MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 237 PM EDT SAT AUG 30 2014 VALID AUG 30/1200 UTC THRU SEP 03/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z CMC/UKMET/ECMWF ALONG WITH FINAL PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...UPPER-LEVEL ENERGY LIFTING FROM THE LOWER MS VALLEY UP TOWARD THE OH VALLEY... FINAL PREFERENCE: 12Z GFS/ECMWF/CMC ARE USEFUL FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN UPPER LOW WHICH IS ALONG THE WESTERN GULF COAST HAS BEEN RESPONSIBLE FOR VERY HEAVY RAINFALL THIS MORNING ACROSS LA. AS THE SYSTEM LIFTS NORTH AND EAST...IT WILL GRADUALLY SHEAR AS IT MOVES THROUGH THE TN VALLEY AND EVENTUALLY INTO THE CENTRAL APPALACHIANS. IT APPEARS SOME ENERGY WILL LINGER BACK ALONG THE WESTERN GULF COAST WHILE IN MORE OF A SHEARED STATE. OVERALL...THE 12Z NAM/UKMET SHOW TWO DISTINCT WAVES MOVING THROUGH THE CENTRAL APPALACHIANS/MID-ATLANTIC WHILE THE 12Z GFS/ECMWF/CMC FOCUS ON ONE SHORTWAVE. FEEL MORE COMFORTABLE LEANING ON THIS LATTER CLUSTERING AS THEY FIT MORE REASONABLY WITH THE ENSEMBLE MEANS. ...SHORTWAVE MIGRATING FROM THE UPPER MS VALLEY TO NORTHERN NEW ENGLAND... FINAL PREFERENCE: A NON-12Z UKMET MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE NORTHERN STREAM ENERGY MOVING THROUGH THE UPPER MS VALLEY WILL QUICKLY MOVE THROUGH THE GREAT LAKES AND EVENTUALLY INTO NORTHERN NEW ENGLAND. AFTER EVALUATING ALL OF THE 12Z GUIDANCE...THE MODELS ARE BETTER CLUSTERED THAN EARLIER WITH ONLY THE 12Z UKMET DEPARTING FROM THE GROUPING WITH A SLIGHTLY FASTER SOLUTION. ...LONGWAVE TROF SETTING UP ACROSS THE WESTERN TO CENTRAL U.S... ...ADVANCING COLD FRONT... FINAL PREFERENCE: BLEND OF THE 12Z ECMWF WITH THE 12Z GEFS/00Z ECMWF ENSEMBLE MEANS FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE THE PATTERN BECOMES MORE PROGRESSIVE DURING THIS HOLIDAY WEEKEND AS HEIGHT FALLS TRANSLATE FROM THE NORTHWESTERN U.S. TOWARD THE MIDDLE OF THE COUNTRY. DURING THE INITIAL 24 HOURS OF THE PERIOD...THERE IS SYNOPTIC AGREEMENT AMONG THE MODELS WHILE DIFFERING WITH THE SHORTWAVE DETAILS. BY DAY 2...THE 12Z NAM BECOMES SLOWER WITH THE PROGRESSION OF THE NORTHERN EXTENT OF THE LONGWAVE TROF. MEANWHILE...THE 12Z ECMWF HAS DEFINITELY BACKED OFF ON THE AMOUNT OF AMPLIFICATION OCCURRING ALONG THE WESTERN EDGE OF THE LONGWAVE TROF RELATIVE TO ITS 00Z CYCLE. DIFFERENCES BECOME RATHER LARGE WITH THE POSITION OF THE SURFACE LOW(S) ACROSS ONTARIO. WILL LEAN A LITTLE MORE HEAVILY ON THE ENSEMBLE MEANS GIVEN THE GROWING SPREAD BUT INCORPORATE PORTIONS OF THE 12Z ECMWF SOLUTION AS IT FITS THEM MOST CLOSELY. ...AMPLIFYING SHORTWAVE NEARING THE PACIFIC NORTHWEST BY TUESDAY AFTERNOON... FINAL PREFERENCE: BLEND OF THE 12Z ECMWF/UKMET WITH THE 00Z ECMWF ENSEMBLE MEAN FORECAST CONFIDENCE: SLIGHTLY BELOW AVERAGE AS A LONGWAVE TROF EXTENDS FROM THE EASTERN PACIFIC INTO THE GREAT LAKES REGION...ANOTHER AMPLIFIED SHORTWAVE WILL DIVE TOWARD THE PACIFIC NORTHWEST BY EARLY/MID NEXT WEEK. THERE IS A TREND TOWARD A SLIGHTLY FASTER SOLUTION WHICH INCLUDES THE 12Z ECMWF/CMC/UKMET. THIS NOW LEAVES THE 12Z NAM/GFS BEING SLOWER OVERALL. THIS RUN OF THE 12Z GFS LOOKS A LITTLE OFF AS IT IS DECIDEDLY SLOWER THAN ITS OWN MEAN WITH THE 12Z GEFS MEAN NOW BEING THE FATEST SOLUTION. WILL LEAN ON THE AFOREMENTIONED BUILDING CLUSTER AMONG THE 12Z ECMWF/CMC/UKMET WITH MORE FOCUS ON THE 12Z ECMWF/UKMET GIVEN PREFER THEIR HANDLING WITH THE DOWNSTREAM PORTION OF THE TROF. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER