MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 134 AM EST MON JAN 18 2016 VALID JAN 18/0000 UTC THRU JAN 21/1200 UTC ..SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION INCLUDING THE UKMET/CANADIAN/ECMWF AND PREFERENCES LOW PRESSURE ENTERING THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TUE... PREFERENCE: CLOSE TO THE GFS...EXCEPT SLIGHTLY SLOWER AND SOUTH CONFIDENCE: AVERAGE THE SPREAD REMAINS HIGH WITH THE PRECISE TIMING AND TRAJECTORY...WITH THE NAM AND ECMWF NEAR THE FAST AND SLOW EDGES OF THE GUIDANCE RESPECTIVELY...WITH THE ECMWF TRENDING FASTER THE LAST SEVERAL RUNS THAT WOULD SUPPORT THAT IT IS LAGGING BEHIND OTHER GUIDANCE. MEANWHILE...THE GFS IS CLOSE TO THE CONSENSUS UNTIL THE LOW REACHES THE OREGON COAST BY WHICH TIME IT BEGINS TO ACCELERATE PERHAPS IN RESPONSE TO UPSTREAM DIGGING OF ANOTHER TROUGH WHICH LIES NEAR THE STRONG EDGES OF THE GUIDANCE. GIVEN ITS DISTANCE UPSTREAM FROM THE CONSENSUS...THE LOW'S FORECAST MAY BE TOO FAR NORTH AND/OR FAST CLOSE TO SHORE. THUS...RECOMMEND A SLIGHTLY SLOWER/SOUTHWARD POSITION THAT IS TOWARD THE CANADIAN. SHORTWAVE TROUGH CROSSING THE PLAINS/MIDWEST TUE-WED... PREFERENCE: ECMWF CONFIDENCE: AVERAGE THIS TROUGH IS COMPRISED OF 2 PARTS...WITH THE NAM NEAR THE SLOW AND STRONG EDGES OF THE GUIDANCE WITH THE NORTHERN STREAM...GFS TOO FAST AND POSSIBLY SHOWING A LITTLE PHASING OF BOTH STREAMS RESULTING IN A SOLUTION NEAR THE AMPLIFIED SIDE OF THE GUIDANCE...AND ECMWF WHICH IS NEAR THE MIDDLE WITH BOTH STREAMS. GIVEN THE SHORT WAVELENGTH OF THESE TROUGHS AND CONTINUED RUN-TO-RUN VARIABILITY...THE PREFERENCE IS TO REMAIN NEAR THE CONSENSUS WHICH IS BEST APPROXIMATED BY THE 00Z ECMWF AND ALSO THE 00Z CANADIAN. CONFIDENCE REMAINS AVERAGE AT BEST. LOW PRESSURE FORMING OVER THE SOUTHERN PLAINS WED NGT... PREFERENCE: 1/4 EACH GFS/ECMWF/GEFS MEAN/ECMWF ENSEMBLE MEAN CONFIDENCE: LOW THE NEW ECMWF HAS TRENDED SLIGHTLY FASTER AND ALIGNS WELL WITH MOST DETERMINISTIC GUIDANCE EXCEPT THE GFS WHICH IS NEAR THE SLOW AND STRONG EDGES OF THE GUIDANCE...WHILE THE ENSEMBLE MEMBER SPREAD IS MUCH LARGER THAN THE DETERMINISTIC SPREAD. MEANWHILE...THE NAM IS THE SLOWEST ALOFT AND SO MAY BE DEEPENING THE LOW TOO SLOWLY. DESPITE ITS SLOWER/DEEPER SOLUTION AT THE SURFACE...A PREFERRED ASPECT OF THE GFS IS THAT MOST MODELS HAVE TRENDED TOWARD GREATER AMPLIFICATION...WHICH THE GFS REPRESENTS AND ALIGNS WELL WITH THE CONSENSUS ALOFT...AND SO IF BLENDED WITH SOME OF THE SLIGHTLY FASTER/WEAKER SOLUTIONS...AFFORDS A MIDDLE OF THE ROAD APPROACH. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... JAMES