MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 122 AM EDT TUE AUG 18 2015 VALID AUG 18/0000 UTC THRU AUG 21/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION AND ANALYSIS INCLUDING PREFERENCES AND FORECAST CONFIDENCE DEEP UPPER TROUGH AFFECTING THE NORTHERN PLAINS/MIDWEST INTENSE SURFACE LOW LIFTING UP THROUGH THE UPPER GREAT LAKES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE *12Z/18Z GFS*/12Z ECMWF & 12Z/18Z GEFS MEANS CONFIDENCE: BELOW AVERAGE LARGE SHIFT SEEN WITH THE 00Z GFS AWAY (FASTER AND WEAKER) FROM STRONG CLUSTERING/SUPPORT OF RECENT 12Z AND 18Z RUNS ALONG WITH THE 12Z AND 18Z GEFS MEMBERS BEGS SOME QUESTIONS ON ITS RELIABILITY AND THOUGH IT HAS SHIFTED CLOSER TO THE 12Z ECMWF IT ALSO PASSED IT IN TIMING. RUN TO RUN COMPARISONS ACROSS WY/MT SUGGEST THE 00Z GFS MAY HAVE INITIALIZED A BIT BROADER WITH VORT CENTERS CIRCLING A WEAK CENTRAL HUB COMPARED TO EARLIER RUNS AND RAPID REFRESH ANALYSIS FROM THE RAP. THE 00Z NAM AND 12Z CMC ARE SLOWER COMPARED TO THE GFS/ECMWF BUT ALSO LAG SLOWER HAVING STRONGER UPSTREAM WAVES THAT KEEP THE OVERALL TROF MORE NEUTRAL TILT COMPARED TO THE 00Z GFS AND 12Z ECMWF. IN KEEPING WITH CONTINUITY WITH CONSISTENCY THIS FAVORS THE 12Z AND 18Z GEFS MEANS. ADDING THE *12Z/18Z* GFS AND 12Z ECMWF. GIVEN SPREAD ACROSS THIS PREFERENCE AND CHANGES SEEN UPSTREAM CONFIDENCE IS BELOW AVERAGE ACROSS THE PLAINS AND UPPER MIDWEST. FURTHER SOUTH/SOUTHERN PLAINS... THE TIMING OF THE FRONT TRAILING BACK TO THE LEE CYCLONE APPEAR TO BE IN STRONG AGREEMENT WITH THE INITIAL PREFERENCE (00Z NAM AT MUCH BETTER CONFIDENCE HERE. SHORTWAVE TROUGH DIGGING THROUGH BRITISH COLUMBIA BY THURS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF OPERATIONAL MODELS---- CONFIDENCE: AVERAGE MODELS SHOW SHORTWAVE ADVANCING OUT OF THE GULF OF ALASKA TO AFFECT TO DIG A MODERATE WESTERN TROF BY FRIDAY OUT OF BRITISH COLUMBIA. TIMING AND DEPTH SEEM TO BE IN FAIRLY GOOD AGREEMENT OF THE DETERMINISTIC MODELS GIVEN IT IS AT DAY 3 AND THERE REMAINS GOOD SPREAD SEEN IN THE 500 MB ENSEMBLE SPAGHETTI PLOTS. THE 12Z ECMWF IS MOST FORWARD LEANING FOLLOWED BY THE 12Z CMC AND 12Z UKMET...BUT ALSO LEADING THE 12Z ECMWF ENSEMBLE MEAN...THOUGH THE MAJORITY OF THE SPREAD IN THE ENSEMBLE SPAGHETTI APPEARED TO BE ECMWF MEMBERS WITH SOME CMC MEMBERS TOO. THE SLOWER 00Z GFS AND 00Z NAM WERE STILL WITHIN GOOD DISTANCE OF 12Z ECMWF TO NOT DISCOUNT ANY PARTICULAR MODEL...BUT WITH BETTER PACKING AND ORIENTATION COMPARED TO THE 21Z SREF/18Z GEFS AND 12Z ECMWF ENSEMBLE MEAN... PREFERENCE IS A BLEND OF THE OPERATIONAL MODELS WITH HIGHER WEIGHTING TOWARD THE 00Z GFS/NAM AT AVERAGE CONFIDENCE. MID LEVEL VORT CENTER LIFTING NORTH ACROSS THE LOWER OH VALLEY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A WELL-DEFINED MID LEVEL VORT CENTER LIFTING NORTH ACROSS CENTRAL OHIO ATTM IN WV SHOULD BEGIN TO SHEAR AS IT LIFTS NORTHEAST INTO MORE CONFLUENT FLOW BY LATE TUESDAY ACROSS NORTHERN NEW YORK. A BLEND OF THE OPERATIONAL MODELS IS PREFERRED...HOWEVER...GIVEN HOW CONSOLIDATED IT APPEARS TO BE INITIALIZED AND RETAINED IN THE 00Z GFS AND 12Z ECMWF/CMC... HIGHER WEIGHTING IS GIVEN TO THESE THREE OVER THE 00Z NAM/12Z UKMET TO RETAIN THE FEATURE BEST. WESTERN GULF COAST TROUGH/SHEAR AXIS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 00Z/NAM/GFS AND 12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE A WELL-DEFINED AND ELONGATED MID LEVEL SHEAR AXIS STRETCHING FROM THE LOWER MS VALLEY DOWN THROUGH THE WESTERN GULF COAST REGION IS EXPECTED TO RETROGRADE WEST-SOUTHWEST INTO CENTRAL AND SOUTHERN TX ON TUES BEFORE THEN STALLING OUT. THE 12Z UKMET REMAINS THE WEAKEST TO RESOLVE THIS WAVE AND THE 12Z CMC APPEARS TO FEEL THE INFLUENCE OF THE LIFTING TROF...PULLING/SHEARING THE WAVE EAST AND NORTH NOT IN LINE WITH OTHER SOLUTIONS. THE 00Z GFS AND NAM ARE IN QUITE GOOD AGREEMENT KEEPING THE LOW GENERALLY CONSOLIDATED AND STATIONARY OVER SOUTH TEXAS EVENTUALLY DEVELOPING WHAT APPEARS TO BE CONVECTIVE FEEDBACK...THOUGH GIVEN PLACEMENT/THERMODYNAMIC ENVIRONMENT...SOME CREDENCE MUST BE GIVEN FOR THE POTENTIAL FOR SOME CONVECTIVE SYSTEM TO EXIST. THE 12Z IS A BIT WEAKER AND LESS AGGRESSIVE BUT GIVEN PLACEMENT....A BLEND OF THE 00Z NAM/GFS AND 12Z ECMWF LOOKS GOOD HERE AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA