MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1149 PM EST THU JAN 30 2014 VALID JAN 31/0000 UTC THRU FEB 03/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... ================================================== 00Z NAM/GFS EVALUATION AND PRELIMINARY PREFERENCES ================================================== NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO SIGNIFICANTLY AFFECT THEIR LARGE SCALE OUTPUT. ================================================== ...SYSTEM TRAVERSING THE NATION AND LEAVING A BROAD SWATH OF RAIN/ICE/SNOW... PREFERENCE: BLEND OF 00Z GFS/12Z GFS THIS SYSTEM IS MARKED BY PHASING OF SOUTHERN AND NORTHERN STREAM SHORTWAVES WHICH ENTER THE CENTRAL U.S. AND THEN PUSH A SURFACE LOW QUICKLY UP THE OHIO VALLEY TOWARD NEW ENGLAND. MODELS ARE FAIRLY SIMILAR WITH RESPECT TO SYSTEM STRENGTH AND THERMAL FIELDS...BUT THEY DISPLAY SUBTLE TIMING DIFFERENCES. THE GFS AND ECMWF HAVE BEEN RELATIVELY CONSISTENT...AND THE ENSEMBLES SUPPORT THEM. ENSEMBLE LOW PLOTS CLUSTER NICELY AROUND THE GFS/ECMWF SOLUTIONS...AND INDICATE LOW PRESSURE NEAR MONTREAL CANADA AT 02/12Z. THE 00Z NAM AND 12Z CANADIAN BECOME FASTER THAN THE ENSEMBLE CONSENSUS AFTER 01/12Z. THIS IS PARTICULARLY NOTICEABLE IN THE LOW LEVEL FIELDS WHEREAS THE MID LEVEL DIFFERENCES REMAIN MINIMAL. THE 12Z UKMET WAS SLOWER THAN CONSENSUS AND WAS ALSO SEVERAL MILLIBARS WEAKER AT THE CENTER OF THE SURFACE LOW. ...STRONG TROUGH REACHING SOUTHERN CALIFORNIA BY MONDAY MORNING... PREFERENCE: BLEND OF 00Z GFS WITH 12Z ECMWF/UKMET COMPARING SPAGHETTI PLOTS OVER THREE MODEL CYCLES ENDING WITH THE 30/12Z CYCLE...THE OPERATIONAL MODELS AND ENSEMBLES ARE TIGHTLY CLUSTERED AND CONSISTENT FROM RUN TO RUN. THE MEANS BEST SUPPORT THE GFS/ECMWF/UKMET. THE 12Z CANADIAN WAS SLIGHTLY FASTER AND LESS AMPLIFIED THAN THIS CLUSTER. THE 18Z NAM HAD BEEN A VERY SLOW OUTLIER...AND ALTHOUGH THE 00Z RUN IS FASTER...IT DOES NOT QUITE CATCH UP TO THE PREFERRED SOLUTION. WE WILL CONTINUE TO RECOMMEND THE GFS/ECMWF AND ADD THE 12Z UKMET. ...BROAD TROUGHING STRETCHING FROM THE PACIFIC NORTHWEST TO UPPER MIDWEST BY MONDAY... REFERENCE: BLEND OF 00Z NAM WITH 12Z ECMWF DEEP NORTHERLY FLOW IN BETWEEN THE PACIFIC/ALASKAN RIDGE AND HUDSON BAY LOW WILL FAVOR A CONTINUED FEED OF ARCTIC AIR REACHING U.S. GIVEN RECENT RETROGRESSION OF THE RIDGE...THE ARCTIC AIR WILL PENETRATE FARTHER WEST INTO WASHINGTON AND IDAHO...AND WILL REMAIN ENTRENCHED FARTHER EAST. ON DAY 3 THE COLD AIR WILL UNDERGO GRADUAL DEEPENING AS MID LEVEL SHORTWAVES SWING INTO THE NORTHERN U.S. THE MODELS SHOW GOOD AGREEMENT NEAR THE CORE OF THE COLD AIR FROM CENTRAL CANADA TO NORTH DAKOTA/MINNESOTA. OUT WEST THERE ARE SOME DIFFERENCES WITH A SHORTWAVE THAT ORIGINATES OVER YUKON PROVINCE. JUDGING BY THE ENSEMBLES...THE SLOWER 12Z UKMET AND CANADIAN RUNS WERE OUTLIERS. AGREEMENT AMONG THE 00Z NAM/GFS...WITH SUPPORT OF THE 12Z ECMWF...ALSO GIVES US SOME CONFIDENCE IN RECOMMENDING THE FASTER SOLUTIONS. THE GFS...HOWEVER...MAY BE SLIGHTLY TOO FAST...AND APPEARS GENERALLY LESS WELL DEFINED WITH SOME OF THE SHORTWAVES IN THIS NORTHERN STREAM FLOW. ...SHORTWAVE CROSSING FLORIDA TODAY THROUGH SATURDAY... PREFERENCE: ANY OF 00Z GFS OR 12Z ECMWF/UKMET THIS MID LEVEL WAVE WILL SUPPORT CONTINUED RAIN AS IT SLIDES ALONG AND NORTH OF A STALLED FRONTAL BOUNDARY. THERE ARE SOME MINOR TIMING DIFFERENCES IN THE MODELS. THE GFS/ECMWF/UKMET CLUSTER WELL...AND HAVE SUPPORT FROM THE ENSEMBLE MEANS. THE 00Z NAM IS VERY CLOSE TO THIS CONSENSUS...BUT DOES START TO LAG BEHIND BY DAY 2. THE CANADIAN HAS CONSISTENTLY BEEN ONE OF THE SLOWEST SOLUTIONS. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE