MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 205 PM EST SAT FEB 27 2016 VALID FEB 27/1200 UTC THRU MAR 02/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH PREFERENCES/CONFIDENCE LEVELS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SHORTWAVE AND ASSOCIATED STRONG SURFACE REFLECTION NEAR HUDSON BAY DRAPES A COLD FRONT THROUGH THE NORTHERN GREAT LAKES LATE SAT AND INTO NEW ENGLAND SUNDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE CONFIDENCE MODEL GUIDANCE HAS BECOME QUITE TIGHTLY AGREED UPON THROUGHOUT THE SYSTEM AS A WHOLE...AND WITH A BETTER AGREEMENT UPSTREAM WITH THE NEXT SYSTEM...THE ORIENTATION OF THE FRONT MOVING THROUGH NEW ENGLAND IS ALSO STRONG ENOUGH TO SUPPORT AN OPERATIONAL MODEL BLEND AT HIGHEST CONFIDENCE. WAVE MOVING INTO THE ROCKIES TODAY WITH SURFACE REFLECTION IN ALBERTA THAT WILL TRANSVERSE THE NORTHERN PLAINS SAT/SUN; GREAT LAKES BY SUN/MON AND N NEW ENGLAND MONDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: OPERATIONAL MODEL BLEND PRIOR 29/00Z 12Z ECMWF/CMC BLEND AFTERWARD CONFIDENCE: ABOVE AVERAGE PRIOR TO 29/00Z...SLIGHTLY ABOVE AFTER STRONGER MODEL CONVERGENCE WITH MOST RECENT CYCLES WITH RESPECT TO THE 00Z ENSEMBLE SUITE...WITH STRONG CLUSTERING WITHIN THE ENSEMBLE SURFACE LOW CLUSTER. THOUGH THERE IS A BIT OF SPREAD AS THE NORTHERN AND SOUTHERN PORTIONS OF THE WAVE MERGE ACROSS THE NORTHERN PLAINS AT 28/00Z AND CONSOLIDATE THE STREAMS/SURFACE REFLECTION...AND ONCE SETTLED BECOMES TIGHTLY CLUSTERED TROUGH THE GREAT LAKES. AFTER ABOUT 29/00Z MODELS BEGIN TO SPREAD ALOFT DUE TO INTERACTIONS WITH UPSTREAM ENERGY...THE 00Z ECMWF SLOWS AND LAGS ON THE SOUTHERN SIDE OF THE CLUSTER AWAY FROM THE WELL CLUSTERED 00Z ECENS MEAN/06Z GEFS MEAN/09Z SREF...THE 12Z NAM IS A SHADE FASTER IN THE LOWER LEVELS WHILE THE 12Z GFS "FEELING" A FASTER NORTHERN STREAM SHORTWAVE IS FASTER WITH THE WAVE AS A WHOLE AND IT DEEPENS THE SURFACE WAVE MUCH MORE THAN THE OTHERWISE SIMILAR STRENGTH/DEPTH WITH THE REST OF THE GUIDANCE. AT THIS POINT THE 00Z UKMET/CMC ARE BEST LOCATED IN POSITION/STRENGTH TO REPRESENT THE MEANS. OVERALL AN OPERATIONAL MODEL BLEND IS PREFERRED AT ABOVE AVERAGE CONFIDENCE UNTIL 29/00Z WHEN A CMC/UKMET BLEND WOULD BE BETTER REPRESENT THE MEANS AT SLIGHTLY ABOVE AVERAGE. 19Z UPDATE: A SLIGHTLY FASTER 12Z CMC/ECMWF ACROSS NEW ENGLAND MATCHES BETTER TOWARD THE OLDER 00Z ECENS MEAN AND 06Z GEFS...HOWEVER THE 12Z GEFS UNSURPRISINGLY SHIFTED TOWARD A DEEPER SOLUTION NEAR THE 12Z GFS AFTER 29/12Z...WHICH WAS ALSO SUPPORTED BY A STRONGER/NORTHERN SHIFT OF THE 12Z UKMET WHICH WAS SOMEWHAT INFLUENCED BY A SLIGHTLY FASTER/STRONGER UPSTREAM FEATURE. USUALLY THE UKMET IS A SIGN OF A FAVORED TREND SHIFT BUT THE UKMET DOES NOT GO AS AGGRESSIVE/DEEP WITH THE SURFACE LOW AS THE GFS AFTER 01/00Z...SO WILL FAVOR CONSISTENCY AND FAVOR THE 12Z CMC/ECMWF AFTER 29/00Z WHICH HAS THE FAVOR OF ECENS AND SREF ENSEMBLE SOLUTIONS. WESTERN TROF OF LARGE HUDSON BAY UPPER CYCLONE DROPPING A WEAK LOW AND FRONT ACROSS THE NORTHERN TIER AND GREAT LAKES MONDAY AND WEAKENING INTO NEW ENGLAND TUES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z CMC/ECMWF BLEND CONFIDENCE: AVERAGE THE WESTERN ARM OF THE LARGE SCALE ARCTIC MID-LEVEL CYCLONE THAT DOMINATES MUCH OF CANADA WILL START TO DROP SOUTHWARD AND SWING THE MAJORITY OF ENERGY THROUGH SOUTHERN CANADA WHILE SHEARING OUT THE LINGERING TROF ENERGY TOWARD THE WEST CLIPPING THE NORTHERN TIER OF THE U.S MONDAY INTO TUESDAY WITH A WEAK SURFACE WAVE AND ASSOCIATED COLD FRONT. THE 12Z NAM IS A BIT NORTH OF THE BEST CLUSTER WITH THE LEADING WAVE BUT ALSO RETAINS A STRONGER WESTERN/LESS SHEARED OUT TROF ENTERING THE NORTHERN U.S...RESULTING IN A STRONGER AND FURTHER SOUTH SURFACE REFLECTION ALONG THE DRAPED COLD FRONT. THE 12Z GFS CONTINUES A TREND OF BEING MUCH FASTER WITH THE WAVE AXIS MOVING THROUGH CENTRAL INTO EASTERN CANADA LEADING TO MORE PHASING/INTERACTION WITH THE DOWNSTREAM WAVE (SEE ABOVE) OUT OF PHASE WITH THE REMAINING GUIDANCE (NON-NCEP GUIDANCE) IS QUITE WELL ALIGNED IN TIMING/STRENGTH AND POSITION THROUGH THE DEPTH OF THE SYSTEM...PARTICULARLY THE 00Z CMC/ECMWF. THESE MODELS ARE ALSO SUPPORTED BY THE 00Z ECENS MEAN WHICH SHOWED FAIRLY TIGHT CLUSTERING WITHIN IT. AS SUCH WILL FAVOR A NON-NCEP BLEND WEIGHTING TOWARD THE CMC/ECMWF MORE AT AVERAGE CONFIDENCE. 19Z UPDATE: THE 12Z UKMET IS A TRENDED A BIT STRONGER LEADING TO A VERY STRONG SURFACE REFECTION WHICH EVENTUALLY BECOMES FAST ACROSS S QUEBEC AND WITH UPSTREAM ISSUES THE ORIENTATION OF THE FRONT BECOMES A BIT LESS FAVORABLE. THERE WAS A SLIGHT SHIFT FASTER WITH THE 12Z ECMWF/CMC BUT ARE FAIRLY CONSISTENT WITH THE FRONT ORIENTATION. THIS ALSO BRINGS SOME QUESTION OF INCLUSION OF THE 12Z GFS GIVEN ITS BETTER AGREEMENT UPSTREAM TOO...BUT SURFACE REFLECTION IS VERY WEAK/NON-EXISTENT DUE TO THE SPEED OF THE WAVE ALOFT TO SUPPORT IT FULLY BUT MAY HELP CONTRIBUTE TO SOME POSITIVE BLENDING NEARER THE UPSTREAM WAVE OVER THE GREAT LAKES LATE MON INTO TUES. STILL OVERALL BLEND WILL SUPPORT A 12Z CMC/ECMWF BLEND AT AVERAGE CONFIDENCE. SYSTEM MOVING THROUGH THE NORTHWEST SUNDAY/MONDAY AND DIGGING SOUTHEAST INTO THE PLAINS TUESDAY...LEADING TO SURFACE CYCLONE INTO THE CENTRAL US BY TUES EVENING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF CONFIDENCE: SLIGHTLY BELOW AVERAGE THE MODEL TRENDED TOWARD BETTER AGREEMENT WITH A BROADER TROF ENTERING THE PACIFIC NORTHWEST SUNDAY...WITH SOME LARGER VARIATION WITH THE DEPTH NORTH TO SOUTH OF THE TRAILING BACK HALF OF THE WAVE. THE 12Z GFS/NAM BOTH ARE FURTHER NORTH WITH THE TRAILING EDGE. THE 12Z GFS DID ALLOW FOR A BIT MORE OF THE SHEAR AXIS ENERGY TRAVELING THROUGH THE SOUTHERN CANADIAN ROCKIES TO INTERACT WITH THE LEADING EDGE OF THE TROF TO HELP ACCELERATE THE OVERALL TROF SOUTHEAST AND DIG ACROSS THE PLAINS FASTER THAN THE 00Z/06Z RUNS. THIS HELPED TO TREND TOWARD A MORE FAVORABLE CONSISTENT 06Z GEFS AND CLOSER TO THE 00Z ECENS MEAN. THE 00Z ECMWF IS MOST WRAPPED UP ACROSS IA BY DAY 3 LEADING TO A MORE VERTICAL/NEUTRAL TILT TO THE TROF OVERALL WHICH SEEMS A BIT LESS LIKELY GIVEN THE MORE PROGRESSIVE NATURE FROM WEST TO EAST...STILL IT REMAINS FAIRLY CENTRAL TOWARD THE MIDDLE GROUND AND BLENDING WITH THE 12Z GFS MAY BEST REPRESENT THE ENSEMBLE MEANS. UNCHARACTERISTICALLY...THE 00Z CMC IS FASTER AND FURTHER NORTH WHILE THE 00Z UKMET IS SLOWER AND SOUTHWEST OF THE CENTRAL CLUSTER TO NOT INCLUDE IN THE PREFERENCE AT THIS TIME. GIVEN THE LARGE SPREAD BUT GOOD MIDDLE GROUND COMPROMISE WILL FAVOR THE 00Z ECENS MEAN/06Z GEFS MEAN ON DAY 3 AND WILL BLEND THE 12Z GFS/00Z ECMWF TO REPRESENT THEM FAIRLY WELL. CONFIDENCE IS AVERAGE IN THIS BLEND. 19Z UPDATE: DUE TO A SLIGHTLY FASTER NORTHERN STREAM TROF (SEE SECTION ABOVE)...THE LEADING PORTION OF THE WAVE ENTERING THE PACIFIC NORTHWEST WAS PICKED UP LEADING TO A MUCH FASTER AND FLATTER SOLUTION THAN THE 00Z ECMWF ACTUALLY TRENDING FASTER THAN A FASTER/FLATTER 12Z GFS. THIS APPEARS TO HAVE SOLVED SOME OF THE CONCERN WITH THE 00Z ECMWF BUT MAYBE THE SWING WAS TO THE OPPOSITE SIDE OF THE SPECTRUM OF SOLUTIONS. THE 12Z UKMET IS MUCH FASTER IN THE NORTHERN STREAM AND MUCH SLOWER/WRAPPED UP IN THE SOUTHERN STREAM. THE 12Z CMC COULD BE BLENDED IN TO KEEP A BIT OF CONTINUITY BUT IT IS ALSO A BIT TOO FAST WITH THE COLD FRONT PROGRESSION THROUGH THE MS RIVER VALLEY BY THE END OF THE FORECAST PERIOD TO FULL SUPPORT IT. WILL CONTINUE TO SUPPORT A 12Z GFS/ECMWF BLEND BUT THIS MAY CAUSE SOME CHANGES PARTICULARLY ACROSS THE NORTHERN AND SOUTHERN PORTIONS OF THE SYSTEM WHERE SPREAD IS THE LARGEST. CONFIDENCE IS FAIRLY GOOD THROUGH THE MIDDLE BUT SLIGHTLY BELOW AVERAGE ON THE NORTHERN/SOUTHERN PORTIONS. NEXT PACIFIC WAVE ENTERING NORTHWEST U.S. BY TUESDAY EVENING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF/CMC BLEND CONFIDENCE: SLIGHTLY BELOW AVERAGE IN THE WAKE OF THE PRIOR WAVE...INCREASED RIDGING OCCURS ACROSS THE NW PACIFIC REGION WITH STRONG SOUTHWESTERLY FLOW TO IMPACT VANCOUVER ISLAND AND W WA BEFORE THE NEXT WAVE MOVES THROUGH TOWARD THE END OF THE FORECAST PERIOD...PLEASE REFER TO QPFPFD FOR ADDITIONAL QPF DETAILS. AS FOR THE MASS FIELDS...THERE IS QUITE A DIVERSE STYLE OF THE WAVE THOUGH THE TIMING OF THE WAVE IS GENERALLY FAIR IN AGREEMENT. A FULLY WRAPPED UP CLOSE LOW IN THE 12Z NAM COMPARES TO A HIGH-AMPLITUDE/NARROW TROF IN THE GFS WITH VARYING EVOLUTIONARY POINTS IN BETWEEN WITH THE OTHER GUIDANCE. THE 12Z GFS IS SUPPORTED BY THE 00Z ECMWF WHICH IS A NARROW WAVELENGTH BUT AMPLIFIED TROF...BOTH ARE EQUALLY SUPPORTED BY THEIR ENSEMBLE MEANS THOUGH THERE REMAINS A FAIR BIT OF SPREAD WITHIN EACH ENSEMBLE TO AVERAGE OUT THE DEEPER/AMPLIFIED TROF A BIT MORE THAN THE OPERATIONAL RUNS. THE 12Z NAM IS BEST SUPPORTED BY THE 00Z CMC WHICH IS NEARER TO CLOSING OFF A LOW JUST OFF VANCOUVER ISLAND NEAR WED...WITH A DEEP SURFACE REFLECTION NOTED... THE 00Z UKMET IS IN BETWEEN BOTH CAMPS IN EVOLUTION BUT ALSO IS FURTHER WEST OUT OF PHASE AND STICKS OUT SIGNIFICANTLY WITHIN THE 00Z ENSEMBLE SPAGHETTI ANALYSIS. GIVEN BETTER CONFIDENCE IN THE GFS/ECMWF OVERALL DUE TO HISTORY WILL FAVOR THIS SOLUTION OVER THE NAM/CMC...HOWEVER GIVEN THE VARIATION INVOLVED CONFIDENCE IN A 12Z GFS/00Z ECMWF BLEND IS SLIGHTLY BELOW AVERAGE. 19Z UPDATE: THE 12Z ECMWF TRENDED TOWARD A SMALL CLOSING UPPER LOW FEATURE AT THE BASE OF THE TROF CLOSER TO TOWARD THE 00Z CMC WHILE SIMILAR TO THE 12Z GFS AS WELL...THE 12Z CMC SCALED BACK A BIT ON THE LARGER DEVELOPING LOW AND LOOKS SIMILAR TO THE 12Z ECMWF IF A SHADE SLOWER (TYPICAL OF BIAS). THE 12Z UKMET HAS RESOLVED ITS TIMING ISSUES PICKING UP PACE TOWARD THE OTHER SOLUTIONS BUT IS ALSO A LARGER/ELONGATED CYCLONE BUT IS STILL A BIT TOO FAR NORTH/STRONGER THAN MUCH OF THE BETTER CLUSTERED MODELS. AS SUCH WILL CONTINUE TO FAVOR A 12Z GFS/ECMWF BLEND AND INCLUDE THE 12Z CMC AT A LOWER WEIGHTING. CONFIDENCE REMAINS SLIGHTLY BELOW AVERAGE. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA