS THE BAHAMAS WILL CONTINUE TO PROPAGATE WESTWARD...WITH THE MID-LEVEL CIRCULATION REACHING THE EAST-CENTRAL COAST OF FL BY EARLY TUESDAY MORNING. THE 12Z NAM STILL APPEARED TO STRUGGLE WITH THE INTENSITY AND TRACK WHILE THE 12Z ECMWF/GFS WERE LESS AGGRESSIVE WITH THE INTENSITY OF THE FEATURE COMPARED WITH THE 12Z RUNS OF THE CMC/UKMET...AND REMAINS OUR PREFERENCE AT THIS POINT. ...PERSISTENT TUTT CELL MEANDERING ABOUT THE WESTERN/CENTRAL GULF OF MX... PREFERENCE: A NON NAM MODEL COMPROMISE FORECAST CONFIDENCE: AVERAGE WATER VAPOR IMAGERY ACROSS THE WESTERN/CENTRAL GULF COAST INDICATED A SLOW-MOVING TUTT CELL MOVING EASTWARD ACROSS SOUTHWESTERN LA. THE GUIDANCE GRADUALLY EXPAND THE CIRCULATION AS IT DIPS SOUTH INTO THE MIDDLE OF THE GULF OF MX. ALL SOLUTIONS GRADUALLY WEAKEN THIS FEATURE TOWARD 14/00Z EXCEPT THE NAM WAS REMAINS ON THE DEEPER/SLOWER SIDE OF THE GUIDANCE. WE CONTINUE TO FAVOR A NON NAM MODEL COMPROMISE. ...LONGWAVE TROUGH TRANSLATING ALONG THE NORTHERN TIER OF THE COUNTRY THIS WEEK... ...ATTENDANT SURFACE COLD FRONT/WAVES... PREFERENCE: BLEND OF THE 12Z GFS/ECMWF FORECAST CONFIDENCE: AVERAGE A POSITIVELY-TILTED TROUGH INITIALLY OVER WESTERN/CENTRAL CANADA DOWN INTO THE UPPER INTERMOUNTAIN WEST WILL MOVE SWIFTLY TOWARD THE EAST. THIS UPPER TROUGH WILL SPLIT WITH THE WESTERN FRINGE OF THE SHORTWAVES SINKING DOWN TOWARD THE CENTRAL GREAT BASIN/SOUTHWESTERN STATES. MEANWHILE...THE REMAINING HEIGHT FALLS WILL PROPAGATE TOWARDS THE EAST WHILE BEING REINFORCED BY A HIGHER LATITUDE IMPULSE CROSSING THE NORTH-CENTRAL U.S.. THE GFS KEPT A FAIR DEGREE OF RUN TO RUN CONSISTENCY WITH RESPECT TO THE FORWARD SPEED OF PROPAGATION AS THE WAVE SCOOTS ACROSS THE GREAT LAKES AND EVENTUALLY APPROACHES NEW ENGLAND. THE 12/12Z ECMWF/GFS FORM THE STRONGEST ALLIANCE WITH THE ENSEMBLE MEANS AND REMAINS THE FAVORED SOLUTION AT THIS POINT. ...INITIAL IMPULSE KICKING OUT OF THE DESERT SOUTHWEST EARLY IN THE PERIOD... ...CLOSED LOW BARRELING THROUGH THE SOUTHWESTERN CONUS ON TUESDAY/WEDNESDAY... PREFERENCE: BLEND OF THE 12Z ECMWF/ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: AVERAGE INITIALLY...AN OPEN WAVE WILL TRACK FROM INTERIOR CA TOWARD SOUTHERN UT DURING THE NEXT 24 HOURS WITH ONLY MINOR DIFFERENCES NOTED. TO THE NORTH...EVOLVING SPLIT FLOW WILL CARRY A ROBUST POSITIVELY-TILTED TROUGH THROUGH THE CENTRAL GREAT BASIN AND DOWN INTO THE SOUTHWESTERN STATES AS A CLOSED LOW BY 13/12Z. RELEVANT MODELS HAVE BEEN RATHER STABLE IN THE INITIAL EVOLUTION LOOKING AT THE PAST 36 HOURS OF RUNS. THERE IS SOME SOLUTION SPREAD BY 14/12Z WITH ENSEMBLE MEMBERS SCATTERED ABOUT. BUT THE DETERMINISTIC/ENSEMBLE RUNS CLUSTER WELL OVER NORTHERN NV ON WEDNESDAY MORNING. MODEL DIFFERENCES DO INCREASE AS THE CLOSED LOW OPENS UP AND HEIGHT FALLS SPREAD EASTWARD TOWARD THE HIGH PLAINS. GIVEN A SLOW-MOVING CLOSED LOW IN THE FORECAST...WILL ERR ON THE WESTERN END HERE WHICH IS MORE ALONG THE LINES OF THE CURRENT ECMWF AND THE PREVIOUS ECMWF ENSEMBLE MEANS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BANN