MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 101 PM EDT SAT JUL 11 2015 VALID JUL 11/1200 UTC THRU JUL 15/0000 UTC ..SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...SHORTWAVE CROSSING THE NC OUTER BANKS BY THIS EVENING... ...SURFACE LOW DEVELOPMENT OFF THE NC COAST... PRELIMINARY PREFERENCE: BLEND OF THE 12Z NAM/00Z ECMWF FORECAST CONFIDENCE: AVERAGE WATER VAPOR IMAGERY SHOWED QUITE A STRONG MID/UPPER LEVEL MOISTURE GRADIENT IN PLACE IN THE PERIPHERY OF THIS SYSTEM. A BAND OF CONVECTION IS CURRENTLY EXITING INTO SOUTHEASTERN VA WITH THE ASSOCIATED HEIGHT FALLS/CONVECTION INDUCING AN AREA OF LOW PRESSURE OFF THE NC COAST BY EARLY SUNDAY MORNING. ALL MODELS AGREE WITH THIS EVOLUTION EXCEPT FOR THE 00Z CMC WHICH IS SLOWER/WEAKER WITH THE MID-LEVEL TROUGH WHICH LEADS TO A MORE SUPPRESSED LOW CENTER. THEREAFTER...MODEL DISAGREEMENT INCREASES REGARDING THE NORTHWARD PUSH OF THIS WAVE ALONG THE WESTERN ATLANTIC. THE 12Z NAM AND 00Z ECMWF/ECMWF ENSEMBLE FAVOR A MORE EASTERN TRACK WHILE THE 12Z GFS/00Z UKMET AND 06Z GEFS/09Z SREF MEANS ARE TO THE WEST. ENSEMBLE LOW PLOTS SHOW MORE SUPPORT FOR THE FORMER CAMP CONTAINING THE NAM/ECMWF SOLUTIONS. WILL FAVOR A SPLIT OF THESE TWO AS THE PREFERENCE. ...LOBE OF VORTICITY TRACKING FROM THE LOWER GREAT LAKES TOWARD NEW ENGLAND THROUGH LATE SUNDAY... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE WITHIN THE SHEARED SOUTHWESTERLY FLOW ACROSS THE NORTHERN ROCKIES/PLAINS REGION...SOME OF THIS SHORTWAVE ENERGY WILL ORGANIZE AND TRACK ACROSS THE LOWER GREAT LAKES ON SUNDAY MORNING. THE 12Z NAM/09Z SREF MEAN ARE SLOWER OUTLIERS WHILE THE 12Z GFS/00Z ECMWF HAVE BETTER ENSEMBLE SUPPORT. THE SIGNAL OF THIS FEATURE BECOMES MORE FUZZY INTO EARLY NEXT WEEK AS THE SYSTEM BEGINS TO SHEAR OUT ACROSS UPSTATE NY. OVERALL...A COMBINATION OF THE 12Z GFS/00Z ECMWF SHOULD SUFFICE HERE. ...AMPLIFIED FLOW RACING FROM THE NORTHERN PLAINS TOWARD THE LOWER GREAT LAKES/OH VALLEY... ...SURFACE BOUNDARY/ASSOCIATED CONVECTION... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: BELOW AVERAGE SHORTWAVE ENERGY CURRENTLY OVER THE INTERMOUNTAIN WEST REGION WILL ACCELERATE NORTH AND EAST ABOVE A BUILDING UPPER RIDGE ACROSS THE SOUTHERN/CENTRAL PLAINS. THESE MID-LEVEL HEIGHT FALLS ARE FORECAST TO RACE SOUTHEASTWARD ABOVE THE RIDGE TOWARD THE GREAT LAKES/OH VALLEY REGION. STRONG FORCING/DYNAMICS WILL THIS SYSTEM SHOULD PROVIDE THE FOCUS FOR A DECENT HEAVY RAINFALL/CONVECTIVE EVENT. THROUGH 14/0000Z...THE 12Z NAM LOOKS LIKE AN OUTLIER ON THE UPSTREAM SIDE OF THIS TROUGH AS IT BREAKS THE NORTHERN PART OF THE RIDGE DOWN WHICH DOES NOT LOOK REASONABLE. THE BIGGEST ISSUES MOVING FORWARD ARE HOW QUICKLY THE HEIGHT FALLS WILL EJECT DOWNSTREAM AND THE LOCATION OF INDIVIDUAL SHORTWAVES WITHIN THIS ENHANCED FLOW REGIME. THE MULTI-DAY TREND IN THE ENSEMBLE SPAGHETTI PLOTS IS TO BE SLOWER. HOWEVER...THE 00Z ECMWF IS PERHAPS TOO SLOW AS IT IS NORTH AND WEST OF ITS ENSEMBLE MEAN. PLAN ON COMPROMISING BETWEEN THE FASTER/SLOWER SOLUTIONS BUT UTILIZING THE 00Z ECMWF ENSEMBLE MEAN OVER THE DETERMINISTIC RUN. WPC FAVORS A BLEND OF THE 12Z GFS WITH THE 00Z ECMWF ENSEMBLE MEAN. CONFIDENCE IS BELOW AVERAGE GIVEN THE COMPLEXITIES OF THE PATTERN. ...MEAN UPPER TROUGH ANCHORING THE WEST COAST... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE THROUGHOUT MUCH OF THE FORECAST PERIOD...A MEAN TROUGH WILL ANCHOR THE WEST COAST AND THE ADJACENT PACIFIC WATERS. THE SPREAD IS NOT TERRIBLY LARGE BUT THERE ARE SOME DIFFERENCES WITH THE POSITION OF THIS TROUGH TOWARD THE END OF THE PERIOD. THE 00Z UKMET IS RIGHT NOW ON THE FASTER SIDE WHILE THE 12Z NAM IS SLIGHTLY WEST OF THE CONSENSUS. AVERAGING OUT THE DIFFERENCES WOULD SUGGEST A BLEND OF THE 12Z GFS/00Z ECMWF IS REASONABLE. ...STRONG UPPER TROUGH AMPLIFYING OVER EASTERN CANADA LATE IN THE PERIOD... PRELIMINARY PREFERENCE: BLEND OF THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: AVERAGE BY EARLY/MID NEXT WEEK...THERE WILL BE QUITE A POTENT UPPER TROUGH AFFECTING THE UPPER REACHES OF THE MAP DOMAIN. THERE APPEARS TO BE ENOUGH VARIABILITY IN THE SOLUTION ENVELOPE TO SUPPORT AN ENSEMBLE APPROACH. AT THIS POINT WILL LEAN ON A BLEND OF THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER