MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1116 PM EST SUN JAN 22 2017 VALID JAN 23/0000 UTC THRU JAN 26/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ CLOSED LOW ACROSS THE SOUTHEAST CURRENTLY WITH STRONG SURFACE LOW. SURFACE LOW REFORMS OFF DELMARVA COAST TUESDAY BEFORE LIFTING INTO NEW ENGLAND LATE TUE/WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF/UKMET BLEND (AT THE SURFACE) THROUGH 24/12Z NON-NAM THEREAFTER CONFIDENCE: SLIGHTLY ABOVE AVERAGE EARLY IN THE FORECAST PERIOD...EVEN THOUGH THERE IS VERY TIGHT CONSENSUS THROUGH THE MIDDLE AND UPPER LEVELS THERE IS A SPLIT IN TIGHT CLUSTERING WITH RESPECT TO THE SURFACE WAVE IN THE ENSEMBLE SUITE. THE 12Z ECMWF PAIRED WITH THE UKMET SUPPORT A DEEPER SURFACE LOW TRACKING ACROSS THE SOUTHERN APPALACHIANS THROUGH THE CAROLINAS BEFORE RE-CENTERING OFF THE DELMARVA COAST MIDDAY TUES AT THE TRIPLE POINT COMING BACK INTO OVERALL MODEL AGREEMENT. THE 00Z GFS/NAM SHOW A MUCH WEAKER AND FURTHER NORTH OCCLUDED SURFACE LOW MOVING ALONG THE NC/VA BORDER BEFORE THE REDEVELOPMENT ON MIDDAY TUESDAY. CURRENT OBSERVATIONS AND ONGOING LATENT HEAT RELEASE OVER N GA/AL WITH THE MAIN MID-LEVEL SHORTWAVE TROF TO SWING THROUGH LATER TONIGHT SUGGEST THE DEEPER OCCLUDED LOW OF THE ECMWF/UKMET BLEND. AFTER 24/12Z...MODEL AGREEMENT IS MUCH STRONGER WITH ONLY THE 00Z NAM BREAKING A STRONGER AND DEEPER SOUTHEAST ELONGATION OF THE UPPER TROF AND LEADING TO THE SURFACE REDEVELOPMENT WELL SOUTHEAST AND OUT OF CONTINUITY AND OVERALL AGREEMENT. AS SUCH A 12Z UKMET/ECMWF BLEND IS SUPPORTED AT THE SURFACE UP THROUGH 24/12Z...WITH A NON-NAM BLEND THEREAFTER. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE THROUGHOUT. LONGWAVE TROUGH OVER THE WEST COAST BY MON MORNING DOWNSTREAM SURFACE LOW INTO THE PLAINS FOR TUE LIFTING INTO THE GREAT LAKES WED. ELONGATED POSITIVE TILT TROF MOVING THROUGH CENTRAL US WED INTO EASTERN THIRD OF US BY THURS. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND ALONG THE WEST COAST 00Z GFS AND 12Z/ECMWF/UKMET FROM THE ROCKIES TO GREAT LAKES CONFIDENCE: SLIGHTLY ABOVE AVERAGE DETERMINISTIC AND ENSEMBLE SOLUTIONS SEEM TO HAVE COME TO A CONSENSUS WITH RESPECT TO THE REMAINING EVOLUTION OF THE DEEP INNER CORE TO THE UPPER LOW AND SURFACE REFLECTION OFF THE OR/WA COAST EVEN AS THE WEAKENING WAVE DESCENDS TOWARD THE CA COAST TUESDAY. THE 12Z CMC BECOMES A BIT FASTER OVERALL...BUT GIVEN DOWNSTREAM ISSUES WITH THE CMC IT WOULD BE OUT OF PREFERENCE AWAY. AS THE MAIN LONGWAVE TROF CONTINUES TO PROGRESS THROUGH THE WESTERN US MONDAY INTO EARLY TUES THERE REMAINS SOME MODEL DISAGREEMENT IN TIMING OF WHEN AND HOW FAR EAST THE NEW INNER CORE OF THE UPPER LOW AND ASSOCIATED BROAD SURFACE REFLECTION DEVELOPING IN THE PLAINS. THE 00Z NAM CONTINUES TO BE A BIT MORE AGGRESSIVE IN REFORMING THE CLOSED UPPER LOW WHILE ALSO TRANSLATING THE SURFACE LOW FASTER THROUGH THE WESTERN MIDWEST AND GREAT LAKES BY WED EVENING. THE 12Z CMC IS MUCH TOO SLOW AS IT HAS BEEN. THE 12Z ECMWF/UKMET CONTINUE TO BE MOST CENTRAL TO THE ENSEMBLE SPREAD WITH FAIRLY GOOD CONTINUITY OVERALL. THE 00Z GFS WHILE STILL BIT A BIT FASTER INITIALLY TO CLOSE OFF THE MID-LEVEL LOW OUT OF THE ROCKIES IS A BIT BROADER BUT ALSO A SLOWER THAN PRIOR GFS RUNS COMING TOWARD THE ECMWF/UKMET TIMING. GIVEN THE SPREAD WAS SMALL BETWEEN THE FASTER NAM/GFS BEFORE AND THE GFS HAS SLOWED...INCLUSION OF THE 00Z GFS WITH THE 12Z ECMWF/UKMET IS NOW THE PREFERENCE ACROSS THE EASTERN HALF OF THE LONGWAVE TROF (CENTRAL PLAINS TO GREAT LAKES). HIGHLY AMPLIFIED SHORTWAVE APPROACHING WEST COAST LATE WED/EARLY THURSDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z GFS AND 12Z ECMWF/CMC BLEND CONFIDENCE: AVERAGE IN THE WAKE OF THE BROAD LONG WAVE TROF...A HIGHLY AMPLIFIED SHORTWAVE RIDGE PUMPS UP ALONG THE NORTHWEST COAST INTO WED...WITH SOME SHORTWAVE ENERGY TRYING TO UNDERCUT IT ACROSS THE CENTRAL WEST COAST INTO THURSDAY WITH AN ASSOCIATED NARROW/WEAK SURFACE FRONT. THE UKMET IS A BIT STRONGER AND FASTER WITH THE BASE OF THE TROF. THE 00Z NAM IS GENERALLY ABOVE TOO BROAD AS THE WAVE BREAKS DOWN INTO N CA...TO BE FULLY PREFERRED AS WELL. THE REMAINING 00Z GFS AND 12Z ECMWF/CMC SHOW SOME MODERATE SPREAD BUT GIVEN THE OVERALL PATTERN OF NARROW BUT HIGHLY AMPLIFIED WAVE PATTERN BY DAY 3...THIS IS GOOD AGREEMENT AS A WHOLE TO SUPPORT THE BLEND AT AVERAGE CONFIDENCE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA