MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 249 PM EDT FRI APR 08 2016 VALID APR 08/1200 UTC THRU APR 12/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ UPPER TROUGH TRACKING FROM SWRN CANADA TO THE GREAT LAKES BY MON SURFACE LOW/FRONT CROSSING THE NORTHERN PLAINS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z UKMET AND 12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z NAM IS SLIGHTLY NORTH REGARDING THE TIMING/PLACEMENT OF THE SURFACE LOW RELATED TO THIS SYSTEM SUN MORNING AND THE 12Z GFS IS TOWARD THE FASTER SIDE OF THE MODEL SPREAD AND DEEPER SIDE IN THE MID-LEVELS. THE ENSEMBLE MEANS AND REMAINING DETERMINISTIC GUIDANCE SUPPORT A PLACEMENT TOWARD THE MIDDLE...CLOSER TO THE 12Z ECMWF/UKMET. INITIAL UPPER LOW LIFTING THROUGH THE SOUTHWEST FRI DEEP CLOSED LOW MOVING INTO SOUTHERN CA SAT NIGHT ENERGY SHEARING ACROSS THE SOUTHERN ROCKIES BY MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF 12Z GFS/ECMWF/CMC CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MOST SIGNIFICANT DIFFERENCE IN THIS AREA OF THE COUNTRY HAS TO DO WITH THE CLOSED LOW TO MOVE ACROSS THE WEST COAST SAT NIGHT. WHILE DECENT AGREEMENT EXISTS THROUGH SUN MORNING...THE NAM BECOMES A FASTER OUTLIER BY SUN EVENING ACROSS THE SOUTHWEST REGARDING THE WEAKENING UPPER TROUGH AS ENSEMBLES AND DETERMINISTIC GUIDANCE HAS TRENDED SLOWER. BY MON MORNING...THE FEATURE BEGINS TO SHEAR INTO CONFLUENT FLOW BUT THE 12Z UKMET REMAINS TOWARD THE FLATTER SIDE OF THE LATEST GUIDANCE WITH THE FEATURE. THE REMAINING 12Z GFS/ECMWF/CMC REPRESENT A GOOD COMPROMISE WITH SOME QUICKER ADJUSTMENTS MADE BY THE 12Z ECMWF VERSUS THE PREVIOUS RUN. NEXT UPPER LOW APPROACHING SOUTHERN CA BY MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: SLIGHTLY BELOW AVERAGE THE ENSEMBLES SHOW A WIDE RANGE OF TIMING/PLACEMENT DIFFERENCES BY MON MORNING ACROSS THE SOUTHWEST WITH THE CLOSED LOW...AND WHILE THE AMPLIFIED NATURE OF THE FLOW AND RECENT HISTORY SUGGESTS SLOWER IS BETTER HERE...THERE IS DECENT AGREEMENT AMONG THE 12Z MODELS WITH THE 12Z GFS A BIT FASTER...HOWEVER WITHIN THE SPREAD. WEAK SHORTWAVE TROUGH APPROACHING THE PACIFIC NORTHWEST BY MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 12Z GFS COMPROMISE CONFIDENCE: AVERAGE ALL OF THE MODELS SHOW A SHORTWAVE TROUGH APPROACHING THE PACIFIC NORTHWEST BY EARLY MON. THE 12Z GFS IS THE MOST AGGRESSIVE SOLUTION AT THIS POINT IN TAKING THE VORT ENERGY FARTHER SOUTH ALONG THE WEST COAST. THE REMAINING MODELS SHOW REASONABLE AGREEMENT AND ARE WITHIN THE ENSEMBLE SPREAD. SHORTWAVE/SURFACE LOW CROSSING THE NRN MID-ATLANTIC REGION SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS...12Z ECMWF...12Z CMC BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z NAM IS DISPLACED WEST OF THE REMAINING DETERMINISTIC CONSENSUS REGARDING THE CLOSED LOW-MID LEVEL LOW BY SAT MORNING OFF OF THE NRN MID-ATLANTIC COAST. THE NAM/GFS HAVE BEEN RATHER CONSISTENT OF THEIR PAST FEW RUNS...AND THE TODAYS 12Z ECMWF/UKMET/CMC HAVE SHOWN MINOR ADJUSTMENTS TOWARD THE 12Z GFS...BUT THE UKMET REMAINS TOWARD THE SOUTH SIDE OF THE GUIDANCE ON SATURDAY. CURRENTLY...A BLEND OF THE 12Z GFS/ECMWF/CMC APPEARS BEST GIVEN TRENDS AND ENSEMBLES REGARDING PLACEMENT AND STRENGTH OF THE UPPER/LOWER LEVEL LOW. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO