MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1127 AM EST SAT FEB 08 2014 VALID FEB 08/1200 UTC THRU FEB 12/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION WITH PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. SYSTEM APPROACHING WESTERN US/CANADIAN BORDER TUESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: CANADIAN/GFS COMPROMISE CONFIDENCE: BELOW AVERAGE A SYSTEM WITH SOME AMPLITUDE IS ATTEMPTING TO MOVE THROUGH QUICK FLOW OVER THE TOP OF BROAD SOUTHERN STREAM RIDGING OFFSHORE THE WEST COAST. THE SWIFT SYSTEM MOVEMENT LEADS TO CONFIDENCE NO BETTER THAN AVERAGE TO START WITH. WITH ABOVE AVERAGE DETERMINISTIC AND GEFS/ECMWF ENSEMBLE MEAN SPREAD HERE, CONFIDENCE FALLS TO BELOW AVERAGE. THE GUIDANCE WHICH SPLITS THE DIFFERENCE IN THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS ARE THE 00Z CANADIAN/12Z GFS RUNS. A COMPROMISE OF THEIR SOLUTIONS IS PREFERRED WITH BELOW AVERAGE CONFIDENCE. INTERMEDIATE SHORTWAVE MOVING THROUGH OH VLY TUESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: UKMET/CANADIAN COMPROMISE CONFIDENCE: ABOVE AVERAGE THE 00Z UKMET/00Z CANADIAN SOLUTIONS ARE QUICKER/WEAKER WITH THIS SYSTEM THAN THE OTHER GUIDANCE. IN THE SPACE BETWEEN A PIECE OF THE POLAR VORTEX UP IN NUNAVUT, ANOTHER TROUGH PROGRESSING THROUGH ATLANTIC CANADA, AND A SHORTWAVE DIGGING INTO TEXAS, THIS SYSTEM SHOULD HAVE MINIMAL AMPLITUDE AND BE QUICK-MOVING, EMBEDDED WITHIN QUASI-ZONAL FLOW. THE 12Z GFS/12Z NAM MAKE THE CLASSIC MISTAKE -- SEEN OCCASIONALLY IN ALL THE MODEL GUIDANCE FROM TIME TO TIME -- OF AMPLIFYING THIS INTERMEDIATE STREAM SHORTWAVE DESPITE NO RIDGING UPSTREAM AND ONLY MINIMAL NORTHERN STREAM RIDGING TO ITS NORTH ACROSS SOUTHWEST QUEBEC. THE NAM ALSO HAS A BIAS OF BECOMING TOO STRONG WITH SYSTEMS MOVING THROUGH THE WESTERLIES. USING THE SYNOPTIC PATTERN AS THE PRIMARY GUIDE, PREFER A UKMET/CANADIAN COMPROMISE SOLUTION HERE WITH ABOVE AVERAGE CONFIDENCE. SHORTWAVE DIGGING INTO TEXAS LATE TUESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: CANADIAN/UKMET/ECMWF COMPROMISE CONFIDENCE: AVERAGE A BUILDING, BROAD RIDGE OFFSHORE THE WEST COAST IS EXPECTED TO SHARPEN A SOUTHERN STREAM TROUGH DOWNSTREAM ACROSS TX TUESDAY. THE 12Z GFS IS WEAKER THAN ITS 06Z GEFS MEAN HERE, IMPLYING THAT ITS SOLUTION IS TOO WEAK. THE 12Z NAM/12Z GFS LEAVE LESS DISTANCE BETWEEN THIS SYSTEM AND A FAIRLY WEAK INTERMEDIATE STREAM SHORTWAVE MOVING THROUGH THE OHIO VALLEY, WHICH APPEARS TO LEAD TO A WEAKER TX SHORTWAVE. SYSTEM MOVING THROUGH THE OH VLY/NORTHEAST SUN & MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-GFS COMPROMISE CONFIDENCE: ABOVE AVERAGE THE 12Z GFS IS THE STRONGEST PIECE OF GUIDANCE AT THE SURFACE AND ALOFT WITH THIS SYSTEM. AS IT IS MOVING UNDER THE BASE OF A CLOSED CYCLONE CENTERED IN QUEBEC/LABRADOR, THE SYSTEM IS MORE LIKELY TO BE BROAD/SHEARED OUT THAN AMPLIFIED, WHICH ARGUES AGAINST THE STRONGER 12Z GFS/06Z GEFS MEAN/09Z SREF MEAN SOLUTIONS. EVEN THE NAM, WHICH CAN DISPLAY A STRONG BIAS WITH SYSTEMS IN THE WESTERLIES, SHOWS A WEAKER OVERALL SOLUTION WITH THIS SYSTEM. GFS TRENDS SINCE ITS 06Z RUN ALSO ARGUE FOR A WEAKER SOLUTION. WITH THE ABOVE IN MIND, PREFER A DETERMINISTIC BLEND OF THE NON-GFS GUIDANCE WITH ABOVE AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... ROTH