MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 125 AM EST WED DEC 23 2015 VALID DEC 23/0000 UTC THRU DEC 26/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS INCLUDING THE UKMET/CANADIAN/ECMWF AND PREFERENCES LOW PRESSURE OVER THE S. PLAINS... PREFERENCE: NAM OR ECMWF CONFIDENCE: ABOVE AVERAGE THE NAM AND ECMWF ARE QUITE CLOSE TO THE EACH WHILE THE GFS HAS TRENDED TOWARD THEM BUT REMAINS TOO DEEP...ALTHOUGH ITS MOISTURE FIELDS ARE WELL ALIGNED WITH THE NAM/ECMWF. THE SPREAD HAS ALSO NARROWED WITH THE STRONGEST SUPPORT FROM OTHER GUIDANCE FOR THE NAM/ECMWF AS WELL. SHORTWAVE TROUGH OVER THE PAC NW... POSSIBLE LOW PRESSURE OVER THE C. PLAINS THU... PREFERENCE: ECMWF CONFIDENCE: AVERAGE WHILE INITIALLY QUITE SIMILAR...THE MODELS DIVERGE QUICKLY...WITH THE NAM MOVING TOWARD THE DEEP EDGE OF THE GUIDANCE...THE GFS TOWARD THE FAST EDGE...AND ECMWF REMAINING NEAR THE MIDDLE. GIVEN THE SPREAD AND HAVING LESS CONFIDENCE IN THE MORE EXTREME SOLUTIONS...RECOMMEND THE ECMWF. FRONTAL BOUNDARY DRAPED FROM THE LWR MS VALLEY TO MID-ATLANTIC THU-FRI... PREFERENCE: EQUAL BLEND NAM/GEFS MEAN/ECMWF ENSEMBLE MEAN CONFIDENCE: BELOW AVERAGE VERY HIGH SPREAD REMAINS WITH THE LINGERING FRONTAL BOUNDARY OVER THE MID-ATLANTIC AND ITS REDEVELOPING SOUTHWESTWARD INTO THE TN/MS VALLEYS FROM FRIDAY ONWARD. MID LEVEL FLOW COMPARISONS SHOW THE GFS TO HAVE THE GREATEST DISPLACEMENTS WITH THE PREFERRED CONFIGURATION OVER THE NORTHEAST AS WELL AS WITH THE UPPER LOW OVER THE WEST. THUS...RECOMMEND DISCOUNTING THE GFS. THE ECWMF GENERALLY LIES NEAR THE NORTHERN AND/OR WESTERN EDGES OF THE GUIDANCE...BUT HAS THE BEST SUPPORT ALOFT...WHILE THE NAM IS NEAR THE CONSENSUS FOR THE FRONT...BUT IS SLIGHTLY LESS PREFERRED ALOFT. GIVEN THESE PARTICULARS ALONG WITH THE SPREAD...RECOMMEND THE NAM OVERALL...ALTHOUGH ALSO RECOMMEND BLENDING IT WITH THE GEFS MEAN AND ECMWF ENSEMBLE MEAN WHICH ARE CLOSE TO THE NAM AND CAPTURE SOME OF THE NORTHERN AND SOUTHERN SIDES OF THE SOLUTION ENVELOPE AND HELP TO ADDRESS SOME CONCERNS WITH THE NAM ALOFT. UPPER TROUGH EVOLVING OVER THE GREAT BASIN/S. ROCKIES THU-FRI... PREFERENCE: EQUAL BLEND ECMWF AND ECMWF ENSEMBLE MEAN CONFIDENCE: AVERAGE THE GFS AS HAS BEEN THE CASE PERIODICALLY FOR SEVERAL DAYS REMAINS ON THE PROGRESSIVE SIDE OF THE GUIDANCE WITH EJECTING A LARGE PORTION OF THE LOW ACROSS WYOMING ON FRIDAY...WHICH IS A VERY DIFFERENT AND WEAKLY SUPPORTED TRAJECTORY COMPARED WITH OTHER GUIDANCE. THE ECMWF IS NEAR THE CONSENSUS AND IS RELATIVELY CLOSE TO THE NAM...ALTHOUGH THE NAM IS MORE DISTANT FROM THE CONSENSUS WITH ITS CLOSED NATURE TOWARD THE SOUTHWEST...THUS PREVENTING AS MUCH INVERTED TROUGHING AND MOISTURE TO DEVELOP OR ADVECT INTO THE CENTRAL AND NORTHERN PLAINS. THE SPREAD REMAINS MODEST AND THE PATTERN IS TRANSITIONING...THUS SOME CAUTION IS RECOMMEND TOWARD USING 1 PARTICULAR SOLUTION...WITH A BLEND OF SEVERAL SOLUTIONS PREFERRED INSTEAD. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... JAMES