MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 254 AM EDT SUN APR 30 2017 VALID APR 30/0000 UTC THRU MAY 03/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL ANALYSIS AND PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...CLOSED LOW CROSSING THE PLAINS ON SUNDAY AND UPPER MISSISSIPPI VALLEY ON MONDAY/TRAILING FRONT CROSS THE EASTERN STATES TUE.... PREFERENCE: BLEND OF 00Z GFS/12Z-00Z ECMWF/00Z GEFS MEAN CONFIDENCE: AVERAGE THE ECMWF MEAN/GFS/ECMWF/UKMET ARE FORMING AN INCREASINGLY BETTER DEFINED CLUSTER OF SOLUTIONS WITH THE EVOLUTION OF THE CYCLONE MOVING NORTHEAST OUT OF THE PLAINS TOWARDS THE UPPER MS VALLEY. THE 00Z NAM IS STILL A FEW HOURS SLOW ON DAY 1 BUT PROGRESSES FASTER ON DAY 2 TO JOIN THE MAJORITY CLUSTER ACROSS THE UPPER MS VALLEY AND UPPER GREAT LAKES. THE 00Z NAM FALLS BEHIND AGAIN ON DAY 3/TUE AS IT LINGERS LOWER HEIGHTS/PRESSURE ACROSS THE GREAT LAKES VS THE OTHER MODELS. THE NAM SHOWS A BETTER DEFINED WAVE ALONG A BOUNDARY CROSSING NY STATE...WHICH WAS MORE AMPLIFIED THAN THE GFS/ECMWF/UKMET...SO CONFIDENCE IS LOW IN THE NAM. THE TRAILING COLD FRONT CROSSES THE NORTHEAST/MID ATLANTIC/SOUTHEAST STATES EARLY ON TUE. THE ECMWF HAS AMPLIFIED THE TROUGH WITH THIS BNDRY AND THERE IS NOW BETTER AGREEMENT WITH THE GFS/UKMET/SREF MEAN. WITH AN INCREASE IN CLUSTERING...A CONSENSUS OF THE 00Z GFS/12Z UKMET/21Z SREF MEAN/00Z ECMWF IS RECOMMENDED. ...PACIFIC FRONTAL SYSTEM TRANSLATING ACROSS THE S CANADIAN ROCKIES...WITH 700 MB TOUGH/SFC REFLECTION THAT MOVES OUT OF ALB/SASK ACROSS NORTHERN PLAINS/UPPER MS VALLEY MON/TUES... PREFERENCE: 00Z GFS...00Z ECMWF...00Z UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 00Z NAM CONTINUES TO BE STRONGER THAN THE REMAINING DETERMINISTIC AND ENSEMBLE MODEL CONSENSUS ACROSS SWRN CANADA ON MON MORNING..WITH LOWER 700 MB HEIGHTS EXTENDING INTO NORTHEAST MT/NORTHERN ND VS THE GFS/ECMWF/UKMET AND RESPECTIVE ENSEMBLE MEANS. THIS WAVE DOES WEAKEN IN ALL THE MODELS LATER ON MON AND MON NIGHT WITH THE WEAKENING WAVE ROTATING UNDER THE BASE OF THE UPPER MS VALLEY TROUGH...AND THE NAM AGREES WITH THIS IDEA. BETTER AGREEMENT EXISTS FOR THE MIDDLE ROAD BEST REPRESENTED BY THE 18Z-00Z GFS/12Z-00Z ECMWF/00Z UKMET. ...WEAK PACIFIC WAVE ENTERING PACIFIC NORTHWEST LATE MON AND CROSSING N ROCKIES BY TUES MORNING... PREFERENCE: 18Z GEFS MEAN/00Z GFS/12Z ECMWF/00Z UKMET BLEND CONFIDENCE: AVERAGE A WEAK SHORTWAVE TOPS THE MEAN RIDGE IN THE EASTERN PACIFIC AND MOVES SOUTHEAST ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES MONDAY AND THEN INTO THE NORTHERN TO CENTRAL PLAINS AND CENTRAL ROCKIES TUE...DEVELOPING FURTHER SOUTH ACROSS THE PLAINS AND ROCKIES AS TUE PROGRESSES. THE 18Z GFS STOOD OUT BY DEVELOPING A HIGHER AMPLITUDE 700 MB WAVE CROSSING WY AND THEN INTO NE ON TUE...WITH THE GEFS MEAN AND NOW THE 00Z GFS SHOWING A LOWER AMPLITUDE SOLUTION..AND THE ECMWF EVEN LOWER AMPLITUDE THAN THE GEFS MEAN. THE 00Z UKMET BACKED OFF THE 12Z RUN IDEA OF DEVELOPING A SHARPER 700 MB WAVE IN SOUTHEAST WY THAT PROGRESSES ACROSS EASTERN CO...SO THE 00Z UKMET NOW AGREES BETTER WITH THE GFS/GEFS MEAN ACROSS CO. THE MODELS ARE IN FAVOR OF THE WAVE GRADUALLY AMPLIFYING AS IT CROSSES CO/CENTRAL PLAINS INTO NM AND THE SOUTHERN PLAINS. THE NAM STOOD OUT BY HAVING A FASTER 700 MB WAVE MOVING OUT OF THE PLAINS INTO THE LOWER MS VALLEY...WITH GOOD CLUSTERING AMONG THE 00Z GFS/00Z ECMWF AND THEIR ENSEMBLE MEANS...AS WELL AS THE 00Z UKMET. ONE DIFFERENCE IS THE UKMET DEVELOPS STRONGER SFC LOW PRESSURE 12Z WED COMPARED TO THE OTHER SOLUTIONS SO THE 00Z UKMET MIGHT BE A BIT TOO STRONG 12Z WED. THEREFORE A BLEND OF THE 00Z GEFS MEAN/12Z ECMWF/00Z GFS IS RECOMMENDED FOR THIS SYSTEM. ...PACIFIC CYCLONE OFFSHORE OF THE PACIFIC NORTHWEST MON-WEAKENING TUE... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 18Z GFS/00Z ECMWF/00Z UKMET BLEND CONFIDENCE: AVERAGE THE MODELS SHOW A WEAK CYCLONIC CIRCULATION MONDAY THAT WEAKENS INTO AN ELONGATED SHEAR AXIS/WARM FRONT ON TUE THAT APPROACHES VANCOUVER ISLAND. THE NAM/21Z SREF MEAN/0Z GFS BRING GREATER PRESSURE FALLS AND STRONG LOW LEVEL CONVERGENCE INTO WA STATE THAN THE 18Z GFS/12-00Z ECMWF/00Z UKMET...WHICH REBUILD A LOW LEVEL RIDGE AND WEAKEN THE TROUGH AS IT APPROACHES. RECENT TRENDS HAVE SHOWN MORE MID-LEVEL RIDGING AHEAD OF THE CLOSED LOW IN THE GULF OF AK. GIVEN THE 12Z-18Z GFS AND 12Z-00Z ECMWF AND 00Z UKMET ARE IN SYNCH WITH THE TRENDS...THEY REPRESENT THE PREFERENCE. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ PETERSEN