MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 138 AM EST TUE DEC 22 2015 VALID DEC 22/0000 UTC THRU DEC 25/1200 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 CROSSING THE N. PLAINS TODAY/TONIGHT... PREFERENCE: GFS EXCEPT WEAKER CONFIDENCE: AVERAGE THE GFS LIES NEAR THE MODEL CONSENSUS FOR POSITION EXCEPT IS NEAR THE DEEP EDGE OF THE GUIDANCE DUE TO PHASING WITH THE NORTHERN STREAM...WHILE THE NAM IS SLOWER AND ECMWF SLIGHTLY FASTER...ALTHOUGH THE ECMWF'S 500 MB DEPICTION AND MOISTURE FIELDS ARE CLOSE TO THE GFS. GIVEN THE SLIGHT RUN-TO-RUN INCONSISTENCIES WITH MODEL DEPICTIONS OF THE SYSTEM...SOME UNCERTAINTY CONTINUES AND THEREFORE A CONSENSUS FOR POSITION IS RECOMMENDED. SHORTWAVE TROUGH OVER THE MS VALLEY... LOW PRESSURE FORMING ALONG THE NORTHEAST COAST TONIGHT... MODEL HAVE COME INTO GOOD LARGE-SCALE AGREEMENT. LOW PRESSURE CROSSING THE PLAINS/MIDWEST WED... COLD FRONT LINGERING OVER THE TN AND LOWER MS VALLEY THU... PREFERENCE: CONSENSUS WITH THE LOW AND NAM/GFS WITH THE LINGERING FRONT CONFIDENCE: BELOW AVERAGE THE FAST FLOW AND SHORT WAVELENGTHS OF INDIVIDUAL TROUGHS AND RIDGES ALONG WITH POSSIBLE INTERACTIONS OF MULTIPLE STREAMS ARE CONTRIBUTING TO CONTINUED SPREAD AND UNCERTAINTY. THE NAM AND GFS ARE FASTER AND STRONGER WITH THE LOW THAN THE ECMWF LARGELY DUE TO DIFFERENCES ALOFT...WITH THE ENSEMBLE MEANS AND ASSOCIATED ENSEMBLE MEMBER SPREAD SUPPORTING A CONSENSUS APPROACH TO ADDRESS THE UNCERTAINTY. REGARDING THE LINGERING FRONTAL BOUNDARY ACROSS THE SOUTH...THE NAM/GFS HAVE GOOD SUPPORT FROM THE GEFS MEAN AND 12Z ECMWF ENSEMBLE AS WELL AS THE UKMET/CANADIAN...WITH THE ECMWF NEAR THE NORTHWEST SIDE OF THE GUIDANCE BY 12Z FRI...AND THEREFORE CONSIDERED LESS PROBABLE. UPPER LOW FORMING OVER THE GREAT BASIN THU... PREFERENCE: 60 PERCENT GFS TO 20 PERCENT EACH 18Z GEFS MEAN/12Z ECMWF ENSEMBLE MEAN CONFIDENCE: AVERAGE DAY 3 IS A TRANSITIONAL PERIOD WITH SPLITTING OF THE FLOW OVER THE WEST AND DEVELOPMENT OF THE CLOSED LOW...WITH TRANSITIONS OFTEN BEST HANDLED WITH A MIXTURE OF THE MOST CURRENT GUIDANCE AND ENSEMBLES. THE GFS IS NEWEST...CLOSEST TO THE CONSENSUS...AND CAPTURES THE RECENT TREND OF SLIGHTLY SLOWER AND DEEPER...VERSUS THE SLOWER NAM AND QUICKER ECMWF. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... JAMES