MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1245 PM EDT TUE APR 11 2017 VALID APR 11/1200 UTC THRU APR 15/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING INITIAL PREFERENCES AND CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...SHORTWAVE TROUGH MOVING FROM LOWER MISSISSIPPI VALLEY ACROSS GULF COAST STATES THROUGH WED... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE NO SIGNIFICANT DIFFERENCES IN MODELS AND A GENERAL MODEL BLEND IS RECOMMENDED. ...UPPER TROUGH AND WEAK SURFACE LOW OVER GREAT LAKES BECOMING NEGATIVELY TILTED AS IT MOVES INTO NEW ENGLAND WED NIGHT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE MODELS CONTINUE TO SHOW GOOD AGREEMENT AND RUN TO RUN CONSISTENCY...WITH ONLY MINOR DETAIL DIFFERENCES. SPECIFICALLY THE 12Z NAM MAINTAINS A MORE DISTINCT CIRCULATION THROUGH WED AS THE SYSTEM STARTS MOVING NORTHEAST OUT OF NEW ENGLAND...WHICH IS IN LINE WITH ITS TYPICAL TENDENCY. A GENERAL MODEL BLEND THAT EXCLUDES THE 12Z NAM IS RECOMMENDED TO IRON OUT SMALLER SCALE DIFFERENCES. ...MINOR UPPER SHORTWAVE MOVING INTO NRN CA/OR TODAY...PROGRESSING ACROSS CENTRAL PLAINS/UPPER MIDWEST ON WED AND THU... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-00Z ECMWF MODEL BLEND CONFIDENCE: AVERAGE THE 12Z NAM AND GFS SOLUTIONS MAINTAIN A MORE DISTINCT UPPER CIRCULATION WITH THIS SYSTEM AS IT MOVES ACROSS THE CENTRAL PLAINS ON WED AND...TO A LESSER DEGREE...AS IT MOVES ACROSS THE UPPER MIDWEST ON THU. AS MENTIONED IN THE PREVIOUS DISCUSSION...THE 00Z ECMWF APPEARS TOO PROGRESSIVE AND FLAT COMPARED TO THE CONSENSUS OF THE OTHER DETERMINISTIC AND ENSEMBLE GUIDANCE. THE 00Z UKMET AND CMC MODELS ARE ROUGHLY A COMPROMISE BETWEEN THE 12Z NAM AND GFS SOLUTIONS AND THE 00Z ECMWF. DESPITE THE DIFFERENCES DISCUSSED ABOVE...THESE ARE MAINLY DISCREPANCIES THAT WILL AFFECT THE FINER DETAILS OF THE FORECAST. A BLEND OF THE MODELS THAT PUTS MINIMAL WEIGHT ON THE 00Z ECMWF IS PROBABLY THE BEST SOLUTION. ...SURFACE LOW MOVING THROUGH PACNW TONIGHT/WED MORNING... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE NO SIGNIFICANT DIFFERENCES IN MODELS AND A GENERAL MODEL BLEND IS RECOMMENDED. DEEP CLOSED LOW APPROACHING WEST COAST LATE WED AND MOVING SLOWLY NORTH OVER PACNW OFFSHORE WATERS THROUGH FRI... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-12Z NAM MODEL BLEND CONFIDENCE: AVERAGE THE 12Z NAM IS THE OUTLIER AMONG MODEL GUIDANCE...WITH THE UPPER LOW FURTHER SOUTH ALONG THE OR COAST AT 12Z THU AND THEN MORE OR LESS DISSIPATING AS IT MOVES NORTHWEST ACROSS WA ON THU. THE 00Z NAM ALSO SHOWED THE LOW MOVING INLAND IN A SIMILAR FASHION. THE 00Z ECMWF...CMC...AND UKMET ARE IN A FAIRLY TIGHT CLUSTER WITH THE UPPER LOW MOVING NNE FROM OFFSHORE WA TO OFFSHORE VANCOUVER ISLAND ON THU. THE 12Z GFS IS SLIGHTLY FURTHER SOUTH THAN THIS CLUSTER BUT FOLLOWS THE SAME GENERAL IDEA WITH REGARD TO THE TRACK OF THE LOW...AND IT HAS TRENDED TOWARD THIS CLUSTER IN COMPARISON TO THE 00Z GFS. THIS IS ALSO THE IDEA OF THE 00Z GFS ENSEMBLE. LOW PRESSURE FURTHER NORTH OVER THE OFFSHORE WATERS OF NORTHERN BC AND SOUTH OF AK...AS WELL AS SYNOPTIC CLIMATOLOGY...FAVOR THESE SOLUTIONS OVER THE NAM. SO A BLEND OF MODELS THAT EXCLUDES THE NAM LOOKS BEST. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... MCDONNAL/ORRISON