MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 243 PM EDT MON APR 21 2014 VALID APR 21/1200 UTC THRU APR 25/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ============================================== 12Z NAM/GFS EVALUATION AND PREFERENCES ============================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ============================================== ...FRONT SWEEPING THE EAST AND CLOSED LOW FORMING NEAR NEW ENGLAND... PREFERENCE: NON-NAM CONSENSUS CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS HAVE MOVED TOWARD BETTER AGREEMENT...WITH THE ECMWF AND CANADIAN SLOWING DOWN SLIGHTLY TOWARD THE GFS/UKMET. THE ECMWF IS QUITE A BIT DEEPER WITH A SHORTWAVE ROUNDING THE BASE OF THE TROUGH EARLY WEDNESDAY...BUT ITS SOLUTION MOVES BACK TOWARD CONSENSUS SHORTLY THEREAFTER. THERE ARE NO STRONG OUTLIERS...BUT THE 12Z NAM PRODUCED A DEEPER/SLOWER SOLUTION BEGINNING AROUND THE END OF DAY 2...24/00Z. THEREFORE...THE GLOBAL MODEL CONSENSUS IS PREFERRED OVERALL...BUT THE NAM MAY STILL BE USEFUL THROUGH DAY 2. ...LARGE TROUGH AFFECTING THE WEST AND THEN THE PLAINS... PREFERENCE: BLEND OF 12Z GFS/ECMWF CONFIDENCE: AVERAGE THERE ARE FEW LARGE SCALE DIFFERENCES FOR THIS SYSTEM EARLY IN THE PERIOD WHEN IT IS OVER THE WEST. A SEASONABLY VIGOROUS CLOSED LOW SHOULD FORM NEAR THE INTERNATIONAL BORDER WHEN THE TROUGH SWINGS INTO A NEUTRAL OR SLIGHT NEGATIVE TILT UPON EXITING THE INTERMOUNTAIN WEST. MODELS ARE ALL SIMILAR IN TIMING THE ATTENDANT COLD FRONT THROUGH THE SOUTHERN PLAINS AND LOWER MISSOURI VALLEY ON DAY 3. DIFFERENCES ARE MORE MARKED AND SOLUTIONS ARE MORE VARIABLE FROM RUN TO RUN UP NORTH. AT THE SURFACE AN OCCLUDING LOW SHOULD REMAIN ANCHORED BENEATH THE UPPER CIRCULATION ON THE INTERNATIONAL BORDER...WHILE A SECOND LOW FORMS ON THE TRAILING COLD FRONT IN THE MIDWEST OWING TO A SHARP SHORTWAVE. THE UKMET PHASES THE TWO SURFACE LOWS IN A FASHION THAT LOOKS UNREALISTIC. THERE IS BETTER AGREEMENT NOW AMONG THE GFS/ECMWF/CANADIAN/NAM. THE CANADIAN IS ON THE SLOW SIDE...ESPECIALLY ALOFT. THE NAM IS ON THE FAST SIDE AND IS SOMEWHAT WEAKER OVERALL. THIS LEADS US TO RECOMMEND A GFS/ECMWF BLEND TO REPRESENT CONSENSUS. ...BROAD TROUGH REACHING THE PACIFIC NORTHWEST THURSDAY... PREFERENCE: BLEND OF 12Z GFS/ECMWF/UKMET/CANADIAN CONFIDENCE: SLIGHTLY ABOVE AVERAGE MODELS CONTINUE IN GOOD AGREEMENT ON THE LARGE SCALE. THE NAM IS ONE OF THE FLATTER SOLUTIONS WHEN VIEWED AT 500 MB...AND IT PUSHES THE DOWNSTREAM SHORTWAVE RIDGE FARTHER INLAND ON DAY 3. ON THE OTHER HAND THE NAM TIMES THE MOVEMENT OF THE TROUGH SIMILARLY TO THE THE GLOBAL MODELS...AND ITS SOLUTION FROM THE SURFACE TO 700 MB ALSO FITS WITH CONSENSUS SUCH THAT THE NAM COULD BE USED HERE. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE