MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 140 AM EST MON FEB 02 2015 VALID FEB 02/0000 UTC THRU FEB 05/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 00Z MODEL GUIDANCE ALONG WITH FINAL PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 00Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...AMPLIFIED TROF MOVING FROM THE UPPER GREAT LAKES TOWARD NEW ENGLAND THROUGH 03/0600Z... ...STRENGTHENING SURFACE LOW... FINAL PREFERENCE: MODEL COMPROMISE BETWEEN THE 00Z ECMWF/CMC AND THE 12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: AVERAGE A BROAD AXIS OF HEIGHT FALLS WILL CONTINUE TO MARCH EASTWARD TOWARD THE OH VALLEY SPREADING AN EXTENSIVE AXIS OF SNOW FROM THE UPPER GREAT LAKES TO NEW ENGLAND. LOOKING AT THE SURFACE...THE 00Z NAM/UKMET REMAIN THE ONLY SOLUTIONS SUPPORTING A DUAL-LOW STRUCTURE WHILE ADVANCING FROM THE MID-ATLANTIC TO NEW ENGLAND. AS THE SURFACE WAVE GATHERS STRENGTH JUST OFFSHORE OF MA...THERE IS SOME SPREAD IN THE LOW PLACEMENT WITH THE 00Z ECMWF/CMC SITTING ON THE SOUTHWESTERN FLANK OF THE DETERMINISTIC GUIDANCE. THE ENSEMBLE LOW PLOT SUPPORTS THIS SOLUTION A BIT MORE READILY...PARTICULARLY THE 12Z ECMWF ENSEMBLE MEMBERS. THE WPC PREFERENCE IS A MODEL COMPROMISE BETWEEN THE 00Z ECMWF/CMC AND 12Z ECMWF ENSEMBLE MEAN. ...SLOW-MOVING UPPER LOW AFFECTING MX THROUGH TUESDAY... ...EVENTUAL OPEN WAVE CROSSING THE DEEP SOUTH... FINAL PREFERENCE: A NON-00Z CMC MODEL SOLUTION FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN UPPER TROF INITIALLY CENTERED OVER SOUTHERN BAJA CA WILL GRADUALLY NOSE EASTWARD MOVING THROUGH MX DURING MUCH OF THE PERIOD. THE GUIDANCE SHOWS THIS CLOSED LOW SHOULD BE LOCATED OVER CENTRAL MX ON TUESDAY MORNING BEFORE LIFTING ACROSS THE RIO GRANDE BY 04/0000Z. AT THIS TIME...THE BIGGEST OUTLYING SOLUTION IS THE 00Z CMC WHICH IS DISPLACED TO THE SOUTH. GENERALLY SPEAKING...THE 00Z NAM/GFS/UKMET/ECMWF AGREE REASONABLY WITH THIS SCENARIO AS THE 00Z CMC LAGS TO THE SOUTH AND WEST. GIVEN THIS ASSESSMENT...A NON-00Z CMC SOLUTION IS RECOMMENDED. ...UPPER TROF DIGGING INTO THE UPPER MIDWEST BY 04/1200Z... ...ASSOCIATED PROGRESSIVE COLD FRONT... FINAL PREFERENCE: BLEND OF THE 00Z CMC/12Z ECMWF WITH THE 12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: BELOW AVERAGE THE FLOW WILL BEGIN TO AMPLIFY AGAIN OVER THE NORTHERN TIER OF THE CONUS BY MID-WEEK AS A BAND OF HEIGHT FALLS DIVES THROUGH THE UPPER MIDWEST BY WEDNESDAY MORNING. AS WAS THE CASE YESTERDAY...THE 00Z NAM IS THE SLOWEST TO BRING THE TROF INTO THE UPPER MIDWEST WHICH IS IN STARK CONTRAST WITH THE 21Z SREF MEAN WHICH IS MORE PROGRESSIVE IN NATURE. THE SPREAD AMONGST THE MODELS CONTINUES TO GROW THEREAFTER...PARTICULARLY WITH THE 00Z NAM RELATIVE TO THE 00Z GEFS/21Z SREF MEANS. THE 00Z GFS REMAINS THE QUICKEST SOLUTION WHILE A MAJORITY OF THE LATEST 00Z GUIDANCE HAVE STAYED ON THE SLOWER SIDE OR AT LEAST CLOSER TO THE CENTER OF THE SPREAD. OVERALL...THE 00Z ECMWF TRENDED A BIT SLOWER ON DAY 3 RELATIVE TO ITS PREVIOUS RUN. THIS ACTUALLY TAKES IT CLOSER TO THE SLOWER 00Z ECMWF. WOULD PREFER TO STICK WITH THE PREVIOUS PREFERENCE AT THIS TIME WHILE INCORPORATING THE LATEST 00Z CMC TO THE MIX. THAT IS A COMBINATION OF THE 00Z CMC/12Z ECMWF WITH THE 12Z ECMWF ENSEMBLE MEAN. UNTIL THE SPREAD BEGINS TO DIMINISH SOME...WILL HAVE TO LEAN ON THIS FORECAST APPROACH. ...SERIES OF WEAK LOW-AMPLITUDE WAVES RACING ACROSS THE NATION... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: AVERAGE A FLATTENING UPPER RIDGE ACROSS THE EASTERN PACIFIC WILL GIVE WAY TO A SERIES OF LOW-AMPLITUDE WAVES WHICH WILL RACE ACROSS THE COUNTRY. THERE IS SOME VARIANCE NOTED IN THE SOLUTIONS BUT MOST DIFFERENCES ARE SMALL IN NATURE. FEEL A GENERAL MODEL COMPROMISE WILL SUFFICE TO HANDLE SUCH LOW-AMPLITUDE DIFFERENCES. ...BROAD TROF REACHING THE EASTERN PACIFIC BY 05/1200Z... ...DEEP SURFACE CYCLONE... FINAL PREFERENCE: BLEND OF THE 00Z GEFS/12Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: BELOW AVERAGE AS THE UPPER PATTERN BEGINS TO GATHER MORE AMPLITUDE OVER THE EASTERN PACIFIC...THE GUIDANCE DIVERGE IN THE EXACT TIME OF THIS SCENARIO. THE 540-DM SPAGHETTI PLOTS SHOW A GREAT DEAL OF VARIATION IN THE SOLUTIONS WHICH LEADS TO THE COMPLEXITIES AT HAND. WILL CONTINUE TO SPLIT THE DIFFERENCE BETWEEN THE 00Z GEFS/12Z ECMWF ENSEMBLE MEANS SOLUTIONS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER