MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 304 AM EDT SUN MAY 01 2016 VALID MAY 01/0000 UTC THRU MAY 04/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ============================================== 00Z MODEL EVALUATION AND PREFERENCES ============================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ============================================== ...FRONTAL ZONE AND SHORTWAVES EJECTING FROM THE SOUTHWEST AND PLAINS TOWARD THE EAST COAST... ...NORTHERN STREAM SHORTWAVE SETTLING INTO THE MEAN LONGWAVE TROUGH BASE OVER THE PLAINS/SOUTHEAST... PREFERENCE: 00Z ECMWF CONFIDENCE: BELOW AVERAGE THOUGH THERE ARE A NUMBER OF SHORTWAVES...THE FLOW OVER THE CENTRAL AND EASTERN U.S. IS MORE BROADLY CHARACTERIZED BY A STORM TRACK TAKING IMPULSES OUT OF THE SOUTHWEST AND THE PLAINS TOWARD THE EAST COAST. A MEAN LONGWAVE TROUGH AXIS REMAINS ESTABLISHED OVER THE CENTRAL U.S. THROUGH DAY 3...AS NORTHERN AND SOUTHERN STREAM WAVES CONVERGE DOWNSTREAM OF A NORTHERN ROCKIES RIDGE. THE FIRST NOTEWORTHY SHORTWAVE AND SURFACE LOW REFLECTION ARE HANDLED SIMILARLY BY MOST OF THE MODELS...TRACKING TOWARD THE MID ATLANTIC BY MONDAY AND THEN TOWARD THE COAST OF NEW ENGLAND MONDAY NIGHT. THE GFS/ECMWF/UKMET COULD BE USED WITH CONFIDENCE. THE NAM WAS DECENT IN THE UPPER LEVELS...BUT ITS SURFACE LOW TRACK IS SOUTH OF THE RATHER STEADY MODEL CONSENSUS. THE CANADIAN ALSO LAGS BEHIND THAT CONSENSUS ON DAY 3. BACK FARTHER WEST...THE MODEL TRENDS AND SPREAD PRESENT SOME CHALLENGES. IF VIEWED AT FACE VALUE...THE 00Z OPERATIONAL MODELS CLUSTER AROUND A UKMET/CANADIAN SOLUTION...WITH A 04/12Z TROUGH AXIS INTO GEORGIA AND NO TRAILING SHORTWAVE OVER THE LOWER MISSISSIPPI VALLEY. FOR THE UKMET THIS WAS A REMARKABLE CHANGE...AS THE 12Z RUN HAD SUPPORTED THE ECMWF AND PREVIOUS THINKING WHICH HELD ONTO ENERGY RELATED TO A SMALL BUT PRONOUNCED SHORTWAVE THAT WILL DROP OUT OF CANADA MONDAY MORNING AND MAY DIG INTO THE LOWER MISSISSIPPI VALLEY LATE TUESDAY. THE GFS HAS BEEN CONTINUALLY UNDERPLAYING THIS FEATURE...AS SPAGHETTI PLOTS REVEAL THE GFS TO BE AT ONE EXTREME. UNFORTUNATELY...THE RUN TO RUN CHANGES IN THE OTHER MODELS ALSO FAIL TO INSPIRE CONFIDENCE. GENERALLY...IN A STREAM PHASING SITUATION...AS THIS IS...DOWNSTREAM OF THE NORTHERN ROCKIES RIDGE...THE ECMWF TENDS TO DO A BETTER JOB OF MAINTAINING THE IDENTITY OF INDIVIDUAL FEATURES...WHEREAS THE GFS IS SO QUICK TO PHASE THE STREAMS. THE GEFS IS SOMEWHAT SUPPORTIVE OF THE ECMWF...OR AT LEAST IS SUPPORTIVE OF THE ECMWF ENSEMBLE MEAN...HOLDING MORE ENERGY BACK ACROSS THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY DAY 3. FOR THESE REASONS...WE WILL CONTINUE TO HEDGE TOWARD THE ECMWF...WHILE NOTING THAT THE 00Z ECMWF DID SHARE THE OVERALL MODEL TREND OF GETTING THE LEADING TROUGH AXIS CLOSER TO GEORGIA BY THE END OF THE SHORT RANGE. THEREFORE...OUR CHOICE OF THE ECMWF DOES PARTIALLY EMBRACE THE TRENDS...WHILE HEDGING TOWARD THE SYNOPTIC PATTERN AND CONTINUITY FROM PREVIOUS CYCLES. ...DEEP UPPER TROUGH APPROACHING THE WEST COAST ON TUES... PREFERENCE: BLEND OF THE OPERATIONAL MODELS CONFIDENCE: ABOVE AVERAGE THE MODELS AGREE IN DEVELOPING A FULL-LATITUDE TROUGH OVER THE EASTERN PACIFIC OCEAN...AND THIS WILL APPROACH THE WEST COAST ON TUESDAY. THE GUIDANCE IS IN RELATIVELY GOOD AGREEMENT AND HAS SHOWN SOME STABILITY FROM RUN TO RUN. THE MAIN ODDITY WAS THE 12Z UKMET WHICH DEPICTED A SHARP SHORTWAVE TROUGH AT THE BASE OF THE LARGER SCALE TROUGH BY LATE TUESDAY. THE 00Z BACKED OFF OF THIS IDEA ENOUGH THAT THE UKMET COULD BE LUMPED WITH THE OTHER MODELS...FORMING A STRONG CONSENSUS. ...DEEP GREAT LAKES TROUGH DEVELOPING MON/TUE... PREFERENCE: BLEND OF 00Z NAM/ECMWF/UKMET CONFIDENCE: ABOVE AVERAGE THE PATTERN TRENDS TOWARD A DEVELOPING OMEGA BLOCK THAT SPANS THE ENTIRE U.S. BY DAY 3 INTO THE MEDIUM RANGE PERIOD. THIS WILL INCLUDE A CLOSED LOW DIGGING IN AND FEEDING INTO THE BROAD MEAN WEAKNESS/TROUGH OVER THE GREAT LAKES AND EASTERN U.S. TUESDAY. MODELS ARE PRETTY AGREEABLE ON THE LARGE SCALE...THOUGH THE 00Z GFS WAS A BIT QUICK....AND THE 00Z CANADIAN DEPICTED THE SURFACE LOW DISPLACED SOUTH AND WEST OF CONSENSUS. THE 00Z NAM/ECMWF/UKMET ARE BEST SUPPORTED...ESPECIALLY AT SURFACE...BY THE ENSEMBLE SURFACE LOW PLOTS SEEN OVER MULTIPLE MODEL CYCLES. THE 00Z GFS TRENDED TOWARD THE CONSENSUS...AND COULD NEARLY BE INCLUDED IN OUR PREFERENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE