MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 132 AM EST SUN FEB 01 2015 VALID FEB 01/0000 UTC THRU FEB 04/1200 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. ...UPPER LOW/DEVELOPED SURFACE CYCLONE DEPARTING FROM NEW ENGLAND... FINAL PREFERENCE: GENERAL MODEL COMPROMISE FORECAST CONFIDENCE: HIGH WATER VAPOR IMAGERY DEPICTED A NEGATIVELY-TILTED TROF CROSSING EAST OF NOVA SCOTIA. EVENTUALLY THIS SYSTEM BECOMES ABSORBED BY A BAND OF HEIGHT FALLS CURRENTLY MOVING THROUGH SOUTHWESTERN QUEBEC. MODELS SHOW SUFFICIENT AGREEMENT WHICH SUPPORTS A GENERAL MODEL COMPROMISE HERE. ...AMPLIFIED TROF MOVING FROM THE CENTRAL PLAINS TO THE NORTHEASTERN U.S. ON SUNDAY/MONDAY... ...STRENGTHENING FRONTAL WAVE... FINAL PREFERENCE: BLEND OF THE 00Z GFS/ECMWF FORECAST CONFIDENCE: AVERAGE A SERIES OF SHORTWAVES MOVING THROUGH THE CENTRAL PLAINS/MIDDLE MS VALLEY WILL QUICKLY GAIN AMPLITUDE AS AN UPSTREAM IMPULSE DROPS DOWN FROM THE NORTHERN ROCKIES. THIS AMPLIFIED TROF IS FORECAST TO RACE EASTWARD REACHING THE OH/TN VALLEYS BY 02/1200Z AS A SURFACE WAVE BEGINS TO GATHER STRENGTH. THE OVERALL EFFECT OF THIS SYSTEM WILL BE A BAND OF WINTRY PRECIPITATION FROM THE CENTER OF THE COUNTRY EASTWARD ACROSS THE UPPER GREAT LAKES/OH VALLEY AND INTO NEW ENGLAND. THROUGH THE FIRST 24 TO 36 HOURS...THE 00Z CMC IS A BIT SLOWER WITH THE PATTERN ALOFT WHICH LEADS TO A MORE WESTWARD DISPLACED SURFACE CYCLONE. FURTHER...THE 00Z NAM DEPICTS A DUAL-LOW STRUCTURE MOVING THROUGH THE MID-ATLANTIC ON MONDAY MORNING WHICH APPEARS TO BE A MINORITY SOLUTION. AND LIKE PREVIOUS DAYS...THE 12Z UKMET HAS SHOWN A BIAS TO BE ON THE NORTHERN SIDE OF THE SPREAD WHICH LEAVES THE 00Z GFS/ECMWF AS THE BEST COMBINATION OF MODELS TO UTILIZE. SUCH A SOLUTION FITS WELL IN THE ENSEMBLE LOW PLOT AND IS CONSISTENT WITH THE ENSEMBLE MEANS. ...SLOW-MOVING CLOSED LOW OVER MX... ...EVOLVING INTO AN OPEN WAVE ACROSS EASTERN MX BY 04/0000Z... FINAL PREFERENCE: BLEND OF THE 00Z GFS/ECMWF WITH THE 12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE AN EXPANSIVE NEGATIVE ANOMALY REMAINS A MAINSTAY FEATURE ACROSS MUCH OF MX THROUGHOUT THE FORECAST. THE 500-MB HEIGHTS OF THIS SYSTEM SUGGEST DEPARTURES ON THE ORDER TO 3 TO 3.5 STANDARDIZED ANOMALIES BELOW CLIMATOLOGY FOR EARLY FEBRUARY. SUCH ANOMALIES SHOULD CONTINUE BEFORE DIMINISHING AS THE CLOSED LOW BEGINS TO OPEN UP LATE IN THE PERIOD. THROUGH 02/1200Z...MODELS ARE IN REASONABLE AGREEMENT BEFORE TIMING DIFFERENCES EMERGE. ON THE QUICKER SIDE OF THE ENVELOPE ARE THE 00Z NAM/21Z SREF MEAN WHILE OTHER MODELS STAY OFF TO THE WEST. AS THE WAVE OPENS UP OVER EASTERN MX...THE 00Z GFS/ECMWF AND 12Z ECMWF ENSEMBLE MEAN END ON THE SLOWER SIDE. PLAN ON LEANING TOWARD THE SLOWER SIDE GIVEN THE FORECAST INVOLVES A CUT-OFF LOW. A BLEND OF THE 00Z GFS/ECMWF WITH THE 12Z ECMWF ENSEMBLE MEAN IS RECOMMENDED. ...LOW-AMPLITUDE WAVES MOVING THROUGH THE PACIFIC NORTHWEST THROUGHOUT THE PERIOD... FINAL PREFERENCE: THROUGH DAY 2: GENERAL MODEL COMPROMISE...THEREAFTER: A NON-00Z ECMWF/12Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: AVERAGE AT THE START OF THE PERIOD...AN UPPER RIDGE WILL ANCHOR THE PACIFIC NORTHWEST AND CENTRAL GREAT BASIN. THIS RIDGE AXIS IS FORECAST TO GRADUALLY FLATTEN AS A SERIES OF LOW-AMPLITUDE WAVES TRAVEL THROUGH THE PACIFIC NORTHWEST AND EVENTUALLY INTO INTERIOR LOCATIONS. THE FLAT NATURE OF EACH WAVE CREATES A SLEW OF DIFFERENCES AMONG THE MODELS. THROUGH DAY 2...FEEL A GENERAL MODEL COMPROMISE WILL SUFFICE. BY DAY 3...ALL OF THE GUIDANCE SHOWS AN UPPER RIDGE DEVELOPING ACROSS THE EASTERN PACIFIC WITH THE EXCEPTION OF THE 00Z ECMWF/12Z ECMWF ENSEMBLE MEAN WHICH FLATTENS THE RIDGE. WILL FAVOR A NON-00Z ECMWF/12Z ECMWF ENSEMBLE MEAN FOR DAY 3. ...UPPER TROF CROSSING THE UPPER MIDWEST BY WEDNESDAY MORNING... ...ATTENDANT COLD FRONT MOVING THROUGH THE CENTER OF THE CONUS... FINAL PREFERENCE: BLEND OF THE 00Z GFS/ECMWF FORECAST CONFIDENCE: AVERAGE TOWARD THE END OF THE PERIOD...A BROAD AXIS OF HEIGHT FALLS MOVE THROUGH THE UPPER MIDWEST AS A STRONG UPPER TROF CROSSES OVERHEAD. TIMING DIFFERENCES ARE NOTED WITH THE 00Z NAM BEING DECIDEDLY SLOWER THAN ANY OTHER DETERMINISTIC/ENSEMBLE SOLUTIONS. THERE IS SOME SPREAD IN THE ENSEMBLE MEANS WITH THE 12Z ECMWF ENSEMBLE MEAN BEING QUICKER THAN THE 00Z GEFS MEAN. IT IS WORTH NOTING THE 00Z GFS HAD TRENDED TOWARD THE QUICKER ECMWF ENSEMBLE MEAN SOLUTION WHILE THE 00Z ECMWF JUST SLOWED DOWN TO LOOK MORE LIKE THE 00Z GEFS MEAN. AT THIS POINT SPLITTING THE DIFFERENCE BETWEEN THESE TWO SOLUTIONS SEEMS TO BE THE BEST APPROACH. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER