MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 159 PM EST THU FEB 20 2014 VALID FEB 20/1200 UTC THRU FEB 24/0000 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. ============================================== ...GREAT LAKES CYCLONE AND COLD FRONT SWEEPING TO THE EAST COAST... PREFERENCE: NONE CONFIDENCE: ABOVE AVERAGE THE MODELS ARE NOW VERY NICELY CLUSTERED WITH THE TRACK AND INTENSITY OF THE SURFACE CYCLONE THROUGHOUT ITS LIFE CYCLE. THE 850 MB HEIGHT ANOMALIES IN THE GFS/GEFS ARE 4.5 STANDARD DEVIATIONS FROM CLIMATOLOGY FOR THE MATURING SYSTEM AS IT PASSES THROUGH WISCONSIN AND THE U.P. OF MICHIGAN. THE ECMWF AND CANADIAN TRENDED TOWARD AGREEMENT WITH THE NAM/GFS/UKMET ON DAY 3 IN NUDGING THE MATURE CYCLONE EASTWARD ACROSS CANADA. THIS OCCURS IN RESPONSE TO A SUBTLE KICKER DIVING THROUGH WESTERN CANADA. THE MODEL SPREAD HAS ALSO DIMINISHED WITH RESPECT TO THE FORWARD SPEED OF THE ATTENDANT COLD FRONT. ...ARCTIC FRONT PUSHING TOWARD THE SOUTHERN STATES THIS WEEKEND... ...RAIN BREAKING OUT NEAR THE GULF COAST SUNDAY... PREFERENCE: BLEND OF 12Z NAM/GFS/ECMWF CONFIDENCE: AVERAGE WITH BROAD TROUGHING ESTABLISHED OVER CENTRAL NORTH AMERICA...AND ANOTHER ANOMALOUS RIDGE BUILDING OVER ALASKA...ARCTIC AIR WILL BUILD SOUTHWARD. THE LEADING EDGE OF COLD AIR IS PREDICTED INTO THE SOUTHERN STATES BY SUNDAY...WITH AN ASSOCIATED TIGHTENING OF A MID LEVEL CONFLUENCE ZONE AND INCREASE OF PRECIPITATION ALONG THE GULF COAST. THE MODELS HAVE SHOWN REASONABLE AGREEMENT AT THE SURFACE. THE GFS INDICATES A SLIGHTLY MORE AMPLIFIED SURFACE PATTERN...WITH LOW PRESSURE POTENTIALL FORMING IN THE MID ATLANTIC SUNDAY AND HOLDING UP THE FRONTAL PROGRESSION THERE. ALTHOUGH THIS DOES NOT YET HAVE MUCH SUPPORT...IT IS POSSIBLE...ESPECIALLY CONSIDERING THAT THE ECMWF HAS TENDED TO BE VERY FLAT AND ILL DEFINED WITH SHORTWAVES IN THE WAKE OF THE MIDWESTERN CYCLONE. ASIDE FROM THIS DIFFERENCE...THE NAM/GFS/ECMWF SOLUTIONS ARE VERY SIMILAR...AND DIFFERENCES ALOFT ARE FAIRLY MINOR. THE CANADIAN DOES APPEAR MORE FLAT AND PROGRESSIVE. THE UKMET IS SHARPER AND DEEPER WITH A SHORTWAVE ARRIVING IN THE PLAINS SUNDAY. AVERAGING THE MODEL SOLUTIONS FROM THE SURFACE TO 500 MB THE BEST CLUSTER APPEARS TO BE THE NAM/GFS/ECMWF...ALTHOUGH THE QPF IN THE NAM IS ON THE LIGHT SIDE. SEE THE QPFPFD FOR PRECIPITATION PREFERENCES. ...SHORTWAVE DIPPING TOWARD THE NORTHWEST U.S. SUNDAY... PREFERENCE: BLEND OF 12Z GFS/ECMWF/UKMET CONFIDENCE: AVERAGE THIS FEATURE HAS BEEN STABLE FROM RUN TO RUN IN THE GFS/ECMWF/UKMET AND GFS/ECMWF ENSEMBLES. THE NAM IS SIMILAR BUT INDICATES A MORE NARROW AND ELONGATED TROUGH. GIVEN THAT ITS TIMING AND PLACEMENT MEETS CONSENSUS...THE NAM MAY STILL BE USED HERE...BUT FOR THE LARGE SCALE PATTERN THE NAM IS LEFT OUT OF OUR PREFERENCE. THE CANADIAN IS MORE AGGRESSIVE WITH PACIFIC ENERGY BREAKING DOWN SHORTWAVE RIDGING NEAR COASTAL WASHINGTON...BUT IT IS NOT FAR FROM CONSENSUS WITH THE WAVE DROPPING OUT OF CANADA. ...SHORTWAVE MOVING INTO CALIFORNIA SATURDAY... PREFERENCE: 12Z GFS CONFIDENCE: AVERAGE THIS WEAK FEATURE APPEARS TO CARRY LITTLE MOISTURE OR LIFT WITH IT...AND THE MODEL SOLUTIONS ARE DRY...SUGGESTING LITTLE IMPACT. THE NAM AND GFS ARE DOING A BETTER JOB OF AT LEAST INDICATING SOME BUMP TO THE HEIGHT FIELD. OTHER GLOBAL MODELS AT LEAST SHOW SOME INDICATION OF THIS SYSTEM IN THE VORTICITY FIELD...AND THEIR PROGRESSION OF THE FEATURE FAVORS THE GFS RATHER THAN THE SLOWER NAM. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE