MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 247 PM EDT THU SEP 22 2016 VALID SEP 22/1200 UTC THRU SEP 26/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z GUIDANCE EVALUATION INCLUDING MODEL PREFERENCE AND FORECAST CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ FRONTAL ZONE ACROSS UPPER MIDWEST SHIFTING TOWARD NEW ENGLAND WITH SFC WAVE DEVELOPING BY FRIDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE SHORTWAVE ENERGY FROM DYING MCS ACROSS MIDWEST WILL CONTINUE TO SHEAR/ELONGATE INTO DEEPENING GLOBAL TROF/HUDSON LOW OVER THE NEXT DAY OR SO ACROSS THE GREAT LAKES; WHILE THE SURFACE BOUNDARY REMAINS FAIRLY STATIONARY AND A FOCUS OF POOLED MST/RAINFALL POTENTIAL INTO NEW ENGLAND. A STRONG SHORTWAVE ON THE SW PERIPHERY OF THE HUDSON LOW LEADS TO HEIGHT FALLS ACROSS SE CANADA INTO NEW ENGLAND BY FRIDAY SUPPORTING A WEAK SURFACE WAVE ALONG THE FRONT TO AMPLIFY AND SHIFT FROM MAINE TO SW NEWFOUNDLAND BY SAT. MODEL CONSENSUS IS FAIRLY TIGHT GIVEN THE CONFLUENCE OF THE STREAMS WITH NO MAJOR SHIFTS SEEN IN THE 12Z NAM/GFS...AS SUCH WILL CONTINUE TO FAVOR A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE FOR THESE SYSTEMS. 19Z UPDATE: NO SIGNIFICANT CHANGE WERE DENOTED TO REMOVE ANY GUIDANCE FROM A GENERAL MODEL BLEND. LINGERING MID-LEVEL LOW/JULIA'S REMAINS ACROSS COASTAL SOUTHEAST ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE MODELS REMAIN IN FAIRLY GOOD AGREEMENT THROUGH MUCH OF THE SHORT TERM AS THE REMAINING MID-LEVEL ENERGY OF JULIA/NORTHERN STREAM SHORTWAVE COMBINATION CONTINUES TO FILL. THERE IS FAIRLY GOOD AGREEMENT AS WELL AS THE NORTHERN STREAM TROF ACROSS NEW ENGLAND SHEARS THE NORTHERN ENERGY OF THE TROF OUT INTO THE ATLANTIC FRIDAY; RESULTING IN A RE-CONSOLIDATION OF THE REMAINING ENERGY SOUTH ACROSS GA WHERE IT SHOWS SOME HINT OF RETROGRESSION TO THE WEST. THE SPREAD DIFFERENCES ARE MINOR THOUGH THE 00Z ECMWF REMAINS THE MOST COMPACT/STRONGEST WITH THE UKMET AND 12Z GFS SUPPORTING IT WHILE THE 12Z NAM/00Z CMC ARE MOST WASHED OUT. IN GENERAL THESE DIFFERENCES ARE TOO SMALL FOR SIGNIFICANT IMPACT DIFFERENCES AND AS SUCH SUPPORT IS FOR A GENERAL MODEL BLEND AT SLIGHTLY ABOVE AVERAGE CONFIDENCE FOR THIS ENERGY. 19Z UPDATE: THOUGH THERE WAS LITTLE DIFFERENCE BEFORE...THE SMALL ADJUSTMENTS WITH THE 12Z NON-NCEP MODELS FURTHER SOLIDIFIED THE CLUSTER OVERALL. DEEP CYCLONE SWINGING THROUGH THE WEST INTO THE NORTHERN PLAINS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF/UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE CYCLONE REMAINS ABOUT 3 STD DEV BELOW NORMAL AS IT TRAVERSES THE GREAT BASIN INTO THE CENTRAL ROCKIES BUT MODELS AND ENSEMBLES SHOW FAIRLY SOLID AGREEMENT THROUGH THIS TIME PERIOD. SMALL DIFFERENCES IN TIMING OF INTERNAL SHORTWAVES BEGIN TO LEAD TO LARGER DIFFERENCES OVERALL SATURDAY INTO SUNDAY AS THE MAIN UPPER LOW LIFTS NORTHEAST INTO WY SUPPORTING STRONG LEE CYCLONE FROM NE CO TRACKING TO MT/ND. AT THE SAME TIME...ADDITIONAL UPSTREAM ENERGY WILL ALSO DIG THE TROF INTO NEW MEXICO BUT WILL FOCUS A FULL SECTION BELOW TO ADDRESS THIS ENERGY. BY LATE SAT...THE 12Z NAM BREAKS FROM SOLID CONSENSUS SHIFTING FASTER AND FURTHER EAST...LEADING TO A SURFACE LOW WELL EAST OF BETTER CONSENSUS. THE 06Z GEFS AND 00Z ECENS MEANS REMAIN WELL AGREED UPON AND THOUGH THERE ARE MINOR DIFFERENCES IN CENTER POSITIONS THE 00Z ECWMF AND 12Z GFS REPRESENT THEM WELL. THE 12Z GFS SHOWED LITTLE CHANGE FROM THE 00Z/06Z RUNS...IT DOES REMAIN FASTER AND SLIGHTLY EAST WHILE THE 00Z ECMWF IS A BIT MORE WEST AND WRAPPED UP BOTH IN LINE WITH THEIR TYPICAL BIAS...BUT SOMETHING THAT IS COMFORTABLE IN BUILDING CONSISTENCY AND CONFIDENCE OVERALL. THE 00Z UKMET FAVORS A SOLUTION CLOSER TO THE GFS...PROVIDING AN EVER SO SLIGHT FAVORITISM TO THOSE SOLUTIONS AS WELL. THE 00Z CMC FOLLOWS ITS TREND OF DEEPER SOLUTIONS...NEARING THE ECMWF BUT ALSO REMAINS JUST OUT OF PHASE ENOUGH (MAINLY IN THE LOWER LEVELS) TO KEEP OUT OF THE PREFERENCE AT THIS TIME. AS SUCH A 12Z GFS AND 00Z ECMWF/UKMET BLEND IS PREFERRED AT SLIGHTLY ABOVE AVERAGE CONFIDENCE. 19Z UPDATE: MODELS CONTINUE IN GOOD AGREEMENT THROUGH 00Z SAT AND MODERATELY SO THEREAFTER WITH SOME ADJUSTMENTS SEEN IN THE 12Z UKMET/ECMWF BOTH PIVOTING A BIT SLOWER ACROSS MT/ND SAT NIGHT/SUN MORNING BEFORE SHIFTING MORE EASTWARD NEARER TO THE 12Z NAM SOLUTION...NOW ABOUT HALF WAY BETWEEN THE NAM AND GFS. THE 12Z CMC REMAINS THE WEAKEST WITH THE INNER CORE OF THE UPPER LOW BUT ALSO IS BROADER/DEEPER WITH THE OVERALL TROF AS A WHOLE...AS SUCH REMAINS AN OUTLIER BY FAVORING A NARROWER MORE NEUTRAL TILT OF THE TROF THROUGHOUT THE ENTIRE U.S. PLAINS. OVERALL THE SPREAD MUDDLES THE CONFIDENCE ON DAY 3 A BIT...BUT WILL CONTINUE TO SUPPORT THOSE MODELS NEAR THE GEFS/ECENS MEAN WHICH INCLUDE THE 12Z GFS/UKMET/ECMWF. SYSTEM CLOSING OFF IN NM EARLY SUNDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND CONFIDENCE: AVERAGE AS STATED ABOVE...UPSTREAM SHORTWAVE ENERGY REACHES THE MAIN TROF AXIS ON SATURDAY AND BEGINS TO DESCEND IN LATITUDE EVENTUALLY STARTING TO CLOSE OFF A SEPARATE UPPER LOW CENTER ACROSS NEW MEXICO BY SUNDAY MORNING. MODEL DIFFERENCES THOUGH GENERALLY SMALL APPEAR TO BE RELATED TO SPACING/TIMING DIFFERENCES OF THE SHORTWAVE EXITING OUT OF THE CENTRAL PLAINS. AS SUCH A SLOW ECMWF SOLUTION ALLOW THIS THIS WAVE TO DESCEND SOUTH FURTHER/FASTER WITH MORE VIGOR THAN THE FASTER GFS...RESULTING IN A DEEPER MORE CONSOLIDATED CLOSED LOW FEATURE COMPARED TO THE ELONGATED (SW-NE) TROF AXIS FURTHER EAST OF THE GFS. BY SUNDAY EVENING SOME RETROGRADING WEST IS SHOWN BUT A VAST MAJORITY OF GUIDANCE/ENSEMBLE MEMBERS IRRESPECTIVE OF STRENGTH. THE 00Z CMC IS MOST OUT OF PHASE BY THE END OF THE FORECAST PERIOD WITH A DEEPER/BROADER TROF THAT REMAINS GENERALLY CONNECTED TO THE NORTHERN LOW...IE VERY SLOW EVOLUTION COMPARED TO THE REST OF THE GUIDANCE. THE 00Z ECMWF IS CLUSTERED WELL WITH THE 00Z UKMET WHILE THE 12Z NCEP SOLUTIONS ARE A BIT FURTHER EAST (GFS MUCH LESS CONSOLIDATED) THE OVERALL PATTERN MATCH IS WELL ENOUGH GIVEN THE ENSEMBLE SPREAD TO SUPPORT A NON-CMC BLEND AT AVERAGE CONFIDENCE...WEIGHTING CLOSER TOWARD THE ECMWF/UKMET SOLUTIONS. 19Z UPDATE: THE ECMWF APPEARS TO HAVE SHED MORE ENERGY INTO THE NORTHERN STREAM WITH THE 12Z RUN LEADING TO A BROADER AND SHALLOWER LOW ACROSS NM/SE AZ BY 00Z MONDAY MATCHED BY THE 12Z UKMET. THE 12Z CMC REMAINS VERY SLOW TO EVOLVE AND EVEN BY DAY 3 REMAINS ALIGNED/CONNECTED WITH THE NORTHERN STREAM ENERGY MAKING IT A CLEAR OUTLIER FROM AN OTHERWISE SOLID AGREEMENT. AS SUCH WILL CONTINUE A NON-CMC BLEND AT AVERAGE CONFIDENCE. SHORTWAVE AND FRONTAL ZONE APPROACHING PACIFIC NORTHWEST AND WESTERN CANADA BY FRIDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE MODELS AND ENSEMBLES SHOW STRONG CLUSTERING WITH RESPECT TO THE FRONTAL ZONE DESCENDING THROUGH BRITISH COLUMBIA THURSDAY INTO FRIDAY WITH IMPACTS TO THE NORTHWEST COAST AFTER 12Z ON FRIDAY. THERE ARE MINOR DIFFERENCES WITH SOME ISOLATED SPOT SURFACE WAVES ALONG THE FRONT...BUT OVERALL THE TIMING/ORIENTATION AND STRENGTH SEEM WELL ENOUGH AGREED UPON TO SUPPORT A GENERAL MODEL BLEND AT ABOVE AVERAGE CONFIDENCE FOR THIS SYSTEM. 19Z UPDATE: NO SIGNIFICANT CHANGE WERE DENOTED TO REMOVE ANY GUIDANCE FROM A GENERAL MODEL BLEND. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA