MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 143 PM EST WED DEC 28 2016 VALID DEC 28/1200 UTC THRU JAN 01/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH PREFERENCES AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SHORTWAVE TROUGH AXIS EXITING FROM NEW ENGLAND TODAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW STRONG AGREEMENT WITH THIS SYSTEM FOR THE REMAINDER OF ITS TIME OVER NORTH AMERICA. ENOUGH SO FOR A GENERAL MODEL BLEND TO SUFFICE AT ABOVE AVERAGE CONFIDENCE. UPPER TROUGH AMPLIFYING FROM THE NRN PLAINS TO THE EAST COAST THROUGH THU AND ASSOCIATED DEEP NEW ENGLAND COASTAL SFC LOW DEVELOPING THU NIGHT INTO FRIDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE AS THE TRAIN OF SHORTWAVE PERTURBATIONS CONTINUE TO COMPOUND INTO A BROADER DEEPER TROF ACROSS THE EASTERN US...SMALL YET METEOROLOGICALLY SIGNIFICANT DIFFERENCES REMAIN IN THE TIMING OF THE SHORTWAVE ENERGY REACHING NEGATIVE TILT UNDER HIGHLY DIFFLUENT. THE GFS HAS BEEN THE FASTER OF THE SOLUTIONS AND LIFTS THE SYSTEM THROUGH NEW ENGLAND QUICKER THAN THE ECMWF/ECENS MEAN AND CONTINUITY HAVE BEEN SUGGESTING. THE 12Z GFS RUN REMAINS A FASTER SOLUTION LIKE ITS EARLIER RUNS BUT THERE IS A SUBTLE SHIFT TO THE WEST AND NEARER THE COAST TOO EARLY ON. THE 12Z NAM ALSO SHOWED A SLIGHTLY FASTER TRANSITION OF THE ENERGY THROUGH THE TILT LEADING TO IT BREAKING FROM THE 00Z ECMWF/CMC FAVORED CLUSTERING...IN FACT THE LOW TRACK IS QUITE SIMILAR TO THE GFS THOUGH BENDS FURTHER WEST UNDER TIGHTER ROTATIONAL INFLUENCE WITH RESPECT TO THE CENTER OF THE LARGER SCALE TROF ALONG THE ONT/QUE BORDER. THIS IS LEADING TO DECREASED CONFIDENCE IN ONE CAMP OVER THE OTHER. CONTINUITY WOULD FAVOR THE ECMWF/CMC OVER THE GFS/NAM BUT WPC PREFERENCE WILL HEDGE A BIT TO ENCOMPASS THESE SLIGHT CHANGES. SOME ADDITIONAL HI-RES GUIDANCE AND FIRST GLIMPSE AT THE 12Z UKMET ALL SUGGEST FASTER SOLUTION. THE ONLY SIGNIFICANT OUTLIER REMAINS THE 00Z UKMET WHICH IS SUFFICIENTLY SLOWER THAN EVEN THE 00Z ECMWF/CMC SOLUTIONS AND AS SUCH IS ABLE TO GENERATE THE DEEPEST SURFACE REFLECTION ACROSS NH/ME AND THEREFORE LINGERS COMPOUNDING QPF/SNOW TOTALS. ALL IN ALL...A NON-UKMET (00Z) BLEND IS PREFERRED BUT WILL CONTINUE TO WEIGHT THE PREFERENCE SLIGHTLY MORE TO GFS/NAM GIVEN THE TRENDS NOTED IN NEWEST GUIDANCE INCLUDING HI-RES SOLUTIONS. CONFIDENCE IS REDUCED TO AVERAGE GIVEN THE LARGER BLEND WASHING OUT SOME IMPORTANT DETAIL. 19Z UPDATE: A SLIGHTLY FASTER ECMWF/CMC AND UKMET ALL BEGIN TO PRESENT A SIMILAR EVOLUTION EVEN IN TIMING TOWARD THE 12Z GFS THOUGH ALL REMAIN SLOWER THAN GFS EXACTLY. THIS ADJUSTMENT BRINGS BACK CONFIDENCE IN A MORE COMMON SOLUTION. AS SUCH A GENERAL MODEL BLEND IS PREFERRED WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE. MID-LEVEL LOW OFF OF SOUTHWEST U.S. COAST APPROACHING CALIFORNIA BY END OF WEEK ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF/UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 00Z CMC IS A CLEAR OUTLIER BEING A BIT WEAKER OVERALL AND ALSO LIFTING NORTHEAST A BIT EARLIER THAN THE REST OF THE GUIDANCE. AS SUCH THE SOLUTION BY DAY THREE IS ALMOST 3-4 DEGREES FURTHER EAST THAN OTHER GUIDANCE. THE 12Z NAM SHOWS SOME OF ITS TYPICAL BIAS IN PRODUCING A DEEP/CONSOLIDATED VORT CENTER THAT DOES NOT BREAK DOWN UNDER THE SHEARING FORCES AS IT SHOULD (LIKE THE OTHER GUIDANCE DOES, EVEN THE CMC). THIS KEEPS THE NAM FURTHER SOUTH AND STRONG MOVING THROUGH S CA INTO AZ BY SAT. THE 12Z GFS SHOWING A BIT LESS INTERACTION WITH THE SLOWER DESCENDING TROF REMAINS A BIT FURTHER SOUTH AND ROBUST CROSSING OUT OF NM INTO TX BY LATE SAT JUXTAPOSED BY THE 00Z UKMET WHICH IS A BIT FLATTER AND FASTER; THE 00Z ECMWF SPLITS THE DIFFERENCE. THE DIFFERENCES ARE FAIRLY MILD AND AS SUCH WILL FAVOR A 12Z GFS AND 00Z UKMET/ECMWF BLEND (WEIGHTING TOWARD THE MIDDLE...ECMWF). CONFIDENCE IS SLIGHTLY ABOVE AVERAGE. 19Z UPDATE: WHILE THE CMC DID TREND A BIT STRONGER AND SLOWER IT CONTINUES TO BE THE WEAKEST AND FASTEST SHEARING INTO THE WESTERLY FLOW ACROSS THE SOUTHWEST. THE UKMET AND ECMWF BOTH ADJUSTED A BIT FURTHER SOUTH AND WEAKER CLOSER TO THE 12Z GFS HOWEVER BOTH SHOW THEIR BIAS TOWARD THE END OF THE PERIOD; UKMET A BIT FAST AND ECMWF A BIT SLOW. STILL THOSE DIFFERENCES ARE MINOR TO KEEP A GFS/ECMWF/UKMET BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. LEAD SHORTWAVE ENERGY OF LARGER SCALE TROF REACHES SW BC BY EARLY THURSDAY TREKKING ACROSS SW CANADA INTO THE GREAT LAKES BY SATURDAY EVENING WITH ACCOMPANYING SURFACE LOW ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE MODELS HAVE BECOME MORE SOLIDLY ALIGNED WITH THE SHORTWAVE AND ASSOCIATED SURFACE LOW REACHING THE BC EARLY THURSDAY...AS THE WAVE CROSSES THE CANADIAN ROCKIES A BIT OF SPREAD IS INCURRED TO THE SYSTEM; MAINLY THE CMC BECOMING SLOWER AND FURTHER SOUTH. OTHERWISE THE SPREAD IS MILD WITH MODERATELY TIGHT SURFACE LOW CLUSTERING NOTED IN THE ENSEMBLE SUITE EVEN THROUGH THE GREAT LAKES. BY THE VERY END OF SAT...THE 00Z UKMET AND 12Z NAM ARE A BIT FLATTER AND SHEARED NORTHEAST THAN THE ECMWF/GFS BUT THIS APPEARS MINOR AND WELL WITHIN THE ENSEMBLE SPREAD OF POSSIBILITIES. AS SUCH A NON-CMC BLEND CONTINUES TO REMAIN WPC PREFERENCE AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. 19Z UPDATE: SMALL ADJUSTMENTS FOR THE NON-NCEP 12Z RUNS...ALL FAVORABLY TOWARD CONSENSUS. THE 12Z CMC HOWEVER STILL PREFERS TO EJECT THE WAVE OUT OF THE CANADIAN ROCKIES A BIT FURTHER SOUTH AND KEEPS THE LOW TRACK SOUTH OF THE REMAINING CONSENSUS THROUGH SUN. THE ECMWF/GFS REMAIN TIGHTEST CLUSTERED TO THE MIDDLE OF THE ENSEMBLE AND WILL CONTINUE TO FAVOR HIGHER WEIGHTING TO THOSE MEMBERS WITHIN A NON-CMC BLEND. REMAINING PORTION OF POSITIVELY TILTED UPPER TROUGH ENTERING NORTHWEST FRI AND POTENTIALLY CLOSING OFF ACROSS CA/GREAT BASIN SAT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF/12Z NAM CONFIDENCE: SLIGHTLY BELOW AVERAGE LOW PREDICTABILITY SETUP AS FLOW SLACKENS IN FAVOR OF THE DEEP CUT-OFF SW AND THE NORTHERN PORTION OF THE WAVE ACCELERATING ACROSS S CANADA (SEE SECTION ABOVE)...AS SUCH THERE REMAINS FAIRLY LARGE ENSEMBLE SPREAD KEEPING CONFIDENCE BELOW AVERAGE. YET THERE IS SOME HOPE TOWARD A MORE COMMON SOLUTION OF A CLOSED LOW DEVELOPING NEAR/ALONG THE CA COAST BY LATE SAT. TO BE GIVEN WEAK FLOW BETWEEN STREAMS...TIMING IS THE MAIN DRIVER TO THE SPREAD DIFFERENCE. AS SUCH WILL CONTINUE TO FAVOR A MIDDLE GROUND SOLUTION WHICH CONTINUES TO BE PRESENTED BY THE 00Z ECENS MEAN WHICH HAS BEEN VERY CONSISTENT OVER THE LAST 4-5 CYCLES TOO PROVIDING SOME CONFIDENCE. THE OPERATIONAL 00Z ECMWF SHOWS SOME OF ITS NEGATIVE BIAS BY THE END OF DAY 3 IN COMPARISON TO THE ECENS MEAN; BEING VERY TIGHTLY WOUND AND A BIT SLOW/SOUTH. YET THE 00Z RUN CONTINUES TO BE WELL TIMED AS WELL. THE 12Z NAM ALSO APPEARS GENERALLY FAVORABLE TO THE ECENS MEAN JUST A BIT DEEP INITIALLY ALLOWING A FURTHER INLAND TRACK ALONG THE SPINE OF THE SIERRAS BUT IS LIKEWISE QUITE FAVORABLE TO THE ECENS MEAN. IF THE ECMWF IS WOUND UP THE 00Z UKMET TAKES IT EVEN FURTHER BUT IS ALSO SHOWING SOME OF ITS BIAS TOWARD A FASTER SOLUTION...SO TWO STRIKES AGAINST IT...THOUGH IT REMAINS A BIT MORE PREFERABLE TO THE GFS OR CMC. THE 00Z CMC REMAINS VERY FAST GIVEN THE WEAKER DOWNSTREAM SHORTWAVE. THE 12Z GFS HAS TRENDED POSITIVELY TO THE OTHER SOLUTIONS NOW SUGGESTING A MID-LEVEL CLOSED LOW BUT CONTINUES TO BE THE SLOWEST AND MOST INCONSISTENT GUIDANCE WITH THIS SYSTEM. A BLEND OF THE 12Z NAM AND 00Z ECMWF MAY BE THE BEST REPRESENTATION OF THE PREFERRED ECENS MEAN. CONFIDENCE IS SLIGHTLY BELOW AVERAGE IN THIS BLEND. 19Z UPDATE: 12Z NON-NCEP DETERMINISTIC RUNS SHOW GREATER CLUSTERING AND WHILE THE ECMWF AND UKMET CONTINUE TO BE VERY ROBUST AND STRONG THEY ALSO HAVE TEMPERED A BIT TOWARD THE FAVORED ECENS. THE UKMET IS ALSO A BIT SLOWER ALONG WITH THE CMC. THE 12Z CMC HOWEVER IS MORE LIKE THE NAM BEING A BIT FURTHER INLAND THAN THE ECMWF/UKMET. STILL THIS IS FAIRLY GOOD AGREEMENT THOUGH THE SPREAD IS MODERATE TO LARGE BUT SHRINKING TO HAVE SOME INCREASED CONFIDENCE IN THE 00Z ECENS MEAN. ONLY THE GFS DOES NOT COMPLY WITH THIS THINKING YET...AND AS SUCH WILL SUPPORT A NON-GFS BLEND AT SLIGHTLY BELOW AVERAGE CONFIDENCE. DESCENDING SHORTWAVE ENERGY ALONG BRITISH COLUMBIA INTO THE PACIFIC NORTHWEST BY THE END OF THE FORECAST PERIOD ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-GFS BLEND CONFIDENCE: AVERAGE THE NEXT SHORTWAVE COMES OUT OF THE GULF OF ALASKA LATE FRIDAY/EARLY SATURDAY AND HUGS THE COAST AS IT APPROACHES THE PACIFIC NW US BY SAT EVENING. THE 12Z GFS CONTINUES TO TREND MUCH FASTER THAN PRIOR RUNS TOWARD THE FASTER ECMWF/ECENS MEMBERS SOLUTIONS. THIS IS MUCH LIKE THE OVERALL TREND NOTED IN THE LAST 3-4 CYCLES IN THE ENSEMBLE SPAGHETTI ANALYSIS. STILL THE 12Z GFS REMAINS THE SLOWEST THE MAIN DIFFERENCE SEEMS TO BE PLACEMENT OF THE CORE OF THE SHORTWAVE...INSIDE THE COASTAL RANGE LIKE THE ECMWF/CMC OR WEST LIKE THE MOST AMPLIFIED 12Z NAM. TRACK/PLACEMENT OF THE WAVE SEEMS MORE FAVORABLE TO THE ECMWF/CMC BUT GIVEN THE TIMING/STRENGTH OF THE WAVE IS FAIRLY AGREED UPON BETWEEN THE NAM/UKMET/ECMWF/CMC TOWARD THE ENSEMBLE MEAN WILL FAVOR A NON-GFS SOLUTION (AS IT REMAINS A BIT TOO SLOW...THOUGH GETTING "BETTER"). WITH INCREASING MODEL AGREEMENT CONFIDENCE IN A NON-GFS BLEND IS AVERAGE. 19Z UPDATE: ALL THREE 12Z NON-NCEP SOLUTIONS TRENDED A BIT FASTER LIKE THE 12Z NAM/GFS. ADDITIONALLY BOTH THE ECMWF AND CMC TRENDED TOWARD AN WESTERN MORE SHARP WAVE AMPLITUDE PROVIDING FURTHER AGREEMENT WITH THE UKMET/NAM SET UP AS WELL. STILL THERE REMAINS SMALL DIFFERENCES IN TIMING TO HAVE MUCH HIGHER CONFIDENCE AND MODELS DO CONTINUE TO ADJUST FASTER OVER THE LAST FEW RUNS TO HAVE TREMENDOUS CONFIDENCE; AS SUCH WILL KEEP WITH INITIAL PREFERENCE OF NON-GFS AND AVERAGE CONFIDENCE FOR THIS WAVE AT THIS POINT. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA