MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 304 PM EDT MON SEP 21 2015 VALID SEP 21/1200 UTC THRU SEP 25/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH FINAL PREFERENCE AND CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ THERE DID NOT APPEAR TO BE ANY INITIALIZATION ERRORS WITH THE NAM/GFS WHICH IMPACTED THEIR FORECASTS. TROPICAL DEPRESSION 16E AND UPSTREAM MID-LEVEL CUT-OFF ENERGY TRACKING THROUGH BAJA CA INTO THE SOUTHWEST US MON/TUES AND INTO CENTRAL ROCKIES/PLAINS MID WEEK ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF CONSENSUS CONFIDENCE: AVERAGE THE REMNANTS OF TROPICAL DEPRESSION 16E WILL MOVE ACROSS ARIZONA THROUGH MONDAY NIGHT. THE AREA OF VORTICITY WITH THIS FEATURE MAY HAVE SOME INTERACTION WITH AN UPPER LOW CURRENTLY OFF THE CALIFORNIA COAST...WITH BOTH FEATURES MOVING INTO COLORADO ON TUESDAY...AND THEN INTO THE CENTRAL PLAINS WEDNESDAY/THURSDAY. THE TREND AMONG THE GUIDANCE...AND SEEN IN LATEST SATELLITE IMAGERY...IS FOR A SLIGHTLY FURTHER EAST TRACK OF THIS UPPER ENERGY ACROSS ARIZONA. IT WOULD APPEAR THAT THE 0Z CMC AND ECMWF ARE A BIT TOO STRONG/NORTHWEST WITH THIS FEATURE. INSTEAD A TRACK CLOSER TO THE 12Z NAM...12Z GFS AND 0Z UKMET MAY MAY BE A MORE LIKELY SOLUTION. AS THE SYSTEM TRACKS ACROSS THE ROCKIES INTO THE CENTRAL PLAINS...THE 0Z CMC APPEARS TO BE A NORTHWEST OUTLIER...WHICH ALSO SHOWS UP IN ITS DAY 2/3 QPF OUTPUT. AT THIS TIME A SOLUTION THAT FAR NORTHWEST HAS LITTLE SUPPORT FROM THE REMAINDER OF THE GUIDANCE SUITE...AND THUS IS NOT PREFERRED. OTHERWISE THE REMAINDER OF THE GUIDANCE IS IN DECENT AGREEMENT...ALTHOUGH THE MINOR DIFFERENCES THAT DO EXIST IN THE LARGE SCALE DO HAVE A CONSIDERABLE IMPACT ON SENSIBLE WEATHER/PRECIPITATION. GIVEN THE LOW CONFIDENCE ON THESE DETAILS...A GENERAL BLEND OF THE 12Z GFS AND 0Z ECMWF WOULD SEEM TO REPRESENT A MOST LIKELY SCENARIO...AS THEY SEEM TO BE SLOWLY TRENDING TOWARDS EACH OTHER. 19Z UPDATE: THE 12Z ECMWF TRENDED TOWARDS THE GFS SOLUTION ON DAY 1 AS EXPECTED...WEAKER AND FURTHER EAST ACROSS ARIZONA. ACROSS THE PLAINS ON DAY 2/3...THE 12Z ECMWF TRENDED CLOSER TO THE 12Z GFS. SO WHILE DIFFERENCES STILL EXIST...THE PREFERRED SOLUTION REMAINS A GFS/ECMWF CONSENSUS. PLEASE SEE THE LATEST NHC DISCUSSION FOR MORE DETAILS ON TROPICAL DEPRESSION 16E. S/W TRAVERSING SOUTHERN CANADA WITH A DRAPED COLD FRONT ACROSS NORTHERN TIER OF U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF OPERATIONAL MODELS CONFIDENCE: ABOVE AVERAGE IN GENERAL MODELS ARE IN GOOD AGREEMENT WITH THIS FEATURE...WITH NO REASON TO NECESSARILY PREFER ONE SOLUTION OVER ANOTHER. THUS A GENERAL MODEL CONSENSUS SHOULD HANDLE THIS FRONTAL PASSAGE WELL...WITH LIMITED QPF IMPACTS. DEEP LARGE SCALE UPPER LOW IN THE EASTERN GULF OF ALASKA/NORTHERN EAST PACIFIC ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL CONSENSUS CONFIDENCE: AVERAGE A CHANGE OF PATTERN ACROSS THE GULF OF ALASKA WITH STRONG AGREEMENT IN THE DETERMINISTIC AND ENSEMBLE SUITE MAINLY IN THE SCALE/BREADTH OF THE DEEP GLOBAL-SCALE TROF...HOWEVER SMALLER THOUGH IMPORTANT DIFFERENCES EXIST WITH THE EMBEDDED SHORTWAVES LEADING TO DIFFERENCES IN THE POSITIONING OF THE SYNOPTIC SURFACE LOW/FRONTS AND SENSIBLE WX. FAIRLY GOOD AGREEMENT EXISTS WITH THE INITIAL SHARP S/W TO AFFECT BC ON TUESDAY...AFTER THAT TIMING AND STRENGTH DIFFERENCES INCREASE WITH THE SUBTLE SECOND WAVE AND THE STRONGEST/MAIN VORT WAVE THAT EITHER DEEPENS THE CENTER OF THE LOW OR STRINGS OUT THE ENERGY. THE 12Z GFS REMAINS A STRONG/DEEP OUTLIER WITH THE MAIN WAVE WITHIN THE TROUGH...AS WELL AS BEING ON THE QUICKER SIDE OF GUIDANCE. THE ECMWF ON THE OTHER HAND IS ON THE SLOWER END OF THE MODEL SPECTRUM. OVERALL IT IS A COMPLEX SCENARIO GIVEN THE MULTIPLE PIECES OF ENERGY WITHIN THE BROAD TROUGH...AND THUS CONFIDENCE ON THE EVENTUAL EVOLUTION REMAINS LOW. GIVEN THE CONSISTENCY OF THE ECMWF AND GFS FOR THEIR INDIVIDUAL SOLUTIONS...BELIEVE A MOST LIKELY SCENARIO IS REPRESENTED BY A CONSENSUS OF THE TWO AT THIS TIME. THE NAM/CMC/UKMET CAN ALSO BE CONSIDERED WITHIN ANY MULTI MODEL BLEND...AS NONE OF THEM APPEAR TO OFFER AN OUTLYING UNLIKELY SOLUTION...WITH THE NAM/UKMET CLOSER TO THE GFS...AND CMC MORE SIMILAR TO AN ECMWF TYPE SOLUTION. THE GEFS AND ECMWF ENSEMBLE MEANS ALSO SHOW HINTS THAT THE CONSENSUS MIDDLE GROUND SOLUTION IS MOST PROBABLE. 19Z UPDATE: THE 12Z ECMWF TRENDED QUICKER AND CLOSER TO THE GFS WITH THE TIMING OF SHORTWAVE ENERGY IMPACTING THE PACIFIC NORTHWEST. THE ECMWF REMAINS WEAKER THAN THE GFS THOUGH...AND THE PREFERRED SOLUTION REMAINS A GENERAL MODEL CONSENSUS. TROUGH OVER THE APPALACHIANS TUE AND EAST COAST WED --- RETROGRADING A SURFACE LOW FROM THE WESTERN ATLANTIC SHEAR AXIS WEST TOWARD THE CAROLINAS BY WED. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF DETERMINISTIC MODEL CONSENSUS AND SREF/GEFS/ECMWF ENSEMBLE MEANS CONFIDENCE: BELOW AVERAGE MODELS HAVE SHOWN LITTLE RUN TO RUN CONSISTENCY WITH REGARDS TO A POTENTIAL VORT MAX/LOW DEVELOPMENT OFF THE SOUTHEAST COAST WEDNESDAY INTO THURSDAY. THE 0Z CMC IS A STRONG OUTLIER WITH THIS SYSTEM...RESULTING IN MUCH HIGHER QPF ACROSS THE COASTAL CAROLINAS AND GEORGIA. GIVEN THIS IS A BIAS SHOWN BY THIS MODEL QUITE OFTEN...WILL NOT PREFER A SOLUTION AS DEEP AS IT SUGGESTS AT THIS TIME. HOWEVER THE RECENT TRENDS FROM THE GFS/ECMWF/UKMET ARE ALL CLOSER TO THE COAST...BRINGING AT LEAST SOME PRECIPITATION INTO THE ABOVE MENTIONED AREAS...JUST TO A LESSER DEGREE THAN THE CMC. THE 12Z NAM IS THE ONLY GUIDANCE THAT IS WEAKER/EAST WITH THIS SYSTEM KEEPING A MAJORITY OF THE SENSIBLE WEATHER IMPACTS OFF THE COAST. GIVEN THE LACK OF RUN TO RUN CONSISTENCY...HARD TO COMPLETELY JUMP ONTO THE FURTHER WEST GFS/ECMWF AT THIS TIME. ALTHOUGH GIVEN RECENT TRENDS WILL LEAN IN THAT DIRECTION...MAKING THE NAM A LESS LIKELY SOLUTION. THUS FOR NOW WILL PREFER A SOLUTION IN BETWEEN THE 12Z GFS/0Z ECMWF...AND THE SREF/GEFS/ECMWF ENSEMBLE MEANS (WHICH REPRESENT A WEAKER ALTERNATIVE TO THE DETERMINISTIC RUNS). 19Z UPDATE: THE 12Z ECMWF REMAINED PRETTY CONSISTENT WITH THE 0Z RUN. HOWEVER FOR THE REASONS MENTIONED ABOVE...WILL CONTINUE TO PREFER A SOLUTION BETWEEN THE DETERMINISTIC CONSENSUS AND ENSEMBLE MEANS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... CHENARD