MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 154 PM EST THU FEB 05 2015 VALID FEB 05/1200 UTC THRU FEB 09/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO IMPACT THEIR SHORT RANGE FORECASTS. SWLY FLOW AND EMBEDDED SHORTWAVES ACROSS THE NW THROUGH SUN MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: SLIGHTLY BELOW AVERAGE THROUGH SUN MORNING...12Z/08...THE DETERMINISTIC/ENSEMBLE GUIDANCE SHOWS SOUTHWESTERLY FLOW IN THE MID LEVELS ACROSS THE WEST COAST WITH EMBEDDED SHORTWAVE IMPULSES COMING ASHORE. THESE IMPULSES ARE HARD TO TRACK ON AN INDIVIDUAL BASIS THROUGH THE WEEKEND...AND THE MODELS HAVE SHOWN SOME RUN TO RUN VARIABILITY OVER THEIR PAST FEW CYCLES...AND WITH EACH OTHER CONSIDERING THE MOST RECENT GUIDANCE. SOME MODEL DIFFERENCES NOTED INCLUDE THE NAM/SREF HAVING ROUGHLY 10-15 KTS WIND STRONGER IN THE 850-700 MB LAYER INTO THE WEST COAST DURING THE DAY ON FRI...AND THE 00Z ECMWF IS APPROXIMATELY 5-10 KTS WEAKER WITH THIS FLOW COMPARED TO AN AVERAGE OF THE REMAINING MODELS. HOWEVER...GIVEN THE RUN TO RUN CHANGES AND RESOLUTION CONSIDERATIONS...NO SINGLE DETERMINISTIC MODEL CAN BE RULED OUT. PERHAPS RESOLUTION OR AN ENSEMBLE OF MULTIPLE MODELS CAN BE CONSIDERED ACROSS THE WESTERN U.S. THROUGH SUN MORNING. LIKELY CLOSED LOW APPROACHING THE WEST COAST SUN NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS / 00Z ECMWF COMPROMISE CONFIDENCE: AVERAGE THE 12Z UKMET STANDS OUT AS BEING FASTER AND FARTHER NORTH WITH THE CENTER OF A LIKELY CLOSED LOW APPROACHING THE WEST COAST BY MONDAY MORNING. THE 12Z ECMWF/CMC HAVE TRENDED NORTH...AT LEAST SOME...COMPARED TO THEIR 00Z RUNS BUT THE REMAINING DETERMINISTIC AND ENSEMBLE MEAN GUIDANCE SUPPORTS A SOLUTION CLOSER TO THE NON 12Z UKMET MODELS. THE NAM/GFS COULD BE TOO SLOW/SOUTH WITH THE CLOSED LOW BY 00Z/09...SUN EVENING...BUT THE ENSEMBLES DO NOT SUPPORT THE FASTER UKMET AT THIS TIME. TOWARD THE MIDDLE IS A BLEND OF THE 12Z GFS AND 00Z ECMWF. CONFIDENCE IS ONLY AVERAGE GIVEN THE EXTENDED NATURE OF THE FORECAST AND POSSIBILITY OF CHANGES IN LATER MODEL RUNS CONSIDERING THE CURRENT ENSEMBLE SPREAD WHICH LEAVES ROOM FOR ADJUSTMENTS EITHER NORTH OR SOUTH OF THE NON UKMET CONSENSUS. FRONT EXTENDING FROM THE NRN HIGH PLAINS TO THE MIDWEST AND LIKELY SURFACE LOW TRACKING EAST THROUGH THE OHIO VALLEY ON SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF/UKMET COMPROMISE CONFIDENCE: SLIGHTLY BELOW AVERAGE FROM SAT INTO SUN...THE 12Z NAM IS SIGNIFICANTLY NORTH WITH A SURFACE LOW ALONG A FRONTAL BOUNDARY EXTENDING NORTHWEST TO SOUTHEAST ACROSS THE N-CNTRL CONUS. THE ENSEMBLES SUPPORT A NON NAM BLEND HERE. BY THE END OF THE WEEKEND...THERE APPEARS TO BE SEVERAL VORTICITY MAXIMA AMPLIFYING DOWNSTREAM OF A RIDGE CENTERED OVER THE ROCKIES. THE MEAN UPPER TROUGH AXIS IN THE 12Z GFS/UKMET/CMC IS A BIT EAST OF THE ENSEMBLE MEANS AND 12Z NAM/ECMWF. THE GEFS/ECMWF ENSEMBLES SUPPORT A MIDDLE GROUND AT THIS TIME...WITH THE GFS/ECMWF/UKMET REPRESENTING A MIDDLE OF THE ROAD BLEND EMBEDDED WITHIN RELATIVELY BROAD ENSEMBLE SPREAD REGARDING THE UPPER TROUGH AND CORRESPONDING SURFACE LOW. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO