MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 103 PM EDT SUN MAR 29 2015 VALID MAR 29/1200 UTC THRU APR 02/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. SHORTWAVE TRACKING FROM THE UPPER MS VALLEY SUN TO NEW ENGLAND MON COLD FRONT REACHING THE EAST COAST MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 00Z ECMWF/12Z GFS CONFIDENCE: AVERAGE THERE IS REASONABLY GOOD AGREEMENT WITH THIS SYSTEM THROUGH MONDAY EVENING ALTHOUGH THE NAM BEGINS TO STRAY FROM THE CONSENSUS WITH A MUCH WEAKER SURFACE LOW OVER SRN QUEBEC. THE MAJORITY OF THE MODELS HAVE TRENDED QUICKER WITH THE UPPER TROUGH INTO TUESDAY MORNING...EXCEPT THE NAM WHICH HAS SLOWED SIGNIFICANTLY SINCE YESTERDAY AND IS THE SLOWEST OF THE DETERMINISTIC MODELS. CURRENTLY...THE ENSEMBLE MEANS ARE AHEAD OF THE NAM BUT SLIGHTLY BEHIND THE 12Z GFS AND 00Z ECMWF. HOWEVER...THE 12Z GFS AND 00Z ECMWF REPRESENT A GOOD MIDDLE GROUND WITH RESPECT TO THE ENSEMBLE/DETERMINISTIC SPREAD. SHORTWAVE CROSSING THE UPPER MS VALLEY/GREAT LAKES MON INTO TUE SURFACE LOW CROSSING THE MID ATLANTIC STATES TUE NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 2/3 WEIGHT 12Z GFS...1/3 WEIGHT 00Z ECMWF CONFIDENCE: AVERAGE THE 12Z NAM IS THE FARTHEST NORTH WITH ITS MID-LEVEL SHORTWAVE OF THE DETERMINISTIC MODELS AND OUTSIDE OF THE ENSEMBLE LOW SPREAD WITH ITS SURFACE LOW BY TUE EVENING IN THE NRN MID-ATLANTIC REGION. THE SURFACE LOW FROM THE 12Z GFS FITS IN VERY NICELY IN THE MIDDLE OF THE ENSEMBLE LOW SPREAD BUT THE 00Z ECMWF IS ON THE FAR SOUTHWEST EDGE OF THE ECMWF MEMBERS. THE 00Z ECMWF COULD BE A BIT WEAK AND SLOW WITH THE MID-LEVEL SHORTWAVE BUT THE 12Z GFS HAS TRENDED STRONGER THAN THE AVERAGE DETERMINISTIC PIECE OF GUIDANCE. THE 00Z CMC/UKMET IS A STRONG/FLAT OUTLIER RESPECTIVELY. GIVEN FAVORABLE LOW PLACEMENT FROM THE 12Z GFS...THOUGH PERHAPS A BIT TOO STRONG...IT IS RECOMMENDED TO BLEND THE 12Z GFS WITH 00Z ECMWF...BUT WITH A LITTLE MORE WEIGHT ON THE GFS GIVEN THE ECMWF IS NOT IN A FAVORABLE LOW LEVEL POSITION. MID LEVEL TROUGH NEAR BAJA CA MON...CROSSING THE SOUTHERN PLAINS TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ PREFERENCE: 12Z GFS...00Z ECMWF...00Z CMC BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z GFS IS A LITTLE WEAKER THAN THE AGREEABLE 00Z ECMWF/CMC BUT ALL THREE SHOW A SIMILAR TIMING WITH THIS SHORTWAVE. THE 00Z UKMET IS BY FAR THE SLOWEST AND IS NOT CONTAINED WITHIN THE ENSEMBLE SPREAD. THE 12Z NAM IS NOT PREFERRED AS IT TAKES THE CORE OF THE MID-LEVEL ENERGY...WHEN IT REACHES THE PLAINS TUE MORNING...NORTH OF THE REMAINING CONSENSUS. LONG WAVE TROUGH OFF THE PACIFIC NORTHWEST COAST MON SHORTWAVE/COLD FRONT APPROACHING THE NORTHERN PLAINS TUE NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/00Z ECMWF BLEND CONFIDENCE: AVERAGE THE MODELS SHOW GOOD AGREEMENT THROUGH DAY 2...00Z/01...AT WHICH POINT SOME MINOR DIFFERENCES IN STRENGTH/TIMING APPEAR. THE QUASI-AMPLIFIED NATURE OF THE NRN STREAM WOULD IMPLY THE 00Z CMC IS TOO FAST AS IT ALSO LIES ON THE FASTER SIDE OF THE DETERMINISTIC GUIDANCE. BY WED EVENING...THE GEFS/GFS ARE A BIT FASTER THAN THE ECMWF/EC ENSEMBLES REGARDING THE 540 DM HEIGHT LINE...WITH A BLEND OF THE TWO APPEARING TO BE THE MOST LIKELY SCENARIO AT THIS TIME. THE GFS/ECMWF BLEND IS ALSO MOST AGREEABLE TO THE ENSEMBLE LOW CLUSTERING SEEN FROM THEIR MOST RECENT RUN. SHORT WAVE APPROACHING THE PACIFIC NORTHWEST EARLY WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF/00Z UKMET CONFIDENCE: SLIGHTLY BELOW AVERAGE CONFLICTING TRENDS MAKE FOR A DIFFICULT FORECAST WITH THIS FEATURE BUT IT APPEARS THE 12Z NAM/GFS ARE TOO SLOW GIVEN REASONABLY GOOD ENSEMBLE SPAGHETTI HEIGHT SUPPORT FOR A FASTER SOLUTION...NEAR THE 00Z ECMWF/00Z ECMWF MEAN. THE 00Z UKMET AGREES WITH THE 00Z ECMWF BUT THE 00Z CMC IS ON THE WEAKER SIDE OF THE GUIDANCE DESPITE APPARENT GOOD TIMING. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO