MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 214 PM EST THU FEB 27 2014 VALID FEB 27/1200 UTC THRU MAR 03/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ============================================== 12Z MODEL EVALUATION AND PREFERENCES ============================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ============================================== ...STRONG SYSTEM IN THE SOUTHWEST FRI/SAT LATER REACHING THE PLAINS... PREFERENCE: BLEND OF 12Z GFS/ECMWF/CANADIAN CONFIDENCE: AVERAGE THERE ARE FEW DIFFERENCES THROUGH DAY 2...ALTHOUGH BY 02/00Z THE ECMWF BEGINS TO SHOW QUICKER SPEED AND LESSER AMPLITUDE...WHILE THE GFS MAINTAINS A SMALL CLOSED 500 MB CENTER AT THE BASE OF THE TROUGH ALONG THE SOUTHERN CALIFORNIA COAST. NEAR AND BENEATH THIS COLD CORE LOW THE GFS PRECIPITATION OUTPUT DIFFERS FROM THE OTHER MODELS ON DAY 2...WITH MUCH OF IT FALLING NEAR THE COAST RATHER THAN IN THE MOUNTAINOUS TERRAIN. WITH STEEPENING LAPSE RATES THE PRECIPITATION REGIME MAY EXPERIENCE SOME WEAK CONVECTIVE ENHANCEMENT...BUT THERE APPEARS TO BE CONTINUED MOIST ONSHORE FLOW...ESPECIALLY ABOVE 850 MB...AND ANY CONVECTIVE CELLS WOULD ALSO MOVE INLAND. SO THE DISCUSSION AMONG THE WPC DESKS HAS BEEN TO WEIGHT WPC DAY 2 PRECIPITATION FORECASTS MORE TOWARD THE NON-GFS CONSENSUS. PLEASE SEE THE QPFPFD AND QPFHSD FOR DETAILS. THIS SYSTEM OPENS UP FURTHER ON DAY 3 AS IT APPROACHES THE PLAINS AND BEGINS TO INTERACT WITH A LOW LEVEL WAVE FORMING ALONG AN ARCTIC FRONTAL ZONE. AGREEMENT IS FAIR AT THE SURFACE...BUT TIMING DIFFERENCE ALOFT BECOME MORE EXAGGERATED. ON THE 00Z CYCLE THE ECMWF AND ECMWF ENSEMBLE MEAN SPED UP FROM THE 03/00Z POSITION THEY HAD BEEN FORECASTING FOR SEVERAL RUNS. THE 12Z ECMWF TRENDED SLIGHTLY SLOWER AND HAS SUPPORT FROM THE CANADIAN. THE NAM REPRESENTS THE SLOW SIDE OF THE SPREAD... AND THE GFS/GEFS ARE IN THE MIDDLE. TAKING A CONSENSUS APPROACH WE PREFER THE GFS/GEFS...BUT THE 12Z ECMWF AND CANADIAN ARE CLOSE ENOUGH TO BE BLENDED TOGETHER WITH THE GFS TO FORM A BROAD CONSENSUS. ...SHORTWAVE SWINGING THROUGH THE GREAT LAKES/NORTHERN NEW ENGLAND THIS WEEKEND... ...ARCTIC FRONT DIPPING INTO THE PLAINS/MIDWEST... PREFERENCE: BLEND OF 12Z GFS/ECMWF/CANADIAN CONFIDENCE: AVERAGE ASIDE FROM THE SLOW UKMET...THE MODELS ARE SIMILAR IN MOVING LOW PRESSURE THROUGH SOUTHEAST CANADA. GREATER UNCERTAINTY EXISTS AS TO THE SOUTHWARD PUSH OF THE ATTENDANT COLD FRONT INTO VIRGINIA. THE BOUNDARY WILL SLOW DOWN BENEATH A STRENGTHENING CONFLUENT FLOW...WEST-SOUTHWESTERLY...ALOFT. THE 12Z ECMWF TRENDED SLIGHTLY FARTHER SOUTH. THE GFS IS STILL AT THE SOUTHERN EDGE OF THE SPREAD. THE NAM IS NOT QUITE AS AGGRESSIVE AS THE ENSEMBLE MEANS...ESPECIALLY JUDGING BY THE COLD AIR AT 850 MB. AVERAGING THE SOLUTIONS FROM THE SURFACE TO ALOFT...A BLEND OF THE 12Z GFS/ECMWF/CANADIAN APPEARS TO REPRESENT CONSENSUS EQUALLY AS WELL AS A BLEND OF THE 12Z GEFS MEAN WITH 00Z ECMWF ENSEMBLE MEAN. ...UPPER LOW CLOSING OFF OVER SOUTHWEST CANADA... PREFERENCE: BLEND OF 12Z NAM/ECMWF/CANADIAN CONFIDENCE: AVERAGE THE NAM/ECMWF/CANADIAN DO THE BEST JOB OF CLOSING OFF THIS FEATURE ON DAY 2 AND MIGRATING IT WESTWARD. THE GFS TRENDED IN THE RIGHT DIRECTION BUT WAS STILL SLOW TO PRODUCE HEIGHT FALLS BACK TOWARD WASHINGTON AND BRITISH COLUMBIA. ON THE OTHER HAND...THE ECMWF MAY BE OVERDONE WITH A PACIFIC SHORTWAVE THAT PHASES WITH THIS SYSTEM ON DAY 3...AFFECTING WASHINGTON/OREGON. GIVEN THAT THE ECMWF HANDLING OF THIS DAY 3 SHORTWAVE IS LESS THAN IDEAL...WE RECOMMEND BLENDING IT TOWARD THE NAM/CANADIAN. ...SHORTWAVE AT THE FOUR CORNERS THIS EVENING AND CRUISING EAST... PREFERENCE: BLEND OF THE OPERATIONAL MODELS CONFIDENCE: AVERAGE LOOKING BACK OVER SEVERAL RUNS THE ECMWF HAS BEST HANDLED THE LIKELY DEPTH THIS WAVE WILL ACHIEVE AS IT MOVES OFF THE SOUTHERN ATLANTIC COAST ON DAY 2. THE OTHER MODELS HAVE TRENDED ENOUGH TOWARD THAT DEPTH...THAT ANY ONE OF THEM HAS A REASONABLE DEPICTION OF THIS SYSTEM...PARTICULARLY WHILE IT IS TRAVERSING THE SOUTHERN U.S. ON DAYS 1 AND 2. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE