MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1215 PM EDT SUN APR 20 2014 VALID APR 20/1200 UTC THRU APR 24/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z GFS/NAM EVALUATION WITH PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. PAIR OF CYCLONES APPROACHING THE PAC NW TUE & WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GFS/NAM/ECMWF COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE IS IN EXCELLENT AGREEMENT WITH THE TUESDAY SYSTEM. FOR LATE WEDNESDAY, THE 00Z UKMET OUTRACES THE REMAINDER OF THE DETERMINISTIC GUIDANCE, LYING ON THE NORTHEAST FRINGE OF THE 00Z GLOBAL ENSEMBLE SPREAD -- ITS USUAL BIAS. A COMPROMISE OF THE 12Z GFS/12Z NAM/00Z ECMWF KEEPS THE SYSTEM WITHIN THE BEST 00Z GLOBAL ENSEMBLE CLUSTERING, SO PREFER THIS COMPROMISE WITH ABOVE AVERAGE CONFIDENCE. DEEP UPPER TROUGH MOVING THROUGH THE WEST TUE/WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM COMPROMISE CONFIDENCE: ABOVE AVERAGE THE 12Z NAM IS MORE NORTHEASTERLY WITH THE MAIN CYCLONE/MAIN 500 HPA SHORTWAVE NEAR THE WESTERN US/CANADIAN BORDER THAN THE OTHER DETERMINISTIC GUIDANCE -- ITS SOLUTION IS ON THE NORTHEAST FRINGE OF THE 00Z GLOBAL ENSEMBLE GUIDANCE. WITH NORTHERN STREAM RIDGING STEADFAST ACROSS NORTHERN ALBERTA, BELIEVE THE CONSENSUS SHOWING A MORE EASTERLY TRACK IS CORRECT HERE. THE PREFERENCE IS FOR A NON-NAM COMPROMISE WITH ABOVE AVERAGE CONFIDENCE CONSIDERING THE SYNOPTIC PATTERN IN WHICH THE SYSTEM IS EMBEDDED. SYSTEM MOVING ACROSS THE GREAT LAKES/NEW ENGLAND TUE & WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: ECMWF/GFS/NAM COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 00Z UKMET/CANADIAN ARE STRONGER ALOFT WITH THIS SYSTEM, WHICH ALLOWS THEM TO MAINTAIN A CYCLONE WITH A MORE NORTHWEST TRACK ACROSS SOUTHEAST ONTARIO/QUEBEC THAN SEEN ON THE OTHER DETERMINISTIC GUIDANCE. THE 00Z GLOBAL ENSEMBLE GUIDANCE HAS TRENDED SLIGHTLY AWAY FROM THIS SOLUTION SINCE ITS 19/00Z RUN, WITH ABOUT 1/4 OF THE MEMBERS FAVORING AN IDEA TOWARDS THE UKMET/CANADIAN SOLUTIONS. BOTH PIECES OF GUIDANCE CAN BE TOO STRONG ALOFT. THE PREFERENCE IS FOR A COMPROMISE OF THE 00Z ECMWF/12Z GFS/12Z NAM SOLUTIONS WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE CONSIDERING TRENDS SEEN IN THE GLOBAL ENSEMBLE GUIDANCE. DEEP UPPER TROUGH DEPARTING THE SOUTHEAST TODAY WEAK MID-LEVEL SHORTWAVE PASSING JUST NORTH OF MAINE ON MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: HIGH THE MODELS SHOW EXCELLENT AGREEMENT. A GENERAL MODEL COMPROMISE IS PREFERRED TO IRON OUT ANY SMALLER SCALE DETAIL DIFFERENCES WITH HIGH CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... ROTH