MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1258 PM EDT FRI APR 28 2017 VALID APR 28/1200 UTC THRU MAY 02/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...COLD FRONT CLEARING THE NORTHEAST EARLY FRI... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE ONLY VERY MODEST MASS FIELD SPREAD IS NOTED WITH THIS SYSTEM. A GENERAL MODEL BLEND SHOULD SUFFICE. ...UPPER LOW OVER SOUTHERN ALBERTA MOVING SLOWLY EAST ACROSS SASKATCHEWAN BY SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE ONLY MINOR TIMING/DEPTH DIFFERENCES WITHIN THE MODELS WERE NOTED WITH THIS SYSTEM AS IT SLOWLY MOVES EAST INTO SASKATCHEWAN BY SAT...BUT THE MODELS AGREE IN DAMPENING THE ENERGY OUT BY SUN. NO SIGNIFICANT TRENDS WERE NOTED IN THE 12Z NAM/GFS COMPARED TO PREVIOUS RUNS...UNTIL PERHAPS MUCH LATER IN THE FORECAST PERIOD AS THE ENERGY IS SHEARING EAST ACROSS NRN ONTARIO. A GENERAL MODEL BLEND IS PREFERRED. ...INITIAL TROUGH/HEIGHT FALLS OVER THE HIGH PLAINS TODAY WITH WEAKENING SURFACE LOW TRACKING EAST FROM KANSAS THIS MORNING... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 00Z CMC BLEND CONFIDENCE: ABOVE AVERAGE THE 00Z CMC STANDS OUT WITH A MUCH STRONGER SURFACE LOW...RELATIVE TO THE OTHER MODELS...THROUGH 00Z INTO THE KS/MO BORDER TONIGHT. THE 00Z CMC IS ALREADY 3-4 MB STRONGER WITH THE SURFACE LOW COMPARED TO 15Z OBSERVATIONS AND IS LIKELY OVER DEVELOPED WITH THIS FEATURE GIVEN ITS STRONGER MID-LEVEL REFLECTION. THIS FEATURE BECOMES INDISTINGUISHABLE BEYOND ABOUT 06Z TONIGHT. THE REMAINING DETERMINISTIC/ENSEMBLE GUIDANCE SHOWS SIMILARLY WITH THIS FEATURE. ...AMPLIFYING TROUGH OVER THE INTERMOUNTAIN WEST... ...CLOSED LOW DEVELOPMENT OVER THE FOUR CORNERS REGION FRI/SAT... ...SYSTEM EJECTING ACROSS THE PLAINS/MIDWEST THROUGH SUN/MON... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NEAR THE 00Z ECMWF BEAN CONFIDENCE: AVERAGE THE ECMWF/CMC HAVE BEEN MORE CONSISTENT WITH THE TIMING OF THE UPPER LOW AS IT REACHES THE PLAINS SUN MORNING BUT THE 00Z ECMWF/CMC ARE SOUTH OF THE REMAINING GUIDANCE. THE GFS HAS BEEN SOMEWHAT INCONSISTENT FROM RUN TO RUN AND THE 12Z GFS HAS ADJUSTED NORTH...AND LIES ON THE NRN EDGE OF THE LATEST ENSEMBLE SPREAD. TRENDS IN THE ENSEMBLES HAVE SHOWN A SLOWER SHIFT TOWARD THE SOUTH ON SUN ACROSS THE CNTRL PLAINS WITH THE 500 MB LOW BUT THE 00Z ECMWF APPEARS TO BE ON THE SRN EDGE OF THE LATEST ENSEMBLE GUIDANCE. THERE IS GROWING CONVERGENCE ON THE TIMING OF THE CLOSED LOW EJECTING OUT THROUGH THE PLAINS INTO THE UPPER MIDWEST WITH EACH ENSEMBLE CYCLE BUT THE ECMWF MEAN APPEARS TO BE THE MOST CONSISTENT AND REPRESENTS THE BEST CLUSTERING OF THE LATEST ECMWF/GEFS/CMC MEMBERS. THE 00Z ECMWF MEAN LIES BETWEEN THE SOMEWHAT SLOWER 00Z ECMWF AND THE FARTHER NORTH 12Z GFS POSITION. ...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC NORTHWEST SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE 00Z UKMET REMAINS SLIGHTLY SLOWER WITH THE PROGRESSION OF THE UPPER TROUGH AND SURFACE LOW TROUGH SWRN CANADA BUT DIFFERENCES ARE MINOR HERE AND ALMOST NON-EXISTENT ACROSS THE PACIFIC NORTHWEST. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ OTTO