MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 153 PM EST WED JAN 15 2014 VALID JAN 15/1200 UTC THRU JAN 19/0000 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. ============================================== ...SHORTWAVE LIFTING OUT OF FLORIDA BEGINNING TONIGHT... PREFERENCE: BLEND OF 12Z NAM/ECMWF/UKMET...DROPPING THE NAM AFTER 18/00Z CONFIDENCE: SLIGHTLY BELOW AVERAGE TWO SURFACE LOW CENTERS ARE FORECAST ALONG A SLOW MOVING FRONTAL ZONE IN THE WESTERN ATLANTIC. THE LOW MOST CLOSELY ASSOCIATED WITH THIS SHORTWAVE LIFTING FROM FLORIDA...WILL GRADUALLY DEVELOP OFFSHORE OF THE CAROLINAS TONIGHT AND THURSDAY. THE LOW IS FORECAST TO REMAIN RELATIVELY WEAK AND SMALL SCALE...AS THE MID LEVEL SHORTWAVE DE-AMPLIFIES. THE NAM AND ECMWF SHOW SLIGHTLY MORE ROBUST SURFACE LOW DEVELOPMENT EARLY ON...WHEN THE SHORTWAVE STILL HAS SOME PUNCH TO IT. THE UKMET SUPPORTS THESE MODELS WITH SIMILAR TIMING. WE CONTINUE TO FAVOR THE NAM/ECMWF SOLUTIONS...WHEREAS THE 12Z GFS AND CANADIAN ARE SOMEWHAT WEAKER AND THEREFORE FASTER. CONFIDENCE IN THE DETAILS IS BELOW AVERAGE...HOWEVER...GIVEN THE SMALL SCALE NATURE OF THE DISTURBANCE AND WEAK SURFACE REFLECTION. ...SYSTEM DIVING THROUGH THE MIDWEST THURSDAY AND REACHING THE EAST COAST SATURDAY... PREFERENCE: BLEND OF 12Z NAM/ECMWF/CANADIAN CONFIDENCE: AVERAGE THIS SYSTEM WILL SWING ANOTHER SLUG OF ARCTIC AIR DOWN THROUGH THE EASTERN U.S...WHILE LOW PRESSURE WEAKENS OVER THE GREAT LAKES AND HANDS OFF TO NEW COASTAL DEVELOPMENT SATURDAY WELL OFFSHORE OF THE MID ATLANTIC. THE GFS/GEFS IS MOVING THE UPPER TROUGH MORE QUICKLY EASTWARD THAN THE ECMWF AND ITS ENSEMBLE. THIS DIFFERENCE APPEARS SYSTEMATIC...AS IT SHOWS UP IN CONSECUTIVE RUNS AND WHEN MEASURED ACROSS ALL THE ENSEMBLE MEMBERS. THE SPREAD IS NARROWING...HOWEVER...AS THE 12Z GFS DID TREND A LITTLE SLOWER AND THE 12Z ECMWF A LITTLE FASTER. GIVEN THE GFS TENDENCY TO BE TOO FAST...AND THE AVAILABILITY OF COLD AIR TO CAUSE THE TROUGH TO DIG MORE SHARPLY/SLOWER...WE WILL CONTINUE TO LEAN TOWARD AN ECMWF-LIKE SOLUTION. THE ECMWF TRENDING FASTER BRINGS IT CLOSER TO THE 12Z NAM...ALLOWING US TO INCLUDE THE NAM IN OUR PREFERENCE. THE CANADIAN ALSO IMPROVED UPON ITS FORECAST WHICH HAD EARLIER BEEN TOO SLOW WITH THE 850 MB COLD DOME. ...SECOND SHORTWAVE DIVING THROUGH THE MIDWEST SATURDAY... PREFERENCE: BLEND OF 12Z NAM/ECMWF/CANADIAN CONFIDENCE: AVERAGE A SURFACE LOW ASSOCIATED WITH THIS WAVE WILL TRACK FROM SASKATCHEWAN AT 18/00Z TO ILLINOIS AT 19/00Z. THE OPERATIONAL MODELS ARE CLUSTERING FAIRLY WELL...AND THE GFS DID SLOW DOWN SUBSTANTIALLY...JOINING THE GROWING CONSENSUS THROUGH DAY 2. ON DAY 3 THE GFS AGAIN BECOMES FASTER THAN CONSENSUS...AND THE UKMET SOLUTION WAS SOMEWHAT WEAKLY DEFINED AT THE SURFACE. ...SHORTWAVE SNEAKING THROUGH THE WEST COAST RIDGE SATURDAY... PREFERENCE: BLEND OF 12Z GFS/ECMWF/UKMET CONFIDENCE: AVERAGE THE HIGH AMPLITUDE MEAN RIDGE OVER WESTERN NORTH AMERICA IS LIKELY TO REMAIN INTACT WELL INTO THE MEDIUM RANGE...BUT ONE WEAK SHORTWAVE TROUGH IS FORECAST TO MOVE THROUGH THE RIDGE ON DAY 3. THE MODELS SHOW A GOOD DEAL OF AGREEMENT. FOR OUR PREFERENCE WE OMIT THE NAM WHICH WAS OUT OF PHASE WITH THE CONSENSUS VERY EARLY IN THE FORECAST OVER THE PACIFIC. WE ALSO OMIT THE CANADIAN WHICH KEEPS A MORE PRONOUNCED DISTURBANCE AT THE BASE OF THE TROUGH...BRUSHING WASHINGTON. TIMING IN THE CANADIAN IS ONLY SLIGHTLY SLOW...BUT THE STRENGTH OF THE EMBEDDED DISTURBANCE HAS LITTLE ENSEMBLE SUPPORT. www.wpc.ncep.noaa.gov/html/model2.shtml... BURKE