MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1209 PM EST THU JAN 12 2017 VALID JAN 12/1200 UTC THRU JAN 16/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION INCLUDING PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SHORTWAVES SWINGING THROUGH GREAT LAKES/SERN CANADA THROUGH FRI COLD FRONT TRACKING ACROSS NEW ENGLAND AND THE OHIO VALLEY THU/FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE THE MODELS SHOWED SIMILARLY WITH THIS SYSTEM. CLOSED LOW REACHING NORTHERN MEXICO BY EARLY SUN MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 75% 12Z GFS...25% 00Z ECMWF CONFIDENCE: AVERAGE REGARDING THE CLOSED LOW OFF OF THE SRN CA COAST ON FRI AND EVENTUALLY MOVING EAST ACROSS NRN MEXICO...THE NAM/GFS/UKMET/CMC HAVE BEEN TRENDING SLOWER OR ARE NEAR THEIR PREVIOUS 2 12/00Z CYCLES. THE ECMWF IS THE ONLY DETERMINISTIC MODEL TRENDING FASTER WITH THE CLOSED LOW INTO THE SRN PLAINS FOR SUN. ENSEMBLE SPAGHETTI HEIGHT TRENDS ARE INCONCLUSIVE...BUT THEY DO INDICATE A SLIGHT TREND IN THE SLOWER DIRECTION AND MORE CLUSTERING TOWARD THE MIDDLE. CURRENTLY...THE 00Z ECMWF IS THE FASTEST TO KICK THE CLOSED LOW OUT INTO THE PLAINS...WITH THE 00Z UKMET SLOWEST. STAYING CLOSER TO THE MIDDLE APPEARS BEST AT THIS TIME...PERHAPS NEAR OLDER RUNS OF THE ECMWF AND CURRENT 12Z GFS. THEREFORE...THE PRELIMINARY PREFERENCE IS FOR A 12Z GFS/00Z ECMWF BLEND BUT WITH MORE WEIGHT TOWARD THE 12Z GFS. REGARDING THE FRONT ACROSS THE PLAINS AND RIDGING ACROSS THE SOUTHEAST...ENSEMBLE SPAGHETTI PLOTS HAVE SHOWN A CLEAR TREND TO BE STRONGER AND SLIGHTLY FARTHER WEST WITH THE MID-LEVEL RIDGE CENTERED OVER THE GULF OF MEXICO AND FLORIDA ENDING 12Z/14. THE NAM APPEARS BETTER IN HANDLING THE LOW LEVEL SURGE OF COLD AIR CURRENTLY OCCURRING ACROSS WEST TEXAS EARLY IN THE PERIOD...BUT IS WEAKER WITH THE RIDGE ACROSS THE SOUTHEAST BY 00Z/15 ALONG WITH THE 12Z GFS. SO PERHAPS TRENDS WITH THE RIDGE MAY BEGIN TO GO BACK TOWARD WEAKER WITH THE NEXT CYCLE. BEYOND 00Z/15...THE ENSEMBLE MEANS SPLIT THE DIFFERENCE WITH THE STRENGTH OF THE RIDGE AND PLACEMENT OF THE FRONT ACROSS THE SRN PLAINS. THE NAM REMAINS THE MOST AGGRESSIVE WITH THE LEADING EDGE OF COLD AIR WITH THE 12Z GFS WEAKEST...SO A GENERAL MODEL COMPROMISE IS RECOMMENDED TO HANDLE UNCERTAINTY WITH THE BOUNDARY 3 DAYS OUT FROM TODAY. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO