MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 153 PM EST SAT JAN 14 2017 VALID JAN 14/1200 UTC THRU JAN 18/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION INCLUDING FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ *CLOSED LOW REACHING THE SOUTHERN PLAINS BY MON MORNING SURFACE LOW TRACKING FROM THE SOUTHERN PLAINS TO THE UPPER MIDWEST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/GFS/ECMWF BLEND THROUGH 12Z/16 12Z ECMWF/00Z UKMET BLEND 12Z/16-00Z/18 CONFIDENCE: SLIGHTLY BELOW AVERAGE THE STRENGTH OF THE MID-LEVEL RIDGE ACROSS THE SERN U.S. AT 12Z TODAY WAS SLIGHTLY STRONGER THAN INDICATED BY THE MODELS. ACROSS NM/TX BY 00Z/16...TRENDS IN THE ENSEMBLE GUIDANCE HAVE BEEN TO WEAKEN THE EXPANSE OF THE 500 MB LOW OVER THE PAST 4 CYCLES...WITH THE 00Z ECMWF/ECMWF MEAN CURRENTLY THE LARGEST. THE 00Z ECMWF ALSO HAS THE WEAKEST MID-LEVEL RIDGING DOWNSTREAM ACROSS THE CNTRL PLAINS BY 00Z/16. GIVEN POSSIBLE WEAK INITIALIZATION/FORECASTS ACROSS THE SOUTHEAST AND THE 00Z ECMWF PRESENTLY ON THE WEAKER SIDE WITH RESPECT TO THE ENSEMBLES...IT IS NOT FAVORED ACROSS THE CNTRL U.S. THROUGH ABOUT 12Z/16 TO 00Z/17. THE TRACK OF THE 12Z NAM 500 MB LOW AND SURFACE LOW ENDS UP ON THE FAR WESTERN END OF THE ENSEMBLE GUIDANCE AFTER 12Z/16...BUT THE NAM SEEMS USABLE UP UNTIL 12Z/16. BEYOND 12Z/16...THE 12Z GFS ENDS UP FASTER THAN MOST GUIDANCE WITH THE TRACK OF THE 500 MB LOW ACROSS THE MIDWEST...WITH THE ENSEMBLE MEAN 500 MB AND SURFACE LOW TRACKS BEST AGREEABLE TO THE 00Z ECMWF/UKMET THROUGH 00Z/18. GIVEN THE COMPLEX INTERACTION OF THIS FEATURE WITH THE ONE DESCRIBED IN THE BELOW SECTION...CONFIDENCE IS A BIT BELOW AVERAGE. 19Z UPDATE...THE 12Z ECMWF FOLLOWED THE WEAKENING TREND WITH THE 500 MB LOW AND STRONGER DOWNSTREAM RIDGE WHICH INCREASES CONFIDENCE IN ITS SOLUTION. REGARDING THE SURFACE LOW AND COLD FRONT TRACKS...ENSEMBLES SUPPORT A BLEND OF THE 12Z ECMWF AND 00Z UKMET...WITH THE 12Z UKMET PERHAPS NOT TOO FAR OFF OF THIS PREFERENCE...BUT ITS DEPICTION OF A POSSIBLY TOO DEEP UPSTREAM TROUGH AXIS MAY PULL THE LOW TRACKING TOWARD THE GREAT LAKES TOO FAR WEST. SHORTWAVE CROSSING THE NRN ROCKIES/NRN PLAINS SUN NIGHT/MON INTERACTION WITH THE SHORTWAVE TRACKING FROM THE SRN PLAINS INTO THE MIDWEST MON/TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF/12Z UKMET BLEND CONFIDENCE: AVERAGE THE 12Z CMC AND 12Z NAM ARE ON THE DEEPER END OF THE ENSEMBLE GUIDANCE WITH THE BASE OF THE UPPER TROUGH AS IT REACHES THE CNTRL/NRN HIGH PLAINS MON. TRENDS HAVE BEEN WEAKER WITH THIS FEATURE IN THE ENSEMBLE GUIDANCE AND STRONGER IN THE 12Z ECMWF/UKMET/CMC...BUT A MODERATE SPREAD REMAINS WITH ALL OF THE DETERMINISTIC MODELS FALLING WITHIN THE REALM OF POSSIBLE. THE IDEA IS TO STAY TOWARD THE MIDDLE OF THE LATEST ENSEMBLE GUIDANCE WHICH IS CLOSEST TO A BLEND OF THE 00Z ECMWF/12Z UKMET...WITH THE UKMET LOOKING NEAR IDEAL WITH TIMING...BUT PERHAPS TOO DEEP GIVEN ITS PLACEMENT ON THE DEEPER SIDE OF THE LATEST ENSEMBLE SPREAD. SHORTWAVE ENTERING THE PACIFIC NORTHWEST SUN REINFORCING THE DEEP SOUTHWEST TROUGH THROUGH TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 12Z NAM BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE ENSEMBLE AND DETERMINISTIC TRENDS HAVE BEEN TO SHOW MORE SEPARATION BETWEEN THE BASE OF THE UPPER TROUGH ACROSS THE CNTRL U.S. ON 12Z/17 AND THE BROAD UPPER LOW OVER BAJA MEXICO. GIVEN THESE TRENDS...THE 00Z ECMWF APPEARS TOO FAR NORTH WITH THE BASE OF THE TROUGH/POSSIBLE CLOSED LOW OVER NWRN MEXICO WITH THE 00Z UKMET/CMC PERHAPS ON THE OTHER EXTREME WITH THE POSITION FARTHEST SOUTH. THE 12Z ECMWF/UKMET/CMC SUPPORT THE PREVIOUS PREFERENCE NEAR THE 12Z GFS...WITH THE LATEST DETERMINISTIC MODELS SHOWING SIMILARLY OUTSIDE OF THE SOMEWHAT FASTER 12Z NAM...WITH A GOOD MIDDLE GROUND NEAREST TO THE CENTER OF THE LATEST ENSEMBLE SPREAD. SHORTWAVES IN FAST FLOW ACROSS THE PACIFIC NORTHWEST MON/TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/00Z ECMWF BLEND CONFIDENCE: BELOW NORMAL COMPLEX INTERACTION ACROSS THE PACIFIC TOWARD THE PACIFIC NORTHWEST COAST AND BRITISH COLUMBIA MAKE FOR A LOW CONFIDENCE FORECAST. WHILE THE 12Z GFS HAS BEEN TRENDING WEAKER AND NORTH WITH A SHORTWAVE NEARING THE QUEEN CHARLOTTE ISLANDS JUST OFF OF THE CNTRL BRITISH COLUMBIA COAST...IT REMAINS RATHER DEEP COMPARATIVELY. THE 12Z CMC IS NO LONGER OUT OF PHASE WITH THE REMAINING GUIDANCE AS WAS ITS 00Z RUN. THE 12Z ECMWF IS TOWARD THE SOUTH SIDE WITH LOWER HEIGHTS OFF OF THE PACIFIC NORTHWEST COAST 12Z/17 COMPARATIVELY. GIVEN LARGE SPREAD...THE 00Z ECMWF AND 12Z NAM SHOW TWO POSSIBLE SOLUTIONS WITH A BLEND IN THE MIDDLE APPEARING LIKE THE BEST COMPROMISE AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO