MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 223 AM EST WED FEB 15 2017 VALID FEB 15/0000 UTC THRU FEB 18/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION AND FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...WEAKENING CLOSED LOW MOVING ACROSS THE LOWER MS VALLEY TONIGHT LOW PRESSURE CROSSING THE GULF COAST STATES... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL CONSENSUS CONFIDENCE: SLIGHTLY ABOVE AVERAGE LATE EVENING WV/IR SAT IMAGERY FEATURES SHEARING/OPENING MID-LEVEL TROUGH OVER THE LOWER MISSISSIPPI RIVER VALLEY...WITH GOOD MODEL AGREEMENT WITH CONTINUED DAMPENING OF THIS FEATURE THROUGH EARLY THURSDAY...BEFORE IT SLIDES OFFSHORE OF THE SOUTHEAST COAST. THE 00Z NAM HAS SLOWED DOWN ITS PROGRESSION OF THE SURFACE LOW TO THE POINT THAT IT IS NOW COMPARABLE TO THE REST OF THE AVAILABLE GUIDANCE...INCLUDING THE 00Z GFS. ALOFT...MODELS HANDLE FEATURE MASS FIELD COMPARABLY. A GENERAL MODEL BLEND ALIGNS WELL WITH THE LATEST ENSEMBLE GUIDANCE. 07Z UPDATE: ECMWF HAS TRENDED TOWARDS A WEAKER SURFACE FEATURE AT 00Z...IN LINE WITH THE REST OF GUIDANCE. NO CHANGES MADE TO PREFERENCES. ...CLOSED LOW DEVELOPMENT OVER THE GREAT LAKES/NORTHEAST THROUGH WED... ...SURFACE LOW ENTERING THE NORTHEAST AND REDEVELOPING OFFSHORE OF THE NEW ENGLAND COAST LATE TODAY THROUGH THURSDAY... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z NAM/ECMWF/UKMET CONFIDENCE: ABOVE AVERAGE ALOFT...THE 00Z NAM HAS SLOWED SLIGHTLY TOWARD THE REST OF THE GUIDANCE ENVELOPE WITH RESPECT TO THE EJECTING UPPER LOW FROM THE NEW ENGLAND COAST TOWARD ATLANTIC CANADA...BUT REMAINS A STRONG OUTLIER WITH THE UPPER LOW. THE 12Z UKMET/ECMWF AND NEW 00Z GFS ARE IN DECENT AGREEMENT WITH UPPER FEATURES. HOWEVER...THE 00Z GFS HAS NUDGED A BIT FARTHER SOUTH AND MORE PROGRESSIVE/OFFSHORE TOWARD THE ECENS AND 12Z/ECMWF. HAVE THEREFORE CONTINUED A PREFERRED BLEND 12Z ECMWF/UKMET...WHICH MESHES WELL WITH THE 12Z/ECENS. 07Z UPDATE: THE 00Z ECMWF AND 00Z/CMC HAVE EACH FOLLOWED THE TREND OF THE 00Z GFS AND TRENDED A BIT SOUTH AND QUICKER FROM THEIR PREVIOUS RUNS...AND ARE NOW IN GOOD AGREEMENT. THE ECMWF...UKMET AND NAM CAMP REMAIN STRONGEST WITH THE SURFACE LOW...WHICH CLUSTERS WELL WITH ENSEMBLE SURFACE LOWS AND THE EC ENS MEAN. WILL ADD THE NAM TO THE PREFERRED BLEND AT ABOVE AVERAGE CONFIDENCE. ...SERIES OF STORMS INTO THE PACIFIC NORTHWEST AND NRN CALIFORNIA THROUGH THU... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/NAM/ECMWF CONFIDENCE: AVERAGE TIMING DIFFERENCES HAVE EASED TO SOME DEGREE WITH THE 00Z NCEP SUITE...BUT STRENGTH OF THE UPPER SYSTEM AND SFC TROUGH/FRONT VARIES SLIGHTLY...WITH THE GFS FARTHEST NORTH/ECMWF FARTHEST SOUTH AND 00Z NAM (AND NAM PARALLEL) IN THE MIDDLE GROUND BOTH SPATIALLY AND IN TERMS OF INTENSITY OF THE SURFACE LOW. A BLENDED SOLUTION OF THESE THREE MODELS WILL BE USED TO REFLECT MODEL CONSENSUS AT THIS TIME...THOUGH WITH MODEL DISCONTINUITY...WILL KEEP FORECAST CONFIDENCE LOWER THAN AVERAGE. 07Z UPDATE: ECMWF HAS TRENDED FARTHER NORTH TOWARDS THE 00Z GFS SOLUTION...AND HAS ABANDONED THE DOUBLE BARREL LOW IDEA OF PREVIOUS RUNS. 00Z UKMET HAS COME FARTHER SOUTH AND IS REASONABLY ALIGNED WITH THE ECMWF WITH THIS FEATURE. MEANWHILE...00Z CMC CAME IN SIMILARLY ALIGNED BUT WEAKER...AND REMAINS ON THE SLOW SIDE OF THE GUIDANCE ENVELOPE. WILL UPDATE BLEND TO ACCOUNT FOR 00Z ECMWF AT AVERAGE CONFIDENCE TO REFLECT CONVERGING SOLUTIONS. ...SHARPENING UPPER TROUGH WEST OF CALIFORNIA FRI/SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS / ECMWF CONFIDENCE: SLIGHTLY BELOW AVERAGE MODELS CONTINUE TO TREND A BIT SLOWER AND STRONGER WITH POTENT UPPER LOW DIGGING SOUTH ACROSS CALIFORNIA FRIDAY NIGHT THROUGH SATURDAY. THE 00Z GFS AND 18Z GEFS IS STRONGER WITH THE UPPER LOW THAN THE 12Z ECMWF (AND ECENS)...WITH THE GFS DEPICTING A CLOSED LOW BY THE END OF THE PERIOD SATURDAY MORNING. THE 12Z CMC IS AT THE FAST END OF THE GUIDANCE ENVELOPE BUT IS CLOSE TO THE GFS WITH THE INTENSITY OF THE UPPER LOW. THE NAM IS ON THE OUTER FRINGE OF ITS USEFUL RANGE WITH THIS FEATURE...BUT FOR THE RECORD IS A DECENT FIT IN BETWEEN THE FASTER CMC AND SLOWER/STRONGER GFS. KEEPING IN MIND THAT THE MODEL ENSEMBLES ARE TRENDING IN A SLOWER DIRECTION...WOULD PREFER TO LEAN TOWARD THE SLOWER SIDE OF THE GUIDANCE ENVELOPE. WILL THEREFORE BLEND LATEST ECMWF AND GFS ALONG WITH THEIR MEMBER ENSEMBLES. GIVEN LARGE ENSEMBLE LOW DIFFERENCES AND POORER THAN AVERAGE RUN TO RUN CONSISTENCY...CONFIDENCE REMAINS BELOW AVERAGE. 07Z UPDATE: 00Z ECMWF FOLLOWED GFS TREND TOWARDS A STRONGER SYSTEM FOR LATE WEEK. GFS REMAINS SLIGHTLY FASTER THAN THE ECMWF WITH THE SURFACE LOW AND FRONT THROUGH FRIDAY AFTERNOON...BUT 00Z ECMWF CATCHES UP BY SATURDAY MORNING. WILL UPDATE BLEND TO REFLECT NEW 00Z ECMWF AT SLIGHTLY BELOW AVERAGE CONFIDENCE. ...UPPER TROUGH OVER THE SOUTHERN PLAINS/NORTHERN MEXICO BY THU-FRI... ...SYSTEM EJECTING EAST ACROSS THE DEEP SOUTH FRI/SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS & ECMWF CONFIDENCE: ABOVE AVERAGE GOOD MODEL AGREEMENT WITH CARVING OUT ANOTHER CLOSED LOW DIGGING ACROSS NW MEXICO...AGAIN WITH SHORTWAVE ENERGY EJECTING NE AND DAMPENING ACROSS THE ARKLATEX INTO THE GULF COAST FRI/SAT. THE 00Z NAM REMAINS AN OUTLIER TO THE SOUTH WITH THE UPPER LOW COMPARED TO THE REMAINING DETERMINISTIC GUIDANCE...A SOLUTION WHICH IS NOT SUPPORTED AT THIS TIME. THE LATEST 12Z UKMET/CMC HAVE SLOWED SIGNIFICANTLY FROM THEIR PREVIOUS RUNS BUT REMAIN SLIGHTLY FASTER WITH RESPECT TO THE LATEST ENSEMBLE SPREAD CONCERNING THE UPPER LOW PROGRESSION THROUGH THE SRN PLAINS FRI EVENING. THE 12Z ECMWF AND ITS ENSEMBLES ARE SLOWER WITH THE 12Z ECMWF NUDGING SLIGHTLY AHEAD OF ITS 00Z RUN. THE 00Z GFS HAS PROJECTED MASS FIELDS SIMILARLY AND MESHES WELL WITH ITS MEMBER ENSEMBLES AND IS CLOSE TO THE 12Z ECENS. PENDING ARRIVAL OF THE 00Z ECMWF...WILL MAINTAIN PREFERENCE FOR A GFS/ECMWF BLEND AT ABOVE AVERAGE CONFIDENCE. 07Z UPDATE: 00Z ECMWF REMAINS A TOUCH SLOWER/STRONGER WITH THE EJECTING SHORTWAVE ENERGY ACROSS THE SOUTHERN PLAINS THROUGH 12Z/FRIDAY...BUT CATCHES UP TO THE 00Z/GFS SOLUTION BY THE END OF THE PERIOD. WILL CONTINUE PREVIOUS...ENSEMBLE SUPPORTED BLEND AT ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... MONTEFUSCO