MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 258 AM EDT THU MAY 15 2014 VALID MAY 15/0000 UTC THRU MAY 18/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ============================================== 00Z MODEL EVALUATION AND PREFERENCES ============================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ============================================== ...SYSTEM MOVING THROUGH THE EAST... PREFERENCE: BLEND OF 00Z GFS/ECMWF CONFIDENCE: AVERAGE THE 00Z ECMWF AND UKMET TRENDED SLIGHTLY QUICKER TO OPEN THE MID LEVEL CIRCULATION AND ADVANCE THE TROUGH AXIS TOWARD NEW ENGLAND. OF THESE TWO...THE UKMET IS THE FASTER MODEL...ALTHOUGH ITS SURFACE SOLUTION IS VERY SIMILAR TO THE ECMWF. THE GFS REMAINED SLOWER AND FORECASTS LESS EROSION OF LOWER HEIGHTS OVER THE MIDWEST ON SATURDAY...WHEREAS THE ECMWF/UKMET BRING MORE WARM ADVECTION AND MID LEVEL RIDGING INTO THAT REGION. THESE DIFFERENCES OWE PARTLY TO THE GFS WRAPPING A DEEPER SHORTWAVE AROUND THE BASE OF THE TROUGH AND PARTLY TO THE ECMWF MORE AGGRESSIVELY PHASING SHORTWAVES OVER THE GREAT LAKES AND SOUTHERN CANADA. WITH NO SOLUTION PROVING IDEAL...WE RECOMMEND BLENDING THE GFS/ECMWF TO SMOOTH THEIR SHORTWAVE DIFFERENCES. THE NAM APPEARED VERY USABLE THROUGH DAY 2. IT IS LEFT OFF OUR PREFERENCE BECAUSE ITS HANDLING OF OTHER SYSTEMS ON DAY 3 BEGINS TO SWAY THE HEIGHT STRUCTURE OVER THE EASTERN U.S. THE NAM ALSO DISPLAYS ITS TYPICAL BIAS OF BEING COOLER IN THE MID LEVELS COMPARED TO THE GLOBAL MODEL CONSENSUS. ...WAVE IN NORTHWEST FLOW REACHING THE SOUTHERN PLAINS LATE FRIDAY... PREFERENCE: BLEND OF 00Z OPERATIONAL MODELS...EXCLUDING THE NAM CONFIDENCE: AVERAGE THIS WAVE CARRIES A SMALL SCALE BUT WELL DEFINED PRECIPITATION EVENT WITH IT INTO THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY...WHILE ALSO PRODUCING A FRONTAL SURGE THROUGH OK/TX/ERN NM. ALTHOUGH ALL MODELS ARE SIMILAR AT THE SURFACE THROUGH SATURDAY MORNING...THE 00Z NAM WAS NOT PREFERRED FOR ITS HANDLING OF THE UPPER PATTERN. THE NAM APPEARED FAST WITH THE WAVE IN QUESTION HERE...WHILE THE CANADIAN HAD IMPROVED SINCE THE 12Z RUN. ...DEEP TROUGH APPROACHING THE PACIFIC NORTHWEST... PREFERENCE: BLEND OF 00Z ECMWF/UKMET/CANADIAN CONFIDENCE: AVERAGE THE NAM WAS A FAST OUTLIER AS EARLY AS 48 HOURS INTO THE FORECAST. OTHERWISE THERE WAS DECENT AGREEMENT AMONG THE GLOBAL MODELS ON THE LARGE SCALE...BUT THE 00Z GFS DOES BECOME FLAT WITHIN THE BASE OF THE TROUGH ON THE WEST COAST ON DAY 3. THE GFS WAS ALSO FAST WITH DOWNSTREAM RIDGING OVER THE DAKOTAS...AND WENT THROUGH SOME MARKED RUN TO RUN CHANGES BETWEEN THE 14/12Z AND 15/00Z CYCLES. ALTHOUGH THE GFS MAY STILL BE USEFUL HERE...WE HAVE GREATER CONFIDENCE IN THE DETAILS OF THE ECMWF/UKMET/CANADIAN. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BURKE