MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 120 PM EDT THU JUL 02 2015 VALID JUL 02/1200 UTC THRU JUL 06/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS MODEL EVALUATION INCLUDING PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO DEGRADE SHORT RANGE FORECASTS. UPPER TROUGH MOVING THROUGH WESTERN CANADA THROUGH SAT/SUN COLD FRONT DROPPING INTO HIGH PLAINS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z NAM/00Z ECMWF ENSEMBLE MEAN/GEFS MEAN CONFIDENCE: AVERAGE ALL MODELS DEVELOP A STRONG UPPER LOW ACROSS THE NORTHERN CANADIAN PROVIDENCES...WITH THE SOUTHERN PORTIONS AFFECTING THE NORTHERN ROCKIES AND HIGH PLAINS BY SAT INTO SUN. AT THE SURFACE A STRONG LOW ACROSS CANADA WILL DROP A COLD FRONT INTO A LEE CYCLONE THAT WILL DROP ALONG THE FLANKS OF THE ROCKIES FROM EASTERN MONTANA ON SAT TO E COLORADO BY SUN. STRENGTH AND TIMING SEEM TO BE THE MAJOR DIFFERENCES WITH THE MASS FIELDS. THE 00Z CMC IS STRONG AND SLOWEST OF THE GLOBAL MODELS. THE 00Z ECMWF IS MUCH STRONGER THAN OTHER GUIDANCE THOUGH ARE IN FAIRLY GOOD AGREEMENT WITH THE PLACEMENT OF THE UPPER LOW LIKE THE 12Z GFS/NAM AND UKMET. TIMING ISSUES WITH THE BASE OF THE TROF LEAD TO THE DIFFERENCES IN THE SPEED OF THE FRONT. THE 12Z GFS IS THE FASTEST WITH THE FURTHEST SOUTH LEE-CYCLONE POSITION BY THE END OF DAY 3...THE 00Z ECMWF DUE TO ITS OVER DEEPENING ALOFT IS THE SLOWEST AND HAS A STRONGER SURFACE LEE-CYCLONE ACROSS THE BLACK HILLS BY DAY 3 THAN MIDDLE GROUND GUIDANCE. THE 12Z NAM AND 00Z UKMET SPLIT THE DIFFERENCE AND ARE SUPPORTED BY THE 00Z ECMWF MEAN AND 00Z GEFS MEAN. THOUGH THE MASS FIELDS MAY BE A BIT OUT OF SORT...THE AFFECTS TO SENSIBLE WEATHER AND QPF DO NOT APPEAR TOO DRAMATIC AT THIS TIME. A BLEND OF THE 12Z NAM/00Z UKMET WITH 00Z ECMWF MEAN FITS THIS MIDDLE GROUND WELL AND IS PREFERRED AT AVERAGE CONFIDENCE. SURFACE WAVE MOVING EAST FROM KS TO THE MID-ATLANTIC THROUGH SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 00Z GFS AND 00Z ECMWF CONFIDENCE: AVERAGE A MID LEVEL SHORTWAVE TROUGH CURRENTLY OVER MID MISSOURI RIVER VALLEY SHOULD PROGRESS INTO THE LOWER OHIO VALLEY THURS NIGHT AND THE CENTRAL APPALACHIANS FRI NIGHT. THERE IS CONTINUED INCREASING AGREEMENT WITH THE GLOBAL MODELS WITH THE ENSEMBLE RUNS WITH THE EVOLUTION OF THE THE SHORTWAVE TROF AND SURFACE LOW TRACKING FROM KANSAS TO THE APPALACHIANS EVENTUALLY TRANSFERRING TO A LEE-LOW ACROSS THE CAROLINAS BY FRI AND MOVING OFFSHORE BY SAT. THERE IS VERY GOOD LATITUDINAL PACKING OF THE LOCATION/TRACK OF THE SURFACE LOW BUT EASTWARD TIMING IS STILL A BIT DIFFERENT IN THE ENSEMBLE CLUSTER. THE 00Z UKMET HAS GOTTEN BETTER BUT REMAINS FAST TO THE OVERALL SOLUTION. THE 12Z NAM IS A BIT SLOWER LIKELY IN RESPONSE TO SOME INTERACTION WITH UPSTREAM SHORTWAVE ENERGY THAT APPEARS TOO STRONG AT THIS TIME (SEE BELOW). THE 12Z GFS CONTINUES GOOD AGREEMENT WITH 00Z ECMWF AND ARE GOOD REPRESENTATIONS OF THE MEAN WITH LOW. AS SUCH A BLEND OF THE 12Z GFS AND 00Z ECMWF WILL BE PREFERRED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. SHORTWAVE CLIPPING THE NORTHERN GREAT LAKES FRI/SAT...AND NORTHERN NEW ENGLAND BY SUN ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z NAM/GFS/00Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE FAIRLY GOOD AGREEMENT EXISTS WITH THE SHORTWAVE AND ASSOCIATED LOW THAT TRAVERSES THE PERIPHERY OF HUDSON AND JAMES BAY CLIPPING THE WESTERN GREAT LAKES WITH AFFECTS ON LATE FRI INTO SAT. THE 00Z CMC BEING A BIT SLOWER THAN THE WELL PACKED CLUSTER OF SURFACE LOWS IN EASTERN ONTARIO...AND CONTINUES SLOW THROUGH THE REST OF THE TIME PERIOD. AS THE SYSTEM PROGRESSES EAST...PHASING WITH SOUTHERN STREAM ENERGY ALLOWS THE 00Z UKMET TO DIVERGE FROM THE REST OF THE GROUP...BECOMING FAST AND STRONG ALOFT. OTHERWISE GOOD AGREEMENT WITH THE 12Z NAM/GFS ALONG WITH THE 00Z ECMWF ALLOWS A BLEND OF ALL THREE WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE. WEAK SHORTWAVE ENERGY ENTERING BASE OF EASTERN US TROF AS THE LARGE SCALE TROF LIFTS TOWARD NORTHEAST BY MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF 00Z ECMWF/ECMWF ENSEMBLE MEAN/12Z GFS CONFIDENCE: SLIGHTLY BELOW AVERAGE WEAK SHORTWAVE ENERGY EXITING THE SOUTHERN CANADIAN ROCKIES INTO THE BASE 0F THE EASTERN U.S. TROF THROUGH THE WEEKEND. MODELS DIFFER IN STRENGTH OF THE WAVE WITH SIGNIFICANT SPREAD IN ENSEMBLE SOLUTIONS ACROSS THE EASTERN THIRD OF THE U.S BY SUNDAY NIGHT. THOUGH WITH THE OVERALL TROF FILLING/LIFTING NORTHEAST...DIFFERENCES ARE REFLECTED BEST BY QPF FIELDS. THE 12Z NAM IS THE MOST AGGRESSIVE AND STRONG WITH THE WAVE WITH SOME SUPPORT FROM THE 00Z UKMET AND 00Z CMC. THE 00Z ECMWF HAS SOME OF THIS ENERGY BUT MORE STUNG OUT IN A STRING OF SMALLER VORT CELLS THAN A MORE CONSOLIDATED LOW. THE 12Z GFS IS THE SLOWEST AND WEAKEST BARELY RESOLVING ANY ENERGY WITH THE SHORTWAVE. GIVEN THE LARGE SPREAD BY DAY 3...A WEAKER FLATTER SOLUTION IS PREFERRED AT THIS TIME THOUGH WITH SLIGHTLY BELOW AVERAGE CONFIDENCE...AS SUCH A BLEND OF THE 00Z ECMWF/12Z GFS AND ECMWF ENSEMBLE MEAN BEST REPRESENTS THE MIDDLE GROUND AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA