MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1232 PM EDT FRI AUG 08 2014 VALID AUG 08/1200 UTC THRU AUG 12/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...UPPER TROUGH EXITING NEW ENGLAND EARLY IN THE PERIOD... PREFERENCE: GENERAL MODEL CONSENSUS CONFIDENCE: ABOVE AVERAGE A DEEP UPPER TROUGH WILL CONTINUE TO EXIT THE NORTHEASTERN U.S. TODAY WITH THE ENERGY LIFTING UP INTO NOVA SCOTIA AND NEWFOUNDLAND THROUGH SAT. THE MODELS ARE IN VERY GOOD AGREEMENT WITH THIS SYS AND SO A GENERAL MODEL COMPROMISE WILL BE PREFERRED ATTM. ...SERIES OF MID-LEVEL IMPULSES CROSSING THE OH/TN VALLEYS AND INTO THE MID-ATLANTIC... ...SURFACE LOWS/FRONTAL ZONE IMPACTING THE REGION... PREFERENCE: BLEND OF THE 00Z ECMWF AND 00Z GEM CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS DEPICT A COUPLE OF SHORTWAVE IMPULSES INCLUDING AN MCV TRAVERSING THE OH/TN VLY REGION OVER THE NEXT COUPLE OF DAYS WHILE GRADUALLY MOVING INTO THE SRN MID-ATLANTIC REGION. A COUPLE OF WAVES OF LOW PRESSURE WILL BE GRADUALLY ADVANCING EAST AS WELL ALONG A FRONTAL ZONE DRAPED FROM THE OH VLY SEWD INTO THE SOUTHEAST COASTAL PLAIN. ONE WAVE IS EXPECTED TO MOVE SLOWLY THROUGH THE OH VLY...WITH ANOTHER ONE DEVELOPING OVER THE INTERIOR SOUTHEAST OVER THE WEEKEND. THE 12Z GFS IS A BIT STRONGER THAN THE GLOBAL MODEL CONSENSUS WITH THE WAVE OVER THE OH VLY...WITH THE 12Z NAM AND NON-NCEP SOLNS ALL A TAD WEAKER. OVER THE SOUTHEAST...THE 12Z GFS IS A LITTLE FARTHER NORTH WITH ITS FRONTAL ZONE COMPARED TO THE REMAINING MODELS WHICH ARE REASONABLY WELL CLUSTERED WITH THEIR POSITION. AS MENTIONED...ALL OF THE MODELS SHOW A WAVE OVER THE COASTAL PLAIN...BUT THE LOW CENTER MOVES TO NEAR OR OFFSHORE THE NC/SC COAST BY MON. THE 00Z GEM/00Z ECMWF AND 12Z GFS SUGGEST SOME DEEPENING OF THE LOW CENTER LATE IN THE PERIOD. THE 00Z UKMET AND 12Z NAM ARE FLATTER AND APPEAR GENERALLY TOO FLAT. THEREFORE...BASED ON THE MODEL SPREAD AND OVERALL STRONGER CLUSTERING...WILL PREFER A SOLN TWD THE 00Z ECMWF AND 00Z GEM. ...UPPER LOW SLOWLY TRACKING OUT INTO THE NORTHERN PLAINS... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A WEAK UPPER LOW OVER WY ATTM WILL ADVANCE EAST OUT ACROSS THE NRN PLAINS THROUGH TONIGHT AN EARLY FRI BEFORE THEN DAMPENING OUT. THERE IS FAIRLY GOOD AGREEMENT ON THE LARGER SCALE WITH THE MASS FIELD DETAILS OF THIS SYS...SO WILL PREFER A GENERAL MODEL COMPROMISE TO RESOLVE THE SMALLER SCALE DIFFS. ...SHORTWAVE TROUGH CROSSING SOUTHERN/CENTRAL CANADA... ...ENERGY DIGGING SOUTHEAST INTO THE UPPER MIDWEST/GREAT LAKES BY MON... PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF AND 00Z GEM CONFIDENCE: AVERAGE THE MODELS ARE BEGINNING TO CLUSTER BETTER WITH THE TIMING AND DEPTH OF A SHORTWAVE TROUGH CROSSING PAC NORTHWEST THROUGH TONIGHT AND THEN RACING ENEWD ACROSS SRN CANADA THROUGH SAT BEFORE AMPLIFYING INTO A CLOSED LOW OVER HUDSON BAY BY SUN. ON MON...A PORTION OF THE OVERALL TROUGH AXIS WILL BE SEPARATING AND DIGGING SEWD INTO THE UPR MIDWEST AND GREAT LAKES REGION. MODEL SPREAD IS MINIMAL WITH THE CANADIAN PORTION OF THE UPR TROUGH/CLOSED AND ASSOCD SFC LOW. THERE IS A BIT MORE SPREAD OVER THE UPR MIDWEST/GREAT LAKES REGION. THE 00Z UKMET AND 12Z NAM TEND TO BE A BIT SLOWER WITH THE SHORTWAVE ENERGY DIGGING SEWD...WITH THE 00Z ECMWF/00Z GEM AND 12Z GFS FASTER. THE LATEST GEFS MEAN AND ECENS MEAN FAVOR THE SOMEWHAT MORE FASTER CONSENSUS...AND THIS WILL BE THE PREFERENCE. ...SLOW-MOVING CLOSED LOW ALONG THE CA COAST... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE CONTINUES TO ADVERTISE A SLOW-MOVING UPPER LOW APPROACHING THE CA COAST THIS WEEKEND AND INTO EARLY MONDAY. THE SPREAD REMAINS LOW THROUGH THE PERIOD. WILL PREFER A GENERAL MODEL COMPROMISE AS A RESULT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON