MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 245 AM EDT SUN MAR 29 2015 VALID MAR 29/0000 UTC THRU APR 01/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. LONGWAVE TROUGH DEPARTING THE EAST COAST ON SUN DEEPENING SURFACE LOW TRACKING UP EAST OF NOVA SCOTIA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THERE IS NOT MUCH MODEL SPREAD WITH THIS SYSTEM...AT THE SURFACE OR ALOFT. SINCE REMAINING IMPACTS TO THE UNITED STATES ARE MINIMAL...A GENERAL MODEL COMPROMISE IS PREFERRED. 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/00Z GFS CONFIDENCE: SLIGHTLY BELOW AVERAGE ON DAY 1...THERE IS LITTLE SPREAD AMONG MODEL CONCERNING THE TRACK AND STRENGTH OF THE SHORT WAVE. IN FACT...BOTH THE 00Z NAM AND GFS COULD BE ADDED TO THE PREFERENCE FOR THAT DAY. HOWEVER...BOTH THE 00Z NAM AND GFS (AS WELL AS THE 00Z UKMET) SPED UP ON DAY 2 AND DAY 3. THE 00Z CMC IS NOW CLOSER TO THE CONSENSUS POSITION...BUT STILL TOO SLOW WITH THIS SYSTEM. THE 00Z ECMWF JOINED THE PACK WITH A FASTER SOLUTION...AS DOES THE 00Z UKMET (WHICH BECOMES THE EASTERNMOST OUTLIER DURING DAY 3). BASED ON THE ABOVE...THE FASTER SOLUTION IS NOW PREFERRED...WITH A BLEND OF THE 00Z ECMWF/GFS REPRESENTING THE BEST CLUSTERING. SHORTWAVE CROSSING THE UPPER MS VALLEY/GREAT LAKES MON INTO TUE SURFACE LOW CROSSING THE MID ATLANTIC STATES TUE NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/12Z ECMWF CONFIDENCE: SLIGHTLY BELOW AVERAGE THE 00Z NAM BECOMES FASTER AND DEEPER WITH THIS SYSTEM...BEGINNING ON DAY 1 AND CONTINUES THE TREND THROUGH TUE (ITS SURFACE LOW IS ALSO THE FURTHEST NORTH BY THE END OF DAY 3). THE 00Z GFS HAS COME BACK TO THE PACK WITH RESPECT TO SPEED...THOUGH IT CONTINUES TO BE ON THE NORTHERN EDGE OF THE CONSENSUS ENVELOPE. THE 00Z UKMET CONTINUES TO BE FLAT...WHILE THE 00Z CMC TIMING LOOKS GOOD...BUT BECOMES MUCH DEEPER WITH THE SHORT WAVE DURING DAY 3 OFF THE EAST COAST. THE 00Z ECMWF CONTINUES TO BE THE SOUTHERNMOST SOLUTION WITH THIS SHORT WAVE...ESPECIALLY DURING DAY 2 WITH ITS PRECIPITATION SWATH. THE 12Z ECMWF WAS A BETTER FIT (THOUGH STILL FURTHER SOUTH THAT THE 00Z GFS). AT THIS POINT...THE 00Z ECMWF IS TOO FAR SOUTH TO KEEP IN THE PREFERENCE BLEND...AND THE 12Z ECMWF SOLUTION IS RETAINED. HOWEVER...DUE TO THE DIFFERENCES MENTIONED ABOVE...FORECAST CONFIDENCE HAS BEEN DROPPED TO SLIGHTLY BELOW AVERAGE. MID LEVEL TROUGH NEAR BAJA CA MON...CROSSING THE SOUTHERN PLAINS TUE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ PREFERENCE: NON 00Z UKMET BLEND CONFIDENCE: ABOVE AVERAGE THE 00Z NAM/GFS/00Z CMC/00Z ECMWF ARE CLOSE TO THE CONSENSUS WITH THE POSITION AND STRENGTH OF THE MID LEVEL TROUGH TRACKING ACROSS BAJA CA MON...WHICH THEN CROSSES THE SOUTHERN PLAINS TUE. THE 00Z UKMET CONTINUES TO LAG BEHIND THE CONSENSUS THROUGHOUT THE PERIOD...AND BECAUSE OF THIS CANNOT BE INCLUDED IN THE PREFERENCE. LONG WAVE TROUGH OFF THE PACIFIC NORTHWEST COAST MON SHORTWAVE/COLD FRONT APPROACHING THE NORTHERN PLAINS TUE NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 00Z NAM BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE THE 00Z NAM CONTINUES TO BE THE SLOW OUTLIER WITH THE SHORT WAVE THAT CROSSES THE PACIFIC NORTHWEST MON NIGHT INTO TUE...AND SLOWS A BIT MORE AS THE COLD FRONT WITH THE SHORT WAVE APPROACHES THE NORTHERN PLAINS. THE 00Z GFS APPEARS TO BE IN THE MIDDLE OF THE SPREAD WITH RESPECT TO THE SHORT WAVE TIMING AND PLACEMENT OF THE SURFACE FRONT TUE. THE 00Z UKMET HAS SLOWED CONSIDERABLY (COMPARED TO ITS 12Z SOLUTION)...AND IS NOW ON THE SLOWER SIDE OF THE GUIDANCE SUITE...ESPECIALLY WITH THE SURFACE FRONT APPROACHING THE NORTHERN PLAINS. BECAUSE OF THE LARGE CHANGE IN THE 00Z UKMET SOLUTION...IT IS NO LONGER PART OF THE PREFERRED BLEND. THE 00Z ECMWF IS ALSO A BIT SLOWER WITH ITS SOLUTION AT THE SURFACE AND IN THE MID LEVELS...BUT REMAINS CLOSE ENOUGH TO THE CONSENSUS TO RETAIN IN THE BLEND. SHORT WAVE APPROACHING THE PACIFIC NORTHWEST LATE TUE NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF/00Z GFS CONFIDENCE: BELOW AVERAGE THE 00Z NAM IS SLOW WITH THIS FEATURE AS IT APPROACHES THE PACIFIC NORTHWEST COAST LATE TUE NIGHT...WHILE THE 00Z GFS IS ON THE FASTER SIDE OF THE GUIDANCE SOLUTION ENVELOPE. THE 00Z UKMET SPED UP ITS TIMING WITH THE SHORT WAVE...AS HAS THE 00Z CMC. THE 00Z ECMWF ALSO SPED UP ITS SOLUTION...AND FOR NOW THE FASTER SOLUTION IS PREFERRED GIVEN THE FAST LOW AMPLITUDE FLOW. FOR NOW...A BLEND OF THE 00Z ECMWF/GFS IS PREFERRED. HOWEVER...THERE IS STILL ENOUGH SPREAD IN THE GUIDANCE FOR CONFIDENCE TO BE BELOW AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... HAYES