MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 248 PM EDT MON JUN 09 2014 VALID JUN 09/1200 UTC THRU JUN 13/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z CMC/UKMET/ECMWF ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... BASED ON 12Z RAOBS...THE 12Z NAM/GFS ARE TOO AGGRESSIVE WITH PWATS ACROSS CENTRAL TX WHILE BEING UNDERDONE IN WEST TX. BOTH CONTAIN DIFFERENCES ON THE ORDER OF 0.25 INCHES OR SO. ...SLOW-MOVING CLOSED LOW INITIALLY OVER THE CENTRAL PLAINS REACHING THE OH/TN VALLEY BY 12/1200Z... FINAL PREFERENCE: BLEND OF THE 12Z GFS/ECMWF FORECAST CONFIDENCE: AVERAGE CURRENT WATER VAPOR/SATELLITE IMAGERY SHOW A WELL-DEFINED UPPER LOW SPINNING ACROSS THE CENTRAL HIGH PLAINS. MODELS SHOWS THIS FEATURE WOBBLING SLOWLY TOWARD THE SOUTH AND EAST WHILE BEING WELL SEPARATED FROM THE ACTIVE/MORE PROGRESSIVE NORTHERN BRANCH OF THE JET. BY 10/1200Z...THE GUIDANCE IS NEARLY UNANIMOUS IN BRINGING THE SYSTEM TO THE AR/OK/MO BORDER. AHEAD OF A BUILDING EAST COAST/WESTERN ATLANTIC RIDGE...THE UPPER LOW SHOULD SLOWLY BEGIN TO GAIN LATITUDE WHILE TRACKING TOWARD THE OH RIVER VALLEY. THE MID-LEVEL VORTICITY MAY EVEN SPLIT WITH THE NORTHERN BATCH LIFTING INTO THE LOWER GREAT LAKES WHILE THE OTHER ENERGY DROPS INTO THE SOUTHEASTERN U.S. DIFFERENCES ARE A LITTLE MORE OBVIOUS AT THE SURFACE WITH REGARD TO HOW QUICKLY THE SURFACE LOWS SLIDE EASTWARD IN TIME. ENSEMBLE SURFACE LOW PLOTS SHOW QUITE A BIT OF SPREAD WITH MORE OF THE 00Z ECMWF ENSEMBLE MEMBERS SUPPORTING A MORE WESTERN SOLUTION WHILE THE 00Z GEFS MEMBERS ARE JUST OFF TO THE EAST. WITH THE 12Z ECMWF CONTINUING TO FAVOR SOLUTIONS CLOSE TO THE CENTER WHICH INCLUDES THE 12Z GFS AND 12Z GEFS/09Z SREF MEANS...FEEL COMFORTABLE MAINTAINING THE PREVIOUS PREFERENCE. ...UPPER LOW OFFSHORE REACHING SOUTHERN CA BY TUESDAY EVENING... FINAL PREFERENCE: NON-12Z NAM MODEL COMPROMISE FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN UPPER LOW CURRENTLY SLIDING TOWARD THE WEST COAST SHOULD MOVE INLAND BY TUESDAY AFTERNOON/EVENING WHILE BECOMING MORE OF AN OPEN WAVE. THE 12Z NAM/CMC ARE A BIT FASTER AS THE SYSTEM PUSHES INTO THE DESERT SOUTHWEST BY MID-WEEK. HOWEVER...THE 12Z CMC EVENTUALLY SLOWS BACK TOWARD THE REST OF THE PACK THEREAFTER. THERE ARE INDICATIONS THIS AREA OF LOW PRESSURE SHOULD BEGIN TO SHEAR WHILE MIGRATING TOWARD THE FOUR CORNERS REGION. EVENTUALLY THIS SYSTEM BECOMES ABSORBED WITH LITTLE INDICATION LEFT IN THE 500-MB HEIGHT FIELDS. OVERALL...WITH THE EXCEPTION OF THE 12Z NAM...THE MODELS ARE IN CLOSE ENOUGH AGREEMENT TO AFFORD A GENERAL MODEL COMPROMISE. THUS...THE RECOMMENDATION IS A NON-12Z NAM MODEL COMPROMISE. ...SERIES OF NORTHERN STREAM SYSTEMS AFFECTING THE PACIFIC NORTHWEST EASTWARD TO THE GREAT LAKES... FINAL PREFERENCE: UPPER MIDWEST TROF: BLEND OF THE 00Z ECMWF/UKMET...PACIFIC NORTHWEST: BLEND OF THE 00Z ECMWF WITH THE 00Z ECMWF ENSEMBLE/06Z GEFS MEANS FORECAST CONFIDENCE: AVERAGE THE NORTHERN BRANCH OF THE JET WILL BE FAIRLY ACTIVE CARRYING A SERIES OF SYSTEMS THROUGH THE PACIFIC NORTHWEST AND EVENTUALLY INTO THE GREAT LAKES. ONE PARTICULAR SHORTWAVE WILL DRIVE A WELL-DEFINED SURFACE LOW THROUGH THE NORTHERN PLAINS/UPPER MIDWEST ON WEDNESDAY WITH THE 12Z GFS LOOKING MORE LIKE A LOWER PROBABILITY SOLUTION RIGHT NOW. THE 12Z GFS IS FLATTER AND DOES NOT CARRY MUCH LOW PRESSURE TOWARD THE CANADIAN BORDER. PREFER THE 12Z ECMWF/UKMET HERE ALTHOUGH THEY DO EXUDE SOME DIFFERENCES IN TIMING WITH THE FORMER MODEL BEING A BIT QUICKER. FURTHER UPSTREAM...ANOTHER STRONG UPPER TROF SHOULD DESCEND UPON THE PACIFIC NORTHWEST BY EARLY THURSDAY. THE 12Z NAM IS THE MOST PROGRESSIVE SOLUTION WHILE THE 12Z CMC IS QUITE A BIT SLOWER THAN OTHER MODELS. CONSERVATIVELY WILL RECOMMEND A MIX OF THE 12Z ECMWF/UKMET WITH THE 00Z ECMWF ENSEMBLE MEAN. ...SHORTWAVE INTENSIFYING IN THE VICINITY OF THE OK/KS BORDER LATE IN THE PERIOD... FINAL PREFERENCE: BLEND OF THE 12Z GFS/ECMWF/UKMET FORECAST CONFIDENCE: BELOW AVERAGE TOWARD THE END OF THE PERIOD...MODELS DEPICT DEVELOPMENT ALONG THE FRONT RANGE OF THE ROCKIES WITH A FAIRLY POTENT SHORTWAVE MOVING OFF INTO THE CENTRAL HIGH PLAINS BY EARLY THURSDAY. PRESUMABLY THE MODELS ARE FORECASTING SOME SORT OF MESOSCALE COMPLEX SLIDING THROUGH THE LOWER CENTRAL PLAINS EARLY THURSDAY MORNING WITH THE GUIDANCE DISAGREEING ON TIMING/EVOLUTION. THE BIGGEST OUTLIERS AT THIS POINT ARE THE 12Z NAM/CMC WHICH ARE WELL TO THE SOUTHEAST OF THE BETTER CLUSTERING. ENSEMBLE MEANS WOULD BEST FAVOR SOME COMBINATION OF THE 12Z GFS/ECMWF/UKMET. WILL STICK WITH THIS IDEA BUT CONFIDENCE IS BELOW AVERAGE GIVEN THE COMPLEX NATURE OF FORECASTING A MESOSCALE SYSTEM 3 DAYS OUT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER