MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 304 PM EDT FRI JUL 03 2015 VALID JUL 03/1200 UTC THRU JUL 07/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM/GFS WITH FINAL PREFERENCE AND CONFIDENCE ...UPPER TROUGH MOVING THROUGH WESTERN/CENTRAL CANADA THROUGH SAT AND SUN... ...COLD FRONT CROSSING THE NORTHERN PLAINS/UPPER MS VALLEY... PREFERENCE: 12Z GFS/NAM/ECMWF CONFIDENCE: AVERAGE THE 12Z NAM IS WITHIN THE SPREAD OF SOLUTIONS ACROSS CENTRAL CANADA DURING DAY 1 INTO DAY 2...BUT BECOMES SLOWER AND DEEPER WITH TIME ACROSS THE NORTHERN PLAINS DURING DAY 3. THE CORRESPONDING SURFACE FRONT IS SLOW AS WELL...ESPECIALLY BY DAY 3 ACROSS THE GREAT LAKES. THE 12Z ECMWF HAS TRENDED AWAY FROM ITS SOLUTION BECOMING MUCH FASTER ACROSS CANADA BUT RETAINING MORE ENERGY TO INCREASE THE POSITIVE TILT OF THE TROF ACROSS WESTERN CANADA INTO MONTANA BY MONDAY...SO MUCH SO THAT IT IS NOW TRENDING SLOWER IN THE BASE OF THE TROF THAN THE 12Z NAM/GFS/CMC. AT THE SURFACE...TIMING OF THE COLD FRONT PROGRESSING ACROSS THE NORTHERN PLAINS INTO THE CENTRAL PLAINS SEEMS TO BE LINED UP QUITE WELL WHICH INCREASES CONFIDENCE IN A GENERAL BLEND OF THE 12Z GLOBAL MODELS. HOWEVER...DIFFERENCES OCCUR IN THE PLACEMENT OF THE SURFACE WAVES THAT DEVELOP ALONG THE LEE OF THE ROCKIES AND LIFT ALONG THE FRONT AS IT PROGRESSES EAST. THIS LEADS TO DECENT SPREAD IN THE SURFACE MASS/WIND FIELDS TO REDUCE CONFIDENCE IN AN OVERALL BLEND WASHING OUT THESE WAVES. LARGE DIFFERENCES IN THE LOCATION/EVOLUTION OF THE DEEP OCCLUDED LOW ACROSS CENTRAL CANADA WITH THE 12Z UKMET/CMC ENOUGH TO ELIMINATE THEM FROM A LARGE BLEND OF 12Z GFS/NAM/ECMWF IN THE PREFERENCE. BLENDING ALL THESE SOLUTIONS WITH DECENT ENOUGH SPREAD REDUCES CONFIDENCE IN THE PREFERRED BLEND TO AVERAGE. ...SURFACE WAVE MOVING THROUGH THE OH VALLEY AND MID-ATLANTIC THROUGH SAT... PREFERENCE: NON-CMC CONSENSUS CONFIDENCE: ABOVE AVERAGE THE 12Z NAM SLOWS DURING THE LATER STAGES OF DAY 1 ACROSS THE MID ATLANTIC WITH THE MID LEVEL SHORT WAVE...AND ITS ASSOCIATED SURFACE FRONT ALSO SLOWS WITH RESPECT TO THE CONSENSUS. THE 12Z GFS IS IN THE MIDDLE OF THE CONSENSUS WITH THE MID LEVEL SYSTEM. THE SURFACE LOW...WHILE A TAD SLOW EARLY...CATCHES UP TO THE CONSENSUS BY THE END OF DAY 1...AND REMAINS THERE INTO DAY 2. THE 12Z CMC SPLITS THE SURFACE SOLUTION WITH A MID-ATLANTIC LOW THAT IS IN GOOD AGREEMENT THOUGH A BIT FASTER THAN THE OTHER OPERATIONAL MODELS. IT ALSO RETAINS A WEAK LOW ACROSS CENTRAL KENTUCKY WHICH LAGS THE CONSENSUS AS WELL. AS SUCH A NON-CMC BLEND IS PREFERRED WITH ABOVE AVERAGE CONFIDENCE GIVEN THE RUN TO RUN CONSISTENCY AND CLOSE CLUSTERING OF THE REMAINING MODEL SOLUTIONS WITH STRONG ENSEMBLE SUPPORT. ...SHORTWAVE CLIPPING THE GREAT LAKES/NORTHERN NEW ENGLAND THROUGH SUN... PREFERENCE: 12Z GFS/*00Z* ECMWF CONFIDENCE: AVERAGE THE 12Z NAM IS SLOWER AND DEEPER THAN THE CONSENSUS WITH THE TROUGH ACROSS NEW ENGLAND DURING DAY 1. THE 12Z GFS HAS SPED UP ITS SOLUTION AND IS NOW VERY CLOSE TO THE 00Z ECMWF SOLUTION. THE 12Z CMC IS A BIT WEAKER WITH THIS FEATURE...WHILE THE 12Z UKMET LOOKS REASONABLE AT THE SURFACE...THE TROF ALOFT IS MUCH DEEPER AND SLOWER THAN PREFERRED. THE 12Z ECMWF HAS TRENDED FASTER MUCH IN LINE WITH THE 12Z CMC LIKELY TRANSFERRING A BIT OF ENERGY TOWARD DEVELOPING THE COASTAL SURFACE LOW THAT EJECTS OUT OF THE MID-ATLANTIC. THIS LEAVES THE SURFACE REFLECTION MUCH WEAKER THAN THE 00Z RUN AND DIFFERENT FROM ENSEMBLE SUPPORT. IN AN ATTEMPT TO MITIGATE SOME OF THE DIFFERENCES...A BLEND OF THE 12Z GFS/*00Z* ECMWF SOLUTION IS PREFERRED WITH SUPPORT FROM ENSEMBLE MEANS... HOWEVER ENOUGH SPREAD STILL EXISTS PARTICULARLY OVER NEW ENGLAND ON DAY 2 (SUN) TO KEEP AVERAGE CONFIDENCE AT THIS TIME. ...UPPER TROUGH CROSSING THE GULF COAST STATES/SOUTHEAST SUN AND MON... PREFERENCE: 12Z ECMWF CONFIDENCE: BELOW AVERAGE THE 12Z NAM IS SLOWER AND DEEPER WITH THE CROSSING THE GULF COAST STATES ON DAY 1...AND REMAINS SLOWER AND DEEPER THAN THE CONSENSUS THROUGH DAYS 2 AND 3. THE 12Z GFS IS CLOSER TO THE CONSENSUS ON DAY 1...BUT BECOMES SLOWER AND DEEPER WITH TIME (EVENTUALLY BECOMING SLOWER THAN THE 12Z NAM) AS A BIT OF WEAK ENERGY DROPS DOWN INTO THE BASE OF THE TROF TO RELOAD IT WHILE OTHER GUIDANCE DOES NOT RESOLVE THE STRENGTH OF THIS ENERGY AS MUCH...MAKING IT A BIT LESS PREFERRED AT THIS TIME. THE 12Z UKMET CONTINUES TREND OF RESOLVING AN OVERALL WEAK TROUGH. THE STRONGER MODEL CLUSTERING INVOLVES THE 12Z CMC AND THE 12Z ECMWF...HOWEVER...SOME CONVECTIVE FEEDBACK IN SOME OF THE QPF FIELDS PARTICULARLY OVER EASTERN TN AND KY ON SUNDAY BRINGING IT INTO QUESTION. AS SUCH THE PREFERENCE IS THE 12Z ECMWF WHICH IS THE MOST CENTRAL OF THE SOLUTIONS AND HAS SUPPORT FROM THE SREF AND ECMWF ENSEMBLE MEANS. THOUGH GIVEN THE LARGE SPREAD STILL TO BE RESOLVED BY DAY 2-3...CONFIDENCE IS BELOW AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... TEAM WPC