MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 252 PM EDT TUE AUG 04 2015 VALID AUG 04/1200 UTC THRU AUG 08/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION WITH FINAL MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO DEGRADE THEIR SHORT RANGE FORECASTS. CLOSED LOW APPROACHING CA THU NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE REMAINS IN GOOD AGREEMENT WITH THIS SYSTEM. POSSIBLE CLOSED LOW MOVING ALONG WESTERN US/CAN BORDER ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NAM/ECMWF COMPROMISE CONFIDENCE: AVERAGE THE GUIDANCE SHOWS CONSIDERABLE SPREAD WITH THIS SYSTEM. THE SYSTEM IS MOVING OVER THE TOP OF A SOUTHERN STREAM RIDGE WOULD TEND TO ARGUE FOR A FASTER SOLUTION...WHILE THE IDEA THAT IT IS MOVING WITHIN THE SOUTHWEST PORTION OF AN OMEGA-TYPE BLOCK ACROSS CANADA ARGUES FOR A SLOWER SOLN. THE INTERMEDIATE GUIDANCE HERE OF THE 12Z ECMWF/NAM SPLIT THE DIFFERENCE AND A COMPROMISE OF THE TWO IS PREFERRED WITH AVERAGE CONFIDENCE. NORTHERN STREAM SHORTWAVES CROSSING THE DAKOTAS/MN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON NAM/NON UKMET COMPROMISE CONFIDENCE: AVERAGE THE 12Z UKMET BECAME EVEN MORE OUT OF SYNC WITH OTHER MODELS...NOW SHOWING A RIDGE WHERE MOST OF THE OTHER MODELS SHOW A TROF BY 06/18Z. THE NAM APPEARED TO BE OVERLY DEEP. REMOVING THOSE TWO LOOKS LIKE IT SHOULD YIELD A REASONABLE COMPROMISE WITH AVERAGE CONFIDENCE. SHORTWAVE CROSSING THE MID-SOUTH/SOUTHEAST WED/THU ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF COMPROMISE CONFIDENCE: AVERAGE EVEN THOUGH THE GUIDANCE HAS TRENDED NOTICEABLY WEAKER WITH THIS SYSTEM SINCE MONDAY...THE MASS FIELDS STILL HAVE A FAIRLY LARGE SPREAD. THE 12Z CANADIAN REMAINED A STRONG OUTLIER WHICH IS TYPICAL BIAS. A COMPROMISE OF THE 12Z GFS/ECMWF LOOKS REASONABLE HERE AND LEAVES THE STRONGER NAM ON THE EDGE OF MODEL SOLNS. LOW PRESSURE MOVING FROM GA COAST TO THE CAROLINA COAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GFS/NAM COMPROMISE CONFIDENCE: AVERAGE THE SYSTEM LOOKED BETTER IN TERMS OF CONVECTION AND THE FACT THAT THE CIRCULATION HAD BECOME BETTER DEFINED AT ABOUT THE TIME OF A CONVECTIVE BURST EARLIER THIS MORNING. SINCE THEN THE SYSTEM HAS AN ELONGATED/SHEARED APPEARANCE. SO WILL ONCE AGAIN GIVE LEAST CONSIDERATION TO THE STRONGER CANADIAN AS THE SYSTEM PULLS EAST AND MERGES WITH A FRONTAL SYSTEM. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BANN