MODEL DIAGNOSTIC DISCUSSION...AMENDED NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1206 AM EST TUE JAN 21 2014 VALID JAN 21/0000 UTC THRU JAN 24/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION AND PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE ITS SHORT RANGE FORECAST. PAIR OF SYSTEMS MOVING THROUGH THE WEST WED/THU ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GFS/ECMWF COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE GUIDANCE IS AGREEABLE, AND TRENDING WEAKER ON A DAY-TO-DAY BASIS, WITH THE FIRST SHORTWAVE OF THE PAIR MOVING THROUGH THE INTERMOUNTAIN WEST WEDNESDAY/EARLY THURSDAY. ISSUES ARE LARGER WITH THE SECOND SYSTEM WHICH LEAVES THE MAIN BELT OF THE WESTERLIES AND ATTEMPTS TO CIRCUMNAVIGATE THE SOUTHERN PERIPHERY OF A CLOSED HIGH FORMING NEAR WESTERN BRITISH COLUMBIA -- SOMETIMES REFERRED TO AS ANTICYCLONIC WAVE BREAKING EVENT. THE 00Z UKMET/00Z CANADIAN ARE THE MOST RETROGRESSIVE -- WHICH CAN BE A BIAS IN THE GUIDANCE -- WHILE THE 00Z NAM IS THE FARTHEST EAST. WITH THE FORMING CLOSED HIGH OVER WESTERN BRITISH COLUMBIA, SOME RETROGRESSION IS LIKELY. PREFER THE INTERMEDIATE 12Z ECMWF/00Z GFS SOLUTIONS HERE, WHICH SPLIT THE DIFFERENCE BETWEEN THE 18Z GEFS/12Z ECMWF ENSEMBLE MEAN SOLUTIONS -- WHICH SLIGHTLY ABOVE AVERAGE CONFIDENCE DUE TO THE SYSTEM'S SLOWING PROGRESSION. SHORTWAVE APPROACHING THE GREAT LAKES FRIDAY MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE THE GUIDANCE IS IN GOOD AGREEMENT WITH THIS SYSTEM. TO DEAL WITH LINGERING DETAIL ISSUES, THE PREFERENCE IS FOR A GENERAL MODEL COMPROMISE WITH AVERAGE CONFIDENCE CONSIDERING THE SYSTEM'S PROGRESSIVE NATURE. TROUGH ALOFT AMPLIFYING OVER THE OHIO VALLEY THURSDAY LOW/ARCTIC FRONT MOVING THROUGH EASTERN US WED/EARLY THU ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE THERE HAS BEEN SOME CONVERGENCE IN THE GUIDANCE WITH THIS FEATURE, AS THE GFS HAS SHOWN SOME SLOWING. SINCE THE GUIDANCE IS REASONABLY CLOSE, THE PREFERENCE IS FOR A GENERAL MODEL COMPROMISE WITH AVERAGE CONFIDENCE CONSIDERING THE SYSTEM'S PROGRESSIVE NATURE. STRONG UPPER LEVEL SHORTWAVE MOVING THROUGH EAST TUESDAY CYCLONE MOVING THROUGH THE MID-SOUTH/SOUTHEAST TUESDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: AVERAGE THE GUIDANCE CONTINUES TO TREND STRONGER WITH THIS SYSTEM ALOFT, WHICH IS STRENGTHENING ITS RELATED SURFACE LOW AND THE SYSTEM'S OVERALL SNOWFALL POTENTIAL. THE GUIDANCE REMAINS AGREEABLE, WHICH LEADS TO A PREFERENCE FOR A GENERAL MODEL COMPROMISE WITH AVERAGE CONFIDENCE CONSIDERING THE YET-TO- BE-STABLE GUIDANCE AND THE SYSTEM'S PROGRESSIVE NATURE. SEE WPC WINTER WEATHER PRODUCTS FOR THE LATEST ON THIS SYSTEM'S WINTER WEATHER POTENTIAL. www.wpc.ncep.noaa.gov/html/model2.shtml... ROTH