MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 131 PM EST SAT DEC 03 2016 VALID DEC 03/1200 UTC THRU DEC 07/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SHORTWAVE AMPLIFYING INTO A CLOSED LOW ACROSS NORTHERN MEXICO SAT/SUN LIFTS INTO TX BY MON SPURRING SURFACE LOW DEVELOPMENT IN WESTERN GULF MON LIFTING INTO LOWER MS VALLEY TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z ECMWF/UKMET/CMC BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE SPREAD CONTINUES TO BE PERSISTENT MAINLY IN TIMING ISSUES THAT APPEAR TO BE RELATED TO THE CROSSING OUT OF THE LESSER DATA NETWORK OF NORTHERN MEXICO AND SOME TIMING DUE TO STRETCHING CROSSING THE N SIERRA MADRE ORIENTAL. THE 12Z NAM IS VERY QUICK TO DEPART FASTER THAN THE SPREAD NOT WOBBLING AT THE BASE OF THE TROF BEFORE THE TURN BACK NORTHEAST. THIS SHOWS ONLY LIMITED SUPPORT FROM VERY FAST ECENS MEMBERS WHICH HAVE HAD A NOTORIOUS FAST BIAS THROUGHOUT THE LAST WEEK WITH THIS SYSTEM. THE 00Z ECMWF IS ALMOST AN EXTREME SLOW MEMBER OF THE 00Z ECENS MEAN BUT HAS A VERY FAVORABLE CENTRAL LOCATION AS WELL AS KEEPING WITH WPC PREFERENCE OVER THE PAST DAY OR SO. THE 00Z UKMET IS MATCHED WELL WITH THIS SOLUTION AS WELL TO BUILD FURTHER CONFIDENCE. ALL OF THIS AS THE GFS HAS BEEN SLOWING IN TREND WITH TIME COUNTER TO WPC PREFERENCE. THE 12Z GFS KEEPS WITH THE GFS TREND EXITING MX A BIT SLOWER AND THEREFORE TRACKS EASTWARD FURTHER SOUTH THAN CONTINUITY AND PREFERENCE. HOWEVER BY DAY 3...THE GFS SHOWS BETTER TIMING WHILE RETAINING SOME STRENGTH IN THE WAVE AS IT WEAKENS/LIFTS THROUGH THE APPALACHIANS. THIS IS LIKELY WHY THE AGREEMENT WITH THE COASTAL SURFACE LOW IS MORE IN LINE WITH THE ECMWF AND MAY BE WORTH BLENDING FULLY IN AREAS EAST OF THE APPALACHIANS. THE 00Z CMC IS LIKE THE GFS A BIT SLOWER INITIALLY. AS THE WAVE LIFTS AND WEAKENS THROUGH THE LOWER MS VALLEY...THE CMC BREAKS FROM THE GFS AND RAPIDLY WEAKENS OUT THE WAVE. ALL CONSIDERED WILL FAVOR THE 00Z ECMWF/UKMET BLEND OVERALL WITH INCLUSION OF THE 12Z GFS ALONG THE EAST COAST ONLY. CONFIDENCE REMAINS AVERAGE IN THIS BLEND. 19Z UPDATE: SMALL CHANGES IN THE INITIAL PREFERENCE; 12Z ECMWF SLIGHTLY SLOWER AND 12Z UKMET A BIT SHALLOWER, KEEP HIGHER CONFIDENCE IS THIS MIDDLE GROUND SOLUTION. THE 12Z CMC TRENDED TOWARD BETTER AGREEMENT IN TIMING WITH BOTH THOUGH JUST A BIT SHALLOWER THAN THE UKMET. STILL A NON-NCEP BLEND IS PREFERABLE AT THIS POINT. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE GIVEN ADDITIONAL AGREEMENT FROM THE CMC BUT MORE IMPORTANTLY CONTINUITY WITH LAST 2-3 RUNS OF THE UKMET/ECMWF. SHORTWAVE CROSSING SOUTHWEST NORTHERN PLAINS SAT...WESTERN GREAT LAKES SUNDAY...NEW ENGLAND MON ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE MODELS HAVE CONTINUED TO SHOW MODERATE AGREEMENT OVERALL THOUGH TIMING IS BETTER ALIGNED THAN SPECIFIC DEPTH. THE 12Z NAM HAS SHIFTED TOWARD THE BETTER ALIGNMENT IN TIMING/DEPTH OF THE CONTINUITY THAT IS REPRESENTED BY THE 00Z ECMWF/UKMET/GFS. THE 12Z GFS HAS A SIMILAR TIMING/EVOLUTION TO THE 00Z; KEEPING GOOD CONFIDENCE IN THIS SET UP. ONLY THE 00Z CMC HAS DEPARTING MASS DIFFERENCES AND WHILE THE TIMING IS FAIRLY GOOD THE DOWNSTREAM RIDGE A BIT WEAKER ALLOWING THE CMC TO SLIDE/SHEAR OUT ACROSS THE NORTHEAST A BIT QUICKER. AS SUCH A NON-CMC BLEND IS PREFERRED. DIFFERENCES IN DEPTH LEAD TO SOME REDUCTION IN THE HIGHEST CONFIDENCE BUT STILL IS SLIGHTLY ABOVE AVERAGE. 19Z UPDATE: THE 12Z CMC HAS SHIFTED TOWARD BETTER OVERALL CONSENSUS OF THIS WAVE...AS SUCH A GENERAL MODEL BLEND IS PREFERRED THOUGH SOME MINOR DEPTH ISSUES REMAIN TO NOT BE FULLY CONFIDENT (ABOVE AVERAGE)...SO CONFIDENCE IS SLIGHTLY ABOVE AVERAGE. SHORTWAVE CROSSING THE PACIFIC NORTHWEST AND NORTHERN ROCKIES SUN AND THEN NORTHERN PLAINS BY MONDAY/UPPER MS VALLEY MON NIGHT WITH DEEPENING SURFACE LOW MON/TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z/00Z ECMWF BLEND CONFIDENCE: AVERAGE THE MODELS ARE BECOMING BETTER ALIGNED AS THE MAIN WAVE CROSSES THROUGH THE NORTHERN CANADIAN ROCKIES WITH A TRAILING SHORTWAVE ENTERING VANCOUVER ISLAND SUNDAY MORNING. THE MAIN WAVE SETS UP ACROSS THE NORTHERN PRAIRIE PROVIDENCES AND HELPS TO SWING THE SHORTWAVE AND ASSOCIATED JET STREAK THROUGH THE NORTHERN US ROCKIES. THE 12Z GFS CONTINUES TO BE SLIGHTLY FASTER AND A BIT MORE AMPLIFIED EXITING MT/WY AND ROUNDS THE SHARP BASE WITH TIGHT HEIGHT PACKING ENOUGH TO SUPPORT RAPID DEEPENING WITH A STRONG DEEP LOW ACROSS THE NORTHERN RED RIVER VALLEY EARLY TUESDAY MORNING. THE 00Z ECMWF FOLLOWED CLOSELY BY THE 00Z UKMET AND 12Z NAM ARE CLOSE BEHIND BUT GIVEN THE SLIGHTLY DELAYED ARRIVAL THE SPIN UP IS A BIT LESS ROBUST WHILE SHOWING SIMILAR EVOLUTIONARY PATH/TRACK. THE 00Z UKMET'S UPPER LOW AND KICKER S/W WERE A BIT DELAYED COMPARED TO THE NAM/ECMWF WHICH FURTHER SLOWS THE DEVELOPMENT. THE 00Z CMC IS WELL OUT OF PHASE/BROADER WEAKER IN CANADA AND WELL SLOWER IN THE NORTHERN PLAINS...WITH A VERY WEAK SURFACE LOW STAYING WELL SOUTH. WHILE THE GFS MAY BE A SHADE TOO FAST THERE IS MORE ENSEMBLE SUPPORT AND STRONGER PACIFIC FLOW ALOFT TO NOT DISMISS THE POSSIBILITY. AS SUCH WILL SUPPORT A NON-CMC BLEND WITH HIGHER WEIGHTING TOWARD THE 00Z ECMWF. GIVEN THE SPREAD IN POTENTIAL IMPACT/DEPTH OF THE LOW CONFIDENCE IS A BIT LOW BUT AVERAGE OVERALL. 19Z UPDATE: FURTHER SLOWING IN TIMING OF THE ECMWF MAKES DEEP SOLUTION OF THE 12Z GFS A BIT TOO MUCH TO SUGGEST MAY OCCUR. THIS AS THE UKMET IS SLOWER SLIGHTLY AND THE 12Z CMC TRENDED FASTER TOWARD BETTER TIMING/STRENGTH OF THE NAM AND UKMET. STILL WOULD PREFER THE ECMWF AS THE MIDDLE GROUND. AS SUCH PREFERENCE IS A 12Z/00Z ECMWF BLEND AT AVERAGE CONFIDENCE. LOW DEVELOPING OVER THE NORTHEAST PACIFIC AND MOVING JUST OFF VANCOUVER ISLAND 12Z MON AND INTO GREAT BASIN BY TUESDAY NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE GULF OF ALASKA SHORTWAVE/UPPER LOW UNDER THE INFLUENCE OF EXPANDING BROAD GLOBAL SCALE TROF ACROSS NW CANADA BEGINS TO SHEAR ALONG THE BRITISH COLUMBIA COAST AND SLIDE INTO THE US PACIFIC NW BEFORE SETTLING ACROSS THE GREAT BASIN ON TUESDAY AS BROADER LESS AMPLIFIED WAVE. GIVEN ISSUES DOWNSTREAM IN TIMING...THE 00Z CMC HAS A SLIGHTLY DIFFERENT ORIENTATION OF THE WAVE BUT IN A GENERAL SENSE THE TIMING/DEPTH/PLACEMENT OF THE WAVE IS IN GOOD AGREEMENT AND THERE IS SOLID ENSEMBLE SUPPORT TO SUGGEST A GENERAL MODEL BLEND AS PREFERENCE. CONFIDENCE IS SLIGHTLY ABOVE AVERAGE. 19Z UPDATE: LITTLE DIFFERENCES IN THE ECMWF/UKMET WHILE THE 12Z CMC BEING FASTER DOWNSTREAM ALLOWS FOR TIGHTER MODEL AGREEMENT FOR THE WAVE TO KEEP A GENERAL MODEL BLEND. SPREAD IS MODERATE ENOUGH BY DAY 3 (ESPECIALLY WITH SPARSE DATA NETWORK UPSTREAM) THAT A CONFIDENCE IN THIS BLEND IS SLIGHTLY ABOVE AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA