MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1255 AM EDT SAT JUN 18 2016 VALID JUN 18/0000 UTC THRU JUN 21/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...SURFACE FRONT ACROSS THE NORTHERN PLAINS/UPPER MIDWEST THROUGH SAT... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE A FRONT OVER THE NORTHERN PLAINS AND UPPER MIDWEST WILL STALL OUT AND TRANSITION INTO A WARM FRONT ON SAT OUT AHEAD OF ENERGY AND A SURFACE LOW EJECTING TOWARD THE NORTHERN HIGH PLAINS. DIFFERENCES WITH THE FRONTAL PLACEMENT ARE RELATIVELY SMALL...ALTHOUGH THE 12Z UKMET LOOKED LIKE IT WAS MAYBE DISPLACING THE BOUNDARY A LITTLE TOO FAR SOUTH. WILL MAINTAIN CONTINUITY FOR NOW AND CONTINUE WITH A GFS/ECMWF BLEND. ...UPPER-LEVEL LOW OVER THE PACIFIC NORTHWEST THROUGH SAT... ...ENERGY/SURFACE LOW EJECTING ACROSS THE NORTHERN PLAINS ON SUN... ...ATTENDANT COLD FRONT ADVANCING TOWARD THE GREAT LAKES ON MON... PREFERENCE: BLEND OF THE 00Z GFS/12Z ECMWF AND 12Z ECENS MEAN CONFIDENCE: SLIGHTLY BELOW AVERAGE THE GUIDANCE IS IN GOOD AGREEMENT WITH RESPECT TO THE UPPER-LEVEL LOW THAT CROSSES THE PACIFIC NORTHWEST THROUGH SAT. AFTER THAT TIME THE LOW COMES UNDER THE INFLUENCE OF STRONGER WESTERLIES AND BEGINS TO MOVE EASTWARD AND OPENS INTO A PROGRESSIVE SHORTWAVE THAT WILL TRAVERSE THE U.S./CANADIAN BORDER THROUGH SUN. DIFFERENCES EMERGE AMONG THE MODELS WITH RESPECT TO HOW QUICKLY THE SYSTEM OPENS INTO A WAVE AND MOVES EAST WHICH RESULTS IN DIFFERENCES WITH THE EVOLUTION OF A SURFACE LOW AND ATTENDANT COLD FRONT THAT CROSSES THE NORTHERN PLAINS/UPPER MS VALLEY AND GREAT LAKES THROUGH SUN AND MON. THE 00Z NAM/00Z GFS AND 12Z UKMET ALL GRADUALLY BECOME A LITTLE MORE PROGRESSIVE THAN THE 12Z CMC AND 12Z ECMWF THROUGH THE PERIOD AS THE LOW/COLD FRONT CROSSES THE NORTHERN PLAINS. AS THE COLD FRONT MOVES INTO THE GREAT LAKES REGION ON MON...THE TIMING SPREAD IS NOT PARTICULARLY SIGNIFICANT ALTHOUGH THERE IS MORE SUBSTANTIAL DISAGREEMENT WITH THE EXITING LOW CENTER LIFTING INTO CANADA SOUTH AND THEN EAST OF HUDSON BAY. OVERALL...THE 00Z GFS AND 12Z ECMWF AS A CONSENSUS APPEARS TO MAKE A REASONABLE COMPROMISE FOR FRONTAL TIMING AND THE SURFACE LOW DETAILS. THE 12Z ECENS MEAN TENDS TO FAVOR THIS CONSENSUS AS THE 18Z GEFS MEAN IS A BIT MORE OUT OF TOLERANCE. ...UPPER-LEVEL LOW OFF THE WEST COAST BY SUN/MON... PREFERENCE: GENERAL MODEL COMPROMISE...THROUGH SUN NON-NCEP MODEL CONSENSUS...MON AND TUES CONFIDENCE: AVERAGE A SECOND UPPER-LEVEL LOW IS FORECAST TO DEVELOP OFF THE WEST COAST BY SUN INTO MON. ONLY MINOR MASS FIELD DIFFERENCES ARE NOTED THROUGH SUN...BUT SPREAD INCREASES A BIT ON MON AND ESPECIALLY BY EARLY TUES AS THE UPPER LOW BEGINS TO OPEN UP INTO A TROUGH AXIS THAT ENCROACHES ON THE PACIFIC NORTHWEST. BY LATE MON AND TUES...THE 00Z NAM AND 00Z GFS ARE QUICKER TO BRING THE HEIGHT FALLS TOWARD THE PACIFIC NORTHWEST. THE 12Z UKMET/12Z CMC AND 12Z ECMWF ARE ALL A TAD SLOWER. THE 18Z GEFS MEAN AND 12Z ECENS MEAN BOTH FAVOR THE NON-NCEP SOLUTIONS IN BEING A LITTLE SLOWER. THUS...WILL PREFER A BLEND OF THE NON-NCEP SOLUTIONS BY MON AND TUES...WITH A GENERAL MODEL COMPROMISE PRIOR TO THIS. ...LOW DEVELOPING OFF THE EAST COAST BY SUN... PREFERENCE: BLEND OF THE 00Z NAM/00Z GFS AND 12Z UKMET CONFIDENCE: BELOW AVERAGE A CUTOFF UPPER-LEVEL LOW IS FORECAST TO EVOLVE FROM AN AMPLIFYING TROUGH OFF THE EAST COAST ON SUN AND MON AND RETROGRADE SOMEWHAT BACK TOWARD THE COAST ALONG WITH ITS ASSOCIATED SURFACE LOW. THE 12Z CMC IS AN OUTLIER SOLUTION IN KEEPING A STRONGER AREA OF LOW PRESSURE OFFSHORE THAT IS ALSO TUCKED IN CLOSER TO THE EAST COAST. THE 00Z NAM/00Z GFS/12Z UKMET AND 12Z ECMWF ARE ALL A BIT WEAKER AND FARTHER OUT TO SEA. HOWEVER...GRADUALLY THE ECMWF APPEARS TO BE TOO QUICK TO LIFT ITS LOW CENTER OFF TO THE NORTHEAST AND OUT TO SEA. THE NAM/GFS AND UKMET ACTUALLY ALL HAVE VERY GOOD CLUSTERING/AGREEMENT WITH THE TIMING/DEPTH OF THE LOW CENTER AS IT GRADUALLY LIFTS NORTHEAST AND AWAY FROM THE EAST COAST. THE 12Z ECENS MEAN DOES FAVOR THIS CONSENSUS...AND AS SUCH...A BLEND OF THE NAM/GFS AND UKMET WILL BE PREFERRED. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON