MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1135 AM EST TUE JAN 13 2015 VALID JAN 13/1200 UTC THRU JAN 17/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ...AN EVALUATION OF THE 12Z NAM/GFS ALONG WITH PRELIMINARY PREFERENCES/FORECAST CONFIDENCE... THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE 12Z NAM/GFS DEEMED SIGNIFICANT ENOUGH TO IMPACT THEIR FORECASTS. ...WEAK SHORTWAVE CROSSING THE LOWER MID-ATLANTIC EARLY WEDNESDAY... PRELIMINARY PREFERENCE: A NON-12Z NAM/00Z CMC SOLUTION FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE A SUBTLE REGION OF HEIGHT FALLS MOVING FROM THE ARKLATEX TOWARD THE LOWER MID-ATLANTIC WILL FEATURE A FEW WEAK MID-LEVEL SHORTWAVES. THIS SYSTEM IS FORECAST TO SPREAD PRECIPITATION TO THE CAROLINA COAST EXTENDING NORTHWARD UP TOWARD THE DELMARVA. THE SURFACE REFLECTION SHOWS AN AREA OF LOW PRESSURE DEVELOPING OFF THE CAROLINAS BY 14/1200Z WITH THE 12Z NAM/00Z CMC BEING DISPLACED TO THE NORTH AND WEST RELATIVE TO OTHER GUIDANCE. WILL LEAN ON A NON-12Z NAM/00Z CMC SOLUTION UNLESS OTHER FUTURE MODELS TREND THIS DIRECTION. ...CLOSED LOW MOVING ACROSS THE FOUR CORNERS REGION ON WEDNESDAY MORNING... ...RESULTANT HEIGHT FALLS MIGRATING THROUGH THE SOUTHEASTERN U.S. THURSDAY NIGHT... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF FORECAST CONFIDENCE: AVERAGE WATER VAPOR IMAGERY SHOWS A CLOSED LOW PUSHING ACROSS SOUTHWESTERN UT. THIS BROAD POSITIVELY-TILTED TROF WILL SLIDE SOUTH AND EAST WITH THE SYSTEM BRIEFLY STALLING OVER AZ/NM ON WEDNESDAY MORNING. INITIALLY...THE 00Z CMC/UKMET ARE A TAD WEST OF THE STRONGER CONSENSUS. AS THE UPPER TROF BEGINS TO ACCELERATE EASTWARD...THE 09Z SREF MEAN/06Z GFS-PARALLEL BECOME MORE SLUGGISH BEING MUCH SLOWER IN NATURE. REGARDING OTHER MODELS...THE 12Z GFS/00Z ECMWF SEEM TO BE FOLLOWING THE 00Z ECMWF ENSEMBLE MEAN WHILE THE 12Z NAM AGREES WITH THE 06Z GEFS MEAN. THE SLOWER MODELS EVENTUALLY ATTEMPT TO MAINTAIN A BATCH OF MID-LEVEL VORTICITY ACROSS THE FOUR CORNERS REGION WHILE THE MORE PROGRESSIVE 12Z GFS/00Z ECMWF DO NOT DEPICT THIS. ENSEMBLE SPAGHETTI PLOTS SUGGEST THE SLOWER SOLUTIONS ARE LESS LIKELY SO WILL LEAN TOWARD THE 12Z GFS/00Z ECMWF IDEAS. ...DEEP UPPER TROF SWINGING THROUGH SOUTHEASTERN CANADA BY 16/1200Z... ...PROGRESSIVE FRONTAL BOUNDARY... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS/00Z ECMWF...2/3 TOWARD THE 00Z ECMWF FORECAST CONFIDENCE: AVERAGE THE ACTIVE NORTHERN BRANCH OF THE JET WILL ALLOW A SERIES OF SHORTWAVES TO CROSS THE GREAT LAKES AND SOUTHEASTERN CANADA THROUGHOUT THE PERIOD. THE MOST PRONOUNCED OF THESE IMPULSES IS FORECAST TO CROSS SOUTH OF HUDSON BAY BY 16/0000Z WITH THE 12Z GFS BEING THE MORE AMPLIFIED SOLUTION ALOFT. THIS MORE AMPLIFIED SOLUTION IS ALSO QUICKER WHICH AGREES WITH THE ITS 06Z GEFS MEAN. ON THE OPPOSITE SIDE OF THE SPECTRUM ARE THE 00Z CMC/UKMET WHICH ARE FLATTER ALOFT AND KEEP THE SURFACE WAVE WELL NORTH OF THE INTERNATIONAL BORDER. THE ENSEMBLE LOW PLOTS SHOW PRETTY STRONG CLUSTERING ALONG THE SOUTHERN FRINGE OF THE SPREAD. A MAJORITY OF THE 00Z ECMWF ENSEMBLE MEMBERS SUPPORT THIS NOTION WITH A TREND IN THE SOUTHWARD DIRECTION RELATIVE TO THE 12Z CYCLE YESTERDAY. PLAN ON INCORPORATING SOME OF THE 12Z GFS SOLUTION BUT LEAN MORE HEAVILY ON THE 00Z ECMWF GIVEN THE BELIEF THE GFS MAY BE TOO QUICK. ...INITIAL SHORTWAVE REACHING THE PACIFIC NORTHWEST LATE WEDNESDAY... PRELIMINARY PREFERENCE: MODEL COMPROMISE BETWEEN THE 12Z GFS AND 00Z ECMWF/CMC FORECAST CONFIDENCE: SLIGHTLY ABOVE AVERAGE AN UPPER RIDGE INITIALLY ANCHORING THE EASTERN PACIFIC WILL MOVE EASTWARD AND FLATTEN IN RESPONSE TO HEIGHT FALLS APPROACHING FROM THE WEST. THE 12Z NAM/06Z GFS-PARALLEL LOOK LIKE A FAST OUTLIER AT THE THE START. A PRETTY STRONG CONSENSUS IN FORMED BY THE 12Z GFS AND 00Z ECMWF/CMC SO WILL MAKE THIS COMPROMISE THE PREFERENCE HERE. ...ADDITIONAL PACIFIC ENERGY SLIDING INTO THE PACIFIC NORTHWEST BY 16/0600Z... PRELIMINARY PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF/UKMET FORECAST CONFIDENCE: AVERAGE THE FLOW BECOMES MORE ZONAL LATE IN THE PERIOD WITH ADDITIONAL PACIFIC ENERGY CROSSING THE NORTHWESTERN CORRIDOR OF THE U.S. AS WAS THE CASE WITH THE PREVIOUS PACIFIC SYSTEM...THE 12Z NAM/06Z GFS-PARALLEL ARE OUT OF PHASE WITH THE OTHER GUIDANCE. WHILE THE OTHER MODELS DO EXCUDE SOME SPREAD DOWNSTREAM WHILE PUSHING THROUGH THE UPPER INTERMOUNTAIN WEST/NORTHERN ROCKIES...THESE DIFFERENCES SEEM TO BE WELL WITHIN THE ENSEMBLE SPREAD. THE 12Z GFS AND 00Z ECMWF/UKMET APPEAR TO REMAIN CLOSE TO THE CENTER OF THE MODEL SPREAD THROUGHOUT THE PERIOD SO WILL FAVOR A BLEND AMONG THESE MODELS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... RUBIN-OSTER