MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 251 PM EDT WED AUG 05 2015 VALID AUG 05/1200 UTC THRU AUG 09/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION WITH FINAL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT APPEAR TO DEGRADE THEIR SHORT RANGE FORECASTS. CLOSED LOW MOVING INTO THE WEST FRIDAY DEEP CYCLONE APPROACHING HAIDA GWAII LATE FRIDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE REMAINS IN GOOD AGREEMENT WITH THESE SYSTEMS. POSSIBLE CLOSED LOW NEAR THE CENTRAL US/CAN BORDER FRI PRECEDING SHORTWAVE MOVING INTO LAKE SUPERIOR FRI NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON NAM CONSENSUS CONFIDENCE: AVERAGE THE 12Z NAM/GFS ARE TRENDING STRONGER/SOUTH WITH THE LEAD SHORTWAVE THURSDAY INTO FRIDAY ACROSS THE DAKOTAS INTO MN/IA. THE 12Z NAM IS ON THE DEEPER EDGE OF GUIDANCE AND APPEARS TOO STRONG/SOUTH WITH THIS WAVE. THE REST OF THE GUIDANCE APPEARS TO BE CLOSE ENOUGH TO CONSIDERED A POSSIBLE SOLUTION. THERE IS GENERALLY GOOD AGREEMENT WITH THE CLOSED LOW MOVING ACROSS SOUTHERN CANADA THURSDAY INTO SATURDAY. THE GENERAL TREND OVER THE PAST FEW MODELS CYCLES HAS BEEN FOR A FURTHER NORTH TRACK WITH THIS SYSTEM BY LATER FRIDAY INTO SATURDAY. THE 0Z ECMWF APPEARS A BIT QUICK WITH THIS FEATURE BEING FASTER THAN THE OTHER DETERMINISTIC GUIDANCE AND ITS ENSEMBLE MEAN...BUT OVERALL THE DIFFERENCES ARE PRETTY MINOR. FINAL PREFERENCE UPDATE: WITH THE LEAD SHORTWAVE THE 12Z ECMWF HAS INDEED TRENDED A BIT TOWARDS THE STRONGER/SOUTH SIDE TO COME MORE IN LINE WITH THE 12Z GFS. THE 12Z UKMET/CMC ALSO SEEM TO OFFER REASONABLE SOLUTIONS AND REMAIN CLOSE TO THE ECMWF/GFS...THUS NO CHANGE IN THE PREFERENCES AT THIS TIME. WITH THE CLOSED LOW...THE 12Z ECMWF/CMC/UKMET GUIDANCE REMAINS IN PRETTY GOOD AGREEMENT. THE ECMWF HAS TRENDED A BIT SLOWER...BUT STILL REMAINS ON THE QUICKER SIDE OF THE GUIDANCE DISTRIBUTION. EASTERN TROUGH SURFACE LOW NEAR THE EAST COAST SATURDAY MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF BLEND CONFIDENCE: AVERAGE INITIALLY A MAJORITY OF THE GUIDANCE ARE IN GOOD AGREEMENT WITH THE TROUGH MOVING INTO THE EAST COAST THURSDAY INTO FRIDAY. IN GENERAL THE TREND HAS BEEN FOR A MORE SOUTHERN SHORTWAVE TRACK. THUS ONLY THE 0Z UKMET REALLY APPEARS TO BE AN OUTLIER AT THIS POINT...BEING TOO STRONG AND NORTH. BY LATER FRIDAY INTO SATURDAY MODEL DIFFERENCES BEGIN TO INCREASE. THESE DIFFERENCES ARE DUE TO TWO FACTORS...FIRST THE STRENGTH OF THE INITIAL WAVE/LOW MOVING OFF THE CAROLINA EAST COAST FRIDAY EVENING...AND SECOND THE AMOUNT OF SHORTWAVE ENERGY DIVING SOUTHEAST OUT OF THE GREAT LAKES AND POTENTIALLY REINFORCING THE TROUGH. THE GENERAL TREND OVER RECENT MODEL CYCLES HAS BEEN FOR A WEAKER WAVE/LOW OFF THE COAST AND FOR MORE ENERGY REINFORCING THE TROUGH BY FRIDAY NIGHT/SATURDAY. THE 0Z UKMET REMAINS AN OUTLIER WITH TOO STRONG OF A LOW...AND THE 0Z CMC APPEARS TOO WEAK WITH THE ADDITIONAL SHORTWAVE ENERGY DIVING SOUTHEAST. THUS NEITHER OF THESE ARE PREFERRED AT THIS TIME. THE 12Z GFS/NAM ARE THE WEAKEST WITH THE INITIAL WAVE AND STRONGEST/DEEPEST WITH THE ADDITIONAL ENERGY DIGGING INTO THE TROUGH BY SATURDAY. GIVEN THIS MATCHES RECENT TRENDS AMONG ALL THE GUIDANCE...THEY MAY HAVE THE MOST ACCURATE DEPICTION. HOWEVER..CAN NOT COMPLETELY RULE OUT A SOLUTION CLOSER TO THE 0Z ECMWF. THUS THE WPC PREFERENCE IS FOR A 12Z NAM/GFS AND 0Z ECMWF CONSENSUS...HEDGED TOWARDS THE GFS/NAM. FINAL PREFERENCE UPDATE: THE 12Z UKMET REMAINS A STRONG/NORTH/FAST OUTLIER AND THE 12Z CMC STILL SEEMS TOO WEAK IN GENERAL WITH THE SHORTWAVE ENERGY. THE 12Z ECMWF HAS INDEED TRENDED CLOSER TO THE 12Z GFS/NAM WITH THE EAST COAST TROUGH LATER FRIDAY INTO SATURDAY. HOWEVER IT REMAINS STRONGER WITH THE INITIAL SHORTWAVE AND SURFACE LOW OFF THE EAST COAST. SO CONFIDENCE IN THE TROUGH LOCATION/DEPTH/TIMING IS INCREASING...BUT STILL LOWER CONFIDENCE ON THE EXACT STRENGTH OF THE WAVE AND LOW. A CLOSER LOOK SUGGESTS THE 12Z NAM HANDLING OF THE SHORTWAVE ENERGY AND RESULTANT LOW OFF THE COAST SEEMS A BIT OFF. THUS THE ONLY CHANGE TO THE WPC PREFERENCE IS TO REMOVE THE NAM...AND GO WITH A 12Z ECMWF/GFS CONSENSUS. THIS CONSENSUS MATCHES THE 12 GEFS MEAN QUITE WELL WITH REGARDS TO THE TIMING/LOCATION OF THE SURFACE LOW MOVING UP THE COAST. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... CHENARD