MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 303 AM EDT MON SEP 21 2015 VALID SEP 21/0000 UTC THRU SEP 24/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS MODEL EVALUATION WITH FORECAST 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 MID WEEK ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z ECMWF/CMC CONFIDENCE: PLEASE SEE NHC DISCUSSION FOR ADDITIONAL DETAILS PER NHC FORECAST OF 16E THERE IS STRONG MODEL AGREEMENT IN THE TRACK WITH HEAVIER WEIGHTING TOWARD THE 12Z ECMWF....WHICH HAS CONTINUED THROUGH THE 00Z ECMWF. THOUGH DIFFERENCES OCCUR AFTER THE LOW HAS DISSIPATED ON TUESDAY BEING A BIT FARTHER EAST THAN ITS 12Z RUN CONTINUING A TREND TYPICALLY FOLLOWED BY THE ECENS MEAN OVER THE LAST DAY OR SO. THOUGH THE 00Z ECMWF DOES RETAIN SOME ENERGY OF THE UPSTREAM CUT-OFF AND STRINGS IT ALONG EVENTUALLY ABSORBING IT BY 23/12Z WED AS THE WAVE EJECTS OUT OF THE CENTRAL ROCKIES. THE 00Z CMC HAS BECOME IN MUCH STRONGER AGREEMENT SHIFTING A BIT WEST AND STRONGER MOVING DUE NORTH THROUGH AZ...BEFORE SHIFTING EAST ON A SIMILAR TRACK AS THE 00Z ECMWF...INCLUDING THE HANDLING OF THE SHEARING OUT UPSTREAM CUT-OFF ENERGY. THE 00Z UKMET STILL REMAINS THE EASTERN SIDE OF THE ENVELOPE THOUGH IN A SIMILAR MANNER SHEARS OUT THE UPSTREAM CUT-OFF. THE 00Z GFS A LARGE SHIFT EAST NEARLY ELIMINATING INTERACTION WITH THE CUT-OFF WITH A GENERAL VERY WEAK SOLUTION COMPARED TO THE REST OF THE SUITE AS BOTH SHEAR OUT INTO A BROADER SOUTHWESTERLY FLOW...WHICH IS NOT AS WELL SUPPORTED. THE 00Z NAM QUICKLY IS MUCH TOO STRONG WITH THE SURFACE FEATURE BUT QUICKLY SHEARS IT INTO THE DEFORMATION ZONE/TROF AXIS OVER THE FOUR-CORNERS REGION...AND RETAINING THE BULK/STRENGTH OF THE ENERGY WITH THE UPPER LOW MAKING IT A BIT STRONG COMPARED TO THE NHC PREFERENCE OF THE 00Z ECMWF/CMC. FOR MORE QPF DETAILS PLEASE SEE WPC QPFPFD...FOR MORE TRACK DETAILS PLEASE SEE WTPZ41 KNHC. S/W CURRENTLY OVER BC TRAVERSING SOUTHERN CANADA WITH A DRAPED COLD FRONT ACROSS NORTHERN TIER OF U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF 00Z OPERATIONAL MODELS CONFIDENCE: ABOVE AVERAGE STRONG DETERMINISTIC AND ENSEMBLE MEAN CLUSTERING WITH THE ELONGATED SHORTWAVE ACROSS BC AND DEVELOPING SURFACE LOW IN SOUTHERN ALBERTA. WITH CONTINUED STRONG CLUSTERING RELATING TO THE DEPTH/SPEED/LOCATION OF THE LOW AS IT TRANSVERSES SOUTHERN CANADA. THE 18Z GEFS IS FORWARD/FASTER EVER SO SLIGHTLY ALONG WITH THE 00Z GFS...WITH THE TIMING OF THE FRONT BY A FEW HOURS AS IT CROSSES NORTHERN MN/LK SUPERIOR TUESDAY MORNING...OTHERWISE STRONG ENOUGH CLUSTERING SUPPORTS A BLEND OF THE 00Z OPERATIONAL MODELS AT ABOVE AVERAGE CONFIDENCE. SOME DIFFERENCES DO ARRIVE ACROSS THE CENTRAL GREAT PLAINS ON WED MAINLY DRIVEN BY DIFFERENCES WITH THE EJECTING ENERGY OF THE REMNANTS OF TD 16E. A PREFERENCE THERE TO NON-NAM/SREF SOLUTIONS AS THEY APPEAR TOO STRONG/FAST MAKING THEM LIKELY TO ABSORB INTO THE NORTHERN STREAM RATHER THAN STALLING AND DROPPING SOUTH LIKE MUCH OF THE OTHER DETERMINISTIC AND ENSEMBLE SUITE SUGGESTIONS. DEEP LARGE SCALE UPPER LOW IN THE EASTERN GULF OF ALASKA/NORTHERN EAST PACIFIC ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-CMC BLEND 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 AMPLIFYING/NARROWING THE WAVELENGTH OF THE LARGE SCALE TROF ON THURSDAY. THE NCEP SUITE (00Z NAM/00Z GFS) IS VERY STRONG WITH THE THIRD/MAIN WAVE..FASTER AND MORE CONSOLIDATED DEVELOPING A LOW 990S SURFACE LOW AND DRAWING TROPICAL MOISTURE FASTER/NEARER THE U.S. BY THE END OF THE PERIOD...BUT EFFECTIVELY BY-PASSING THE HEAVIEST PRECIPITATION INTO CANADA BY DAY 4. THE 00Z UKMET REMAINS IN LINE WITH TIMING TO THE 00Z NAM/GFS...HOWEVER ALSO REMAINS A BIT LESS CONSOLIDATED EFFECTIVELY NARROWING THE WAVELENGTH MAKES IT A BIT WEAKER. THE 00Z CMC APPEARS TO HAVE A SHEARED THE SECOND AND THIRD WAVES INTO FOUR SMALLER WEAKER PIECES...THIS SLOWS THE ADVANCEMENT OF THE FRONT AND DEVELOPMENT OF THE SURFACE LOW FURTHER EAST AND WEAKER BY 24/12Z WITH LESS SUPPORT OF ENSEMBLES OR ITS PRIOR 12Z RUN. THE 00Z ECMWF HAS SIMILAR TIMING OF THE WAVES TO THE 00Z GFS/NAM BUT NOT AS STRONG WITH THE CENTRAL LOW... THOUGH THE ORIENTATION OF THE MAIN TROF IS NOT TOO BAD...THE WEAKER SURFACE REFLECTION ALLOWS FOR A FORWARD OCCLUDED/COLD FRONT NEARER THE COAST...BUT WITH SIMILAR TRACKING OF THE MOISTURE/AR INTO VANCOUVER ISLAND THROUGH THE END OF THE FORECAST PERIOD. WPC MEDIUM RANGE HAS BEEN FAVORING AN HIGHER WEIGHTED ECENS MEAN PREFERENCE. GIVEN OVERALL LARGE SCALE AGREEMENT DO NOT SEE MUCH REASONING TO LOCK INTO THIS STRONGER NCEP SOLUTION ON THE SMALLER SCALE....BUT BLEND IT WITH WELL ORIENTED FEATURES WITHIN THE 00Z UKMET/ECMWF AND 18Z GEFS AS SUCH THE PREFERRED BLEND IS NON-CMC BLEND THOUGH HEAVILY WEIGHTED TOWARD THE ENSEMBLE MEANS (18Z GEFS/12Z ECENS MEAN) AT AVERAGE CONFIDENCE. CLOSED 700 MB LOW IN THE OHIO VALLEY SUNDAY NIGHT THROUGH MON AND 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 00Z GFS/UKMET/ECMWF CONFIDENCE: AVERAGE DETERMINISTIC AND ENSEMBLE SUITE HAVE GENERAL AGREEMENT ON EVOLUTION OF THE CLOSED 7H LOW ALONG OH/KY BOARDER WITH 5H LOW OVER NIAGARA REGION...HOWEVER DIFFERENCES BEGIN TO INCREASE WITH THE DEVOLUTION INTO A BROAD SHEAR AXIS FROM WESTERN NEW ENGLAND THROUGH THE EASTERN GULF. THE 00Z NAM SPLITS ENERGY TOWARD THE BASE OF THE TROF AS WELL AS QUICKLY SHEARING EAST ACROSS NEW ENGLAND INTO THE MID-ATLANTIC LEAVING A WEAK VOID ACROSS THE CAROLINAS. ON THE OTHER SIDE OF THE SPECTRUM...THE 00Z GFS WITH SUPPORT OF ITS GEFS ENSEMBLE SUITE AS A WIDER MORE CONSOLIDATED VORT ELONGATED ACROSS THE NORTHERN CAROLINAS AND MID-ATLANTIC MAKING IT LESS SUSCEPTIBLE TO SHEARING FORCES IN EFFECT REMAINING RELATIVELY STATIONARY/RETROGRADING SLIGHTLY BY THE END OF THE PERIOD. THE 00Z CMC/UKMET REMAIN CLOSE IN SPIRIT TO THE GFS...THOUGH THE UKMET SHEARS MORE ENERGY INTO THE NORTHERN STREAM AND KEEPS IT FURTHER EAST WHILE THE 00Z CMC RETAINS MOST OF THE ENERGY SOUTH TOWARD THE CAROLINAS. THE 00Z ECMWF CONTINUES TO RESOLVE A STRONGER VORT AT THE BASE OF THE TROF OVER THE EASTERN GULF SIMILAR TO THE 00Z NAM BUT HAS SHIFTED TO A SIMILAR SHEARING PATTERN TO THE 00Z GFS/UKMET/CMC BUILDING CONFIDENCE IN THIS EVOLUTION. HOWEVER... THE CMC SHOWS SOME KNOWN BIAS ISSUES ACROSS THE SOUTHEAST OVER DEVELOPING A SURFACE CYCLONE AND VORT MAX INTO THE CAROLINAS BY THE END OF THE PERIOD...MAKING IT LESS RELIABLE TO ADD TO THE BLEND FULLY. AS SUCH THE PREFERRED BLEND IS 00Z GFS/UKMET/ECMWF AT AVERAGE CONFIDENCE GIVEN REMAINING VARIABILITY IN SUCH WEAK FEATURES. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... GALLINA