MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 145 PM EST FRI FEB 13 2015 VALID FEB 13/1200 UTC THRU FEB 17/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING FINAL PREFERENCES UPPER TROUGH APPROACHING THE PACIFIC NORTHWEST TONIGHT DOWNSTREAM AMPLIFICATION INTO THE PLAINS BY SUN- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: AVERAGE DIFFERENCES HERE ARE RELATIVELY SMALL BUT THE 12Z NAM IS FASTEST OF THE DETERMINISTIC MODELS...WHILE THE 00Z UKMET IS MORE AMPLIFIED. BOTH THE 00Z ECMWF/CMC ARE SLOWER...WITH THE 12Z GFS SITTING IN THE MIDDLE REGARDING TIMING. A BLEND OF THE SIMILAR GFS/ECMWF SHOULD HELP TO RESOLVE TIMING DIFFERENCES...WITH THE 12Z CMC OFFERING UP A SECOND OPTION...AS IT IS SIMILAR TO THE 12Z ECMWF. THE ENSEMBLES SUPPORT THE GFS/ECMWF AS WELL...MORE SO THAN THE OTHER GUIDANCE AT THIS TIME. POWERFUL UPPER TROUGH/VORTEX CROSSING THE GREAT LAKES AND NORTHEAST INTENSE SURFACE LOW DEVELOPMENT OFF NEW ENGLAND ON SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM...12Z GFS..12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THERE HAS BEEN CONVERGING OF SOLUTIONS SINCE YESTERDAY WITH THE CURRENT MODELS IN DECENT AGREEMENT ON THE TIMING AND STRENGTH OF A POWERFUL CLOSED LOW FORECAST TO PASS JUST SOUTH OF NEW ENGLAND. CURRENTLY...THE 12Z NAM/12Z GFS/12Z ECMWF ARE IN CLOSE AGREEMENT ON THE STRENGTH AND POSITION OF THE RESULTING SURFACE LOW. THE 12Z GFS IS CLOSEST TO THE COAST WTIH THE SURFACE LOW...LIKELY TOO CLOSE...BUT A 3-WAY BLEND OF THE NAM/GFS/ECMWF APPEARS BEST AS EACH MODEL HAS SMALL DIFFERENCES FROM ONE ANOTHER...BUT TOGETHER REPRESENT A GOOD COMPROMISE. THE 12Z UKMET/CMC REMAIN A BIT FARTHER OUT TO SEA OR WEAKER...AND THEREFORE WILL NOT BE INCLUDED IN THE COMPROMISE. CLOSED UPPER LOW MEANDERING OFF OF THE BAJA PENINSULA THROUGH MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 12Z UKMET COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE HAS BROAD AGREEMENT WITH THIS SYSTEM...BUT BY SUN NIGHT...THE UKMET SHOWS A MORE STRONGLY DIGGING UPPER TROUGH THROUGH THE WEST COMPARED TO THE REMAINING MODEL CONSENSUS. THIS ENDS UP INTERACTING WITH THE CLOSED LOW OFF NEAR THE BAJA PENINSULA...KICKING IT OUT TOWARD THE EAST FASTER WITH THE UKMET MODEL. THEREFORE...GIVEN A LACK OF SUPPORT FOR THE UKMET AT THIS TIME...A NON 23Z UKMET COMPROMISE IS PREFERRED. SHORTWAVE ENERGY DIVING THROUGH THE INTERIOR WEST ON MON DOWNSTREAM SURFACE WAVE DEVELOPING ALONG THE GULF COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF CONFIDENCE: SLIGHTLY BELOW AVERAGE THE MODELS ARE IN GOOD AGREEMENT WITH A SHORTWAVE ROUNDING THE TOP OF A STRENGTHENING RIDGE JUST OFF THE WEST COAST...WITH THE ENERGY THEN DIGGING DOWN THROUGH SOUTHWEST CANADA AND INTO THE NORTHWEST BY EARLY MON. WITH THE EXCEPTION OF THE 00Z UKMET...DETERMINISTIC AND ENSEMBLE SPAGHETTI HEIGHT TRENDS HAVE BEEN FLATTER OVER THE PAST THREE OR FOUR 12/00Z CYCLES. THE UKMET HAD ACTUALLY BEEN TRENDING MORE AMPLIFIED WITH THIS SHORTWAVE...BUT HAS BACKED OFF SOME WITH ITS 12Z/13 CYCLE. HOWEVER...RATHER LARGE SPREAD REMAINS...WITH THE 12Z NAM...12Z GFS...AND EVEN THE 12Z CMC TO SOME EXTENT...SHOWING TOWARD THE FLATTER SIDE OF THE CURRENT ENSEMBLE DISTRIBUTION. DOWNSTREAM...A WEAK SURFACE LOW IS BEGINNING TO GET PICKED UP BY THE ENSEMBLE MEMBERS ACROSS THE DEEP SOUTH MON EVENING. THE 12Z UKMET...WHICH REMAINS ON THE DEEP EDGE OF THE LATEST ENSEMBLE SPAGHETTI HEIGHTS...IS NEARLY OUTSIDE OF THE LATEST SPREAD WHEN IT COMES TO A SURFACE LOW IT HAS DEPICTED OVER SRN TENNESSEE BY 00Z/17. THE 12Z ECMWF HAS BACKED OFF SLIGHTLY ON THE AMPLITUDE OUT WEST...WITH SOME MINOR ADJUSTMENTS DOWNSTREAM. THE 00Z ECMWF REMAINS THE CLOSEST TO THE GREATEST ENSEMBLE CLUSTERING AT THIS POINT...BUT IT IS UNKNOWN IF THE FLATTENING TREND WILL CONTINUE...REVERSE OR END. CONFIDENCE REMAINS LIMITED IN THE DETAILS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO