MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 247 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 PREFERENCES AND FORECAST 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 ITS WEAK SURFACE LOW OVER GREAT LAKES BECOMING NEGATIVELY TILTED AS IT MOVES INTO NEW ENGLAND WED NIGHT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-12Z NAM MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z RUNS OF THE ECMWF...CMC...AND UKMET REMAIN CONSISTENT WITH THEIR PREVIOUS SOLUTIONS AND IN GOOD AGREEMENT WITH THE 12Z GFS. THE 12Z NAM IS STILL THE OUTLIER...MAINTAINING A MORE DISTINCT CIRCULATION THROUGH WED AS THE SYSTEM STARTS MOVING NORTHEAST OUT OF NEW ENGLAND. THIS IS IN LINE WITH ITS TYPICAL BIAS...AND IT IS THE LEAST FAVORED SOLUTION. 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: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE 12Z SOLUTIONS OF THE ECMWF...CMC...AND UKMET HAVE ALL TRENDED TOWARD THE 12Z GFS AND NAM SOLUTIONS...MAINTAINING A MORE DISTINCT UPPER CIRCULATION WITH THIS SYSTEM AS IT MOVES ACROSS THE ROCKY MOUNTAINS AND INTO THE CENTRAL PLAINS LATE WED. THE 12Z NAM IS MOST PRONOUNCED IN THIS REGARD WITH THE MOST SOUTHERLY POSITION...WHICH IS NO SURPRISE...BUT IT DOES NOT LOOK UNREASONABLE. IN ADDITION THE 12Z MODELS ARE IN GOOD AGREEMENT THAT THE SYSTEM WILL WEAKEN AS IT MOVES INTO THE UPPER MIDWEST ON THU...AND THEY AGREE NICELY ON THE TIMING AS WELL. A BLEND OF THE 12Z SUITE OF MODELS SHOULD WORK WELL. ...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: ABOVE AVERAGE THE 12Z ECMWF...CMC...AND UKMET ARE IN FAIRLY CLOSE AGREEMENT WITH THE 12Z GFS...MOVING THE MAIN UPPER LOW SLOWLY NNE FROM THE WA OFFSHORE WATERS ON WED TO THE VANCOUVER ISLAND OFFSHORE WATERS ON THU AND THEN SHIFTING IT INLAND ACROSS WESTERN CANADA ON FRI. IN GENERAL THESE 12Z MODEL SOLUTIONS CONTINUE THE TRENDS THEY SHOWED IN THEIR PREVIOUS RUNS...TIGHTEN THE CLUSTER OF SOLUTIONS...AND STRENGTHEN CONFIDENCE IN THE FORECAST. THE 12Z NAM CONTINUES TO BE THE CLEAR OUTLIER AMONG MODEL GUIDANCE...WITH THE UPPER LOW FURTHER SOUTH ALONG THE OR COAST AT 12Z THU AND THEN SHEARING A PORTION OF IT NE ACROSS WA ON THU. A BLEND OF THE 12Z MODEL SUITE THAT EXCLUDES THE 12Z NAM LOOKS LIKE A GOOD FORECAST WITH ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... MCDONNAL/ORRISON