MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 250 AM EDT SAT JUN 20 2015 VALID JUN 20/0000 UTC THRU JUN 23/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... FINAL 00Z MODEL EVALUATION AND PREFERENCES NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR FORECASTS. ...TROPICAL DEPRESSION BILL... PREFERENCE: GFS/ECMWF/NAM BLEND CONFIDENCE: ABOVE AVERAGE THE GUIDANCE IS IN ALMOST COMPLETE AGREEMENT ON WHAT IS LEFT OF BILL OVER THE NEXT 48 TO 60 HRS. THE MID-LEVEL LOW NEAR SDF SAT MORNING SHEARS OUT TOWARD WV BY SAT EVENING AND THE DELMARVA BY SUN MORNING BEFORE BEING OFFSHORE OF SOUTHERN NEW ENGLAND ON SUN EVENING. THE SURFACE REFLECTION TRACKS FROM EVV/SDF SAT MORNING TO HTS BY SAT EVENING AND JUMP TO JUST EAST OF DC/BAL BY SUN MORNING BEFORE CLIPPING SOUTHERN NEW ENGLAND AND REACHING OFFSHORE OF NOVA SCOTIA... SUN EVENING AND MON MORNING RESPECTIVELY. THROUGH THE FIRST 48 HRS... THE LATEST GFS... NAM AND ECMWF ARE EXTREMELY SIMILAR AND FOR THE MOST PART THIS INCLUDES THE POTENTIAL QPF/HEAVY RAINFALL. THUS WPC WILL RECOMMEND A BLEND OF THESE THREE AND FOR THE LATEST SPECIFIC DETAILS ON BILL...PLEASE REFER TO THE LATEST WPC ADVISORY. ...LOW PRESSURE SYSTEM MOVING FROM THE CENTRAL/NORTHERN PLAINS TO GREAT LAKES AND NORTHERN NEW ENGLAND SUN-MON... PREFERENCE: GFS/ECMWF BLEND CONFIDENCE: ABOVE AVERAGE PROGRESSIVE UPPER-LEVEL WESTERLIES ACROSS THE NORTHERN TIER OF THE COUNTRY WITH AN ARRAY OF UPPER DYNAMICS IS TRIGGERING CLUSTERS OF CONVECTIVE HEAVY RAINS OVER THE UPPER MIDWEST THIS EVENING. THIS WILL RESULT IN A SURFACE WAVE/LOW DEVELOPING OVER SERN SD/NERN NE BY SAT MORNING AND THIS SYSTEM WILL TRANSITION DOWNSTREAM RATHER RAPIDLY. THE LOW WILL TRACK INTO IA BEFORE REACHING LOWER MI BY SUN MORNING... BEFORE REACHING NRN NEW ENGLAND MON MORNING. THE GFS AND ECMWF ARE IDENTICAL THROUGHOUT THIS PROCESS OVER THE NEXT 2 DAYS BEFORE BOTH SOLUTIONS ALLOW THE UPPER DYNAMICS TO MESH WITH REMNANTS OF BILL OFFSHORE OF THE CANADIAN MARITIMES MON INTO TUES. THUS WPC WILL FOLLOW A BLEND OF THIS DUO.. ...UPPER-LEVEL TROUGH MOVING INTO THE PACIFIC NORTHWEST ON SUNDAY/MON... PREFERENCE: COMPROMISE OF GUIDANCE CONFIDENCE: AVERAGE THE DEPARTURE OF THE UPPER LOW FROM BRITISH COLUMBIA WILL RESULT IN SHORT WAVE RIDGING ACROSS THE NW BUT ANOTHER PAC SYSTEM WITH A BROAD UPPER TROUGH WILL REACH THE NW ON SUN. THIS SHOULD DRIVE A DECENT THERMAL ZONE INTO THE REGION LATE SUN INTO MON BUT THE CHANCES OF PRECIPITATION WILL BE EXTREMELY MINIMAL. WPC PREFERRED A COMPROMISE OF THE GUIDANCE AND MASS FIELDS. ...UPPER-LEVEL ENERGY MOVING INTO TEXAS FROM MEXICO SATURDAY INTO SUNDAY... PREFERENCE: ECMWF/GEM GLBL BLEND CONFIDENCE: AVERAGE MODELS ARE IN DECENT AGREEMENT ON UPPER-LEVEL VORTICITY MOVING NORTHWARD FROM MEXICO INTO SOUTHERN/CENTRAL TEXAS SATURDAY INTO SUNDAY. THIS VORTICITY WILL GRADUALLY STRETCH OUT TO THE NORTH AND EAST TOWARD THE LOWER MS VALLEY... WHILE SITTING SOUTH AND EAST OF THE FOUR CORNERS UPPER RIDGE. THE GUIDANCE ALL AGREE A SMALL SCALE HEAVY RAIN POTENTIAL IS POSSIBLE ON SAT BUT DIFFER SOME AS IT COMES TO SUN. WPC WILL RECOMMEND A MODEL BLEND ON SAT AND COMPROMISE OF THE DATA ON SUN. ...UPPER LOW OVER BRITISH COLUMBIA BREAKING DOWN AND SHEARING ACROSS UPPER MIDWEST/GREAT LAKES LATE SUN THROUGH MON... PREFERENCE: NAM/GFS BLEND CONFIDENCE: BELOW AVERAGE THE MODEL GUIDANCE ALL INDICATE THE UPPER LOW OVER BRITISH COLUMBIA BREAKING DOWN ON SAT BEFORE THE UPPER DYNAMICS BEGIN TO GET CAUGHT UP IN THE WESTERLIES. THE GREATEST DISCREPANCY IS THE STRENGTH OF THE DYNAMICS SLIDING SOUTH AND EAST TOWARD THE UPPER MIDWEST ON SUN AND REALLY IMPACTS THE SURFACE PATTERN. THE 12Z/19 ECMWF IS THE STRONGEST AND FASTEST SOLUTION... WHILE THE 00Z GFS/ECMWF IS WEAKER AND ALLOWS THE DYNAMICS TO BLEND IN WITH THE WESTERLIES. THUS THE PREVIOUS ECMWF HAS A SURFACE LOW TRACKING ALONG THE US/CANADIAN BORDER INTO ONTARIO... WHILE THE 00Z GFS/NAM/ECMWF PLACE MORE EMPHASIS ON A LOW TRACKING ACROSS SD/NE AND LIFTING NORTH AND EAST THROUGH THE UPPER MS VALLEY TO ONTARIO. AT THIS TIME... WPC WILL PREFER THE LATTER SOLUTION OF THE 00Z GUIDANCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... MUSHER