MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 208 PM EST MON FEB 10 2014 VALID FEB 10/1200 UTC THRU FEB 14/0000 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. ============================================== ...EASTERN U.S. CYCLONE AND WINTER STORM... PREFERENCE: BLEND OF 12Z NAM/GFS/UKMET CONFIDENCE: AVERAGE ON THE LARGE SCALE A SIGNIFICANT WINTER STORM CERTAINLY APPEARS IN ALL OF THE OPERATIONAL MODELS. PRECIPITATION IS FOCUSED INITIALLY ALONG A MID LEVEL FRONTAL ZONE ORIENTED WEST TO EAST. LOW PRESSURE THEN DEVELOPS ALONG THE GULF COAST BY WEDNESDAY MORNING AND TRACKS TO JUST OFFSHORE OF THE MID ATLANTIC/DELMARVA TO NEW JERSEY BY THURSDAY AFTERNOON. ALL OF THE OPERATIONAL SOLUTIONS ARE PLAUSIBLE...BUT THERE ARE VERY MEANINGFUL STRENGTH/TRACK DIFFERENCES. OUR PREFERENCE IS BASED ON TRENDS IN SOME OF THE TIMING/STRENGTH/TRACK DETAILS. THE PAST TWO RUNS OF THE ECMWF HAVE BEEN ON THE WEST SIDE OF THE TRACK ENVELOPE WHILE ALSO BEING VERY STRONGLY DEVELOPED WITH THE SURFACE LOW. THE OPERATIONAL MODEL CONSENSUS IS TOWARD A LOW TRACK THAT IS MORE SUPPRESSED TO THE SOUTH ACROSS GEORGIA AND ADJACENT STATES ON DAY 2...AND THEN FARTHER EAST...SLIGHTLY OFFSHORE ON DAY 3. GIVEN THAT THE PARENT UPPER WAVE IS INITIALLY OF VERY LOW AMPLITUDE AND EMBEDDED IN FAST ZONAL FLOW...WE PREFER THE NON-ECMWF CONSENSUS. WE OMITTED THE CANADIAN FROM THIS CONSENSUS AS ITS SOLUTION IS SLIGHTLY FAST. THE NAM/GFS ARE LIKELY NOT PERFECT...BUT THEY HAVE TRENDED TOWARD THE ENSEMBLE MEANS...ESPECIALLY FOR TRACK AND TIMING. IT IS WORTH NOTING THAT THERE IS EVIDENCE FROM MULTIPLE RUNS OF THE ECMWF AND THE LATEST UKMET...AS WELL AS SEVERAL 12Z GEFS MEMBERS...THAT THE LOW LEVEL CYCLONE MAY DROP DEEPER THAN THE NAM/GFS SOLUTIONS BY 14/00Z. AN IMPORTANT NORTHERN STREAM SHORTWAVE HAD NOT YET COME ASHORE INTO BRITISH COLUMBIA THIS MORNING...SO SOME MARKED TRENDS MAY BE YET TO COME. THE 12Z NAM/GFS/UKMET...HOWEVER...ARE CONSISTENT WITH THE CURRENT TRENDS AND ENSEMBLE MEANS...WHICH GIVES US SOME CONFIDENCE IN RECOMMENDING THEM. ...SHORTWAVE INTO THE NORTHWEST LATE TUESDAY... ...SURFACE LOW FORMING IN EASTERN MONTANA LATE WEDNESDAY... PREFERENCE: BLEND OF 12Z ECMWF/UKMET/CANADIAN CONFIDENCE: AVERAGE THE MODELS SHOW GOOD AGREEMENT THROUGH DAY 2...00Z THURSDAY. ON DAY 3 DIFFERENCES ALOFT ARE FAIRLY MINOR...ALTHOUGH THE GFS/ECMWF ARE FLATTER AT 500 MB RELATIVE TO THE MORE AMPLIFIED NAM/UKMET/CANADIAN. WE BASED OUR PREFERENCES MORE ON THE SURFACE DIFFERENCES. THE NAM PUSHES THE SURFACE LOW TO THE NORTHERN EDGE OF THE ENVELOPE AS IT ENTERS THE GREAT LAKES. THE GFS FEATURES A WEAKER LOW...AROUND 1000 MB AT 14/00Z...WHEREAS THE OPERATIONAL MODEL CONSENSUS IS ABOUT A 995 MB LOW. THIS MAY BE...IN PART...THE REASON THAT THE GFS PRODUCES LESS SOUTHWARD PUSH ON THE TRAILING COLD FRONT. THE 12Z ECMWF/UKMET/CANADIAN CLUSTER WELL WITH RESPECT TO DEPTH OF THE SYSTEM AND SOUTHWARD PUSH OF THE COLD FRONT. ...SHORTWAVE APPROACHING THE PACIFIC NORTHWEST LATE THURSDAY... PREFERENCE: BLEND OF THE 12Z OPERATIONAL MODELS CONFIDENCE: ABOVE AVERAGE A WELL DEFINED SHORTWAVE IS FORECAST TO ROTATE AROUND THE BASE OF THE POSITIVELY TILTED LONGWAVE TROUGH IN THE GULF OF ALASKA...EJECTING TOWARD THE PACIFIC NORTHWEST COAST BY DAYS 3/4. THE 00Z CANADIAN WAS FAST AND THE 00Z UKMET SLOW. BOTH TRENDED TOWARD THE MIDDLE GROUND IN THEIR 12Z RUNS...YIELDING A STRONG MODEL CONSENSUS. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE