MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 244 PM EDT SUN APR 30 2017 VALID APR 30/1200 UTC THRU MAY 04/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL ANALYSIS WITH PREFERENCES AND CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...CLOSED LOW CROSSING THE PLAINS ON SUNDAY AND UPPER MISSISSIPPI VALLEY ON MONDAY/TRAILING FRONT CROSSING THE ATLANTIC COAST MON NIGHT... PREFERENCE: NON-NAM BLEND OF 12Z MODELS CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z GLOBAL ECMWF...CMC...AND UKMET ARE CLOSE TO THE STRONG MODEL CONSENSUS SEEN IN THEIR 00Z RUNS AND THE 12Z GFS...SHOWING A WELL DEFINED CLUSTER OF SOLUTIONS AS THE CYCLONE MOVES NORTHEAST FROM THE PLAINS INTO THE UPPER MS VALLEY ON MONDAY. THE 12Z NAM IS CLOSE TO THIS SOLUTION AS WELL...HOWEVER IT SHOWS LESS PRECIPITATION WITHIN THE FRONTAL BAND AS IT MOVES ACROSS THE OHIO VALLEY AND THE GREAT LAKES REGION MON AND MON NIGHT. THE 12Z NAM FALLS SLIGHTLY BEHIND THE OTHER SOLUTIONS WITH THE PROGRESSION OF THE UPPER LOW TUE INTO WED AS IT MOVES FROM THE GREAT LAKES ACROSS NEW ENGLAND...SHOWING ITS TYPICAL TENDENCY TO MAINTAIN A TIGHTER UPPER CIRCULATION CENTER. THIS IS A FAIRLY MINOR DISCREPANCY AS THE SYSTEM IS EXITING THE UNITED STATES...BUT A BLEND OF THE 12Z MODELS EXCLUDING THE NAM LOOKS BEST. ...PACIFIC FRONTAL SYSTEM CROSSING THE SOUTHERN CANADIAN ROCKIES...WITH 700 MB TOUGH/SURFACE REFLECTION THAT MOVES OUT OF ALBERTA/SASKATCHEWAN ACROSS NORTHERN PLAINS/UPPER MISSISSIPPI VALLEY MON/TUE... PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z NAM MOVED CLOSE TO THE GENERAL MODEL CONSENSUS. IN ADDITION THE REMAINDER OF THE 12Z MODELS REMAINED CONSISTENT WITH THEIR PREVIOUS SOLUTIONS. ASIDE FROM FINE DETAILS...THE 12Z SUITE OF MODELS AGREE WELL WITH REGARD TO THIS FEATURE THROUGH TUE. A GENERAL BLEND OF THE 12Z MODELS SHOULD WORK WELL. ...WEAK PACIFIC WAVE ENTERING PACIFIC NORTHWEST LATE MON...CROSSING NORTH ROCKIES TUE...AND DIGGING INTO THE CENTRAL/SOUTHERN PLAINS TUE NIGHT/WED... PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: AVERAGE A WEAK SHORTWAVE TOPS THE MEAN RIDGE IN THE EASTERN PACIFIC AND MOVES SOUTHEAST ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES MON THROUGH TUE...THEN PROGRESSES INTO THE CENTRAL AND SOUTHERN PLAINS TUE NIGHT/WED. THERE IS STILL A DECENT AMOUNT OF SPREAD IN THE 12Z SUITE OF MODELS BY TUE NIGHT AND WED AS THE PATTERN AMPLIFIES AND THE SYSTEM DEVELOPS. THE 12Z GFS...12Z UKMET...AND 12Z ECMWF SPLIT THE VORTICITY MAXIMA BETWEEN THE MAIN UPPER TROUGH CENTERED OVER THE SOUTHERN PLAINS AND A TRAILING SHORTWAVE FURTHER NORTH-NORTHWEST OVER THE NORTHERN PLAINS. THE 12Z NAM IS RATHER ALONE NOW IN SHOWING MORE CONCENTRATED ENERGY IN THE MAIN TROUGH. THE 12Z CMC IS SOMETHING OF COMPROMISE BETWEEN THESE TWO GROUPS. THE DIFFERENCES SHOWN IN THE MASS FIELDS OF VARIOUS MODEL SOLUTIONS WILL MANIFEST THEMSELVES MOST IMPORTANTLY IN FRONTAL DEVELOPMENT AND QPF FIELDS TUE NIGHT/WED. THEY DIFFER WITH RESPECT TO WHERE THE HEAVIEST PRECIPITATION WILL OCCUR AND HOW MUCH THERE WILL BE. AT THIS POINT A COMPROMISE OF THE 12Z MODELS IS PROBABLY THE BEST WAY TO GO...BUT THE MODEL SPREAD YIELDS ONLY AVERAGE CONFIDENCE IN THE FORECAST. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ MCDONNAL