MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 250 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 MODEL EVALUATION...INCLUDING FINAL 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 GUIDANCE 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: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE SURFACE LOW ADJUSTMENTS BY THE 12Z CMC COMPARED TO ITS PREVIOUS CYCLE ARE IN THE DIRECTION OF THE REMAINING MODELS...THROUGH 00Z INTO THE KS/MO BORDER TONIGHT. THIS FEATURE BECOMES INDISTINGUISHABLE BEYOND ABOUT 06Z TONIGHT AND THE LATEST DETERMINISTIC/ENSEMBLE GUIDANCE NOW 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: BLEND OF THE 12Z ECMWF/00Z ECMWF MEAN CONFIDENCE: AVERAGE THE ECMWF/CMC HAVE GENERALLY 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 12Z ECMWF/CMC ADJUSTED NORTH SLIGHTLY WITH THE MID-LEVEL LOW AND SURFACE LOW TRACKS BUT NOT TO THE EXTENT OF THE 12Z GFS. THE GFS HAS BEEN SOMEWHAT INCONSISTENT FROM RUN TO RUN AND THE 12Z GFS HAS ADJUSTED NORTH FROM PREVIOUS CYCLES...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 AND THE 00Z ECMWF APPEARS TO BE ON THE SRN EDGE OF THE LATEST ENSEMBLE GUIDANCE. THE 12Z ECMWF MAY BE A HAIR TOO FAR NORTH GIVEN THE LATEST ENSEMBLE DISTRIBUTION BUT WHEN BLENDED WITH THE SLOWER/MORE-SOUTH 00Z ECMWF MEAN...A PREFERRED COMPROMISE IS REACHED. 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 SLIGHTLY SOUTH/SLOWER COMPARED TO THE SLIGHTLY MORE NORTHERN 12Z ECMWF AND THE SIGNIFICANTLY FARTHER NORTH 12Z GFS POSITION ON SUN. FOR MON...THE 12Z ECMWF/00Z ECMWF ARE RATHER SIMILAR TO ONE ANOTHER. ...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC NORTHWEST SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE 12Z UKMET ADJUSTED SLIGHTLY FASTER TOWARD THE REMAINING MODEL CONSENSUS...INCREASING CONFIDENCE IN THE LATEST WELL CLUSTERED MODEL CONSENSUS.REGARDING THE PROGRESSION OF THE UPPER TROUGH AND SURFACE LOW THROUGH 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