MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1255 AM EDT THU JUL 30 2015 VALID JUL 30/0000 UTC THRU AUG 02/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NCEP MODEL EVALUATION WITH ANALYSIS AND INITIAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ANY NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO AFFECT SHORT TERM FORECAST ERRORS WELL DEFINED UPPER LOW ACROSS WESTERN ONTARIO SETS UP OVER HUDSON BAY BY FRIDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS/NAM AND 12Z ECMWF CONSENSUS CONFIDENCE: ABOVE AVERAGE OVERALL MODEL AGREEMENT WAS GOOD WITH RESPECT TO THE STRENGTH/TIMING OF THE UPPER LOW AND SURFACE COLD FRONT MOVING EAST ACROSS THE REGION. LOW-LEVEL SHEAR AXIS WITH EMBEDDED WEAK SURFACE LOWS ACROSS THE GULF OF MEXICO ASSOCIATED WEAK UPPER LOW/ELONGATED TROF ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL NCEP/ECMWF DETERMINISTIC MODEL CONSENSUS CONFIDENCE: BELOW AVERAGE MODELS START OFF IN GOOD AGREEMENT WITH THE TROUGH AXIS AND GENERAL CORRIDOR OF VORTICITY MAXIMA THURSDAY INTO THE DAY ON FRIDAY. SPREAD AMONG THE GUIDANCE EMERGES BY LATE FRIDAY AND BECOMES GREATER SATURDAY INTO EARLY SUNDAY. AS MENTIONED IN THE PREVIOUS DISCUSSION...MODELS DIVERGE ON WHICH VORT AREAS BECOME DOMINANT AND HOW MUCH OF THE ENERGY IS PUSHED NORTHEAST WITH THE LONG WAVE UPPER TROUGH OVER THE EAST COAST...AND HOW MUCH IS LEFT BEHIND TO PROGRESS WEST INTO THE GULF OF MEXICO. IN THE BROADEST SENSE...THE 00Z NCEP MODEL RUNS STAYED WITH THE IDEA THAT MORE OF THE SHORTWAVE ENERGY WOULD BE OFF THE EAST COAST OF FL AND PULLING TOWARDS THE EAST WHILE LEAVING LESSER AMOUNTS OF ENERGY OVER THE GULF OF MEXICO. THIS IDEA HAD THE SUPPORT OF THE 29/12Z ECMWF WHILE THE 29/12Z RUNS OF THE CANADIAN AND UKMET FAVORED KEEPING THE BULK OF THE SHORTWAVE ENERGY OVER THE GULF. ADDITIONAL SHORTWAVE ENERGY OVER BRITISH COLUMBIA ADVANCING INTO THE GREAT LAKES DEEPENING THE LARGE SCALE TROF THU INTO SAT. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ PREFERENCE: 12Z GFS/ECMWF CONFIDENCE: AVERAGE ON THURSDAY EVENING ONE SHORTWAVE IS EXPECTED TO MOVE ACROSS THE GREAT LAKES AND PUSH NORTHEAST INTO NEW ENGLAND ON FRIDAY. ADDITIONAL SHORTWAVE ENERGY WILL DIVE INTO THE GREAT LAKES FRIDAY INTO SATURDAY ACTING TO DEEPEN THE LARGE SCALE TROUGH OVER THE EASTERN PORTION OF THE COUNTRY. WITH THE FIRST SHORTWAVE...THE 00Z GFS AND THE 29/12Z ECMWF SEEM TO HAVE THE BEST HANDLE ON TIMING AND STRENGTH...WHILE THE 00Z NAM AND THE 29/12Z UKMET WERE TOO SLOW AND FAST RESPECTIVELY. THE MOST RECENT RUN OF THE ENSEMBLES LEND SUPPORT TO THE GFS/ECMWF. AS THE SHORTWAVE ENERGY MOVES INTO THE GREAT LAKES REGION...THE 00Z NAM AND THE UKMET WERE SHARP OUTLIERS. IN THE CASE OF THE UKMET...IT OUTRAN OTHER GUIDANCE AND ENSEMBLE MEANS BY DAY 3. THINK THE GFS/ECMWF COMBINATION IS THE BEST BET AT THIS POINT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BANN