MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 126 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 WITH 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 00Z ECMWF/00Z GFS SOLUTIONS HERE, WHICH SPLIT THE DIFFERENCE BETWEEN THE 00Z GEFS/12Z ECMWF ENSEMBLE MEAN SOLUTIONS -- WITH 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 ON A DAY-TO-DAY BASIS, 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 STABILIZING 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