MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 101 PM EDT TUE MAR 17 2015 VALID MAR 17/1200 UTC THRU MAR 21/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT RANGE FORECASTS. UPPER TROUGH APPROACHING THE WEST COAST ON FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 06Z GEFS / 00Z ECMWF MEAN CONFIDENCE: BELOW AVERAGE IMPACTS TO THE PACIFIC NORTHWEST FROM THIS FEATURE ARE STRONGLY TIED TO A SHORTWAVE MOVING THROUGH THE BASE OF AN UPPER TROUGH NEARING THE WEST COAST LATE IN THE DAY ON FRI. THERE IS POOR AGREEMENT IN THE DETERMINISTIC GUIDANCE AND THERE IS PLENTY OF ROOM FOR ADJUSTMENTS IN FUTURE MODEL RUNS. THEREFORE...A PREFERENCE FOR THE SMOOTHED OUT ENSEMBLE MEANS IS PREFERRED GIVEN THEIR GOOD AGREEMENT IN THE MIDDLE. UPPER TROUGH SLOWLY PROGRESSING EWD NEAR THE WRN U.S./MX BORDER THROUGH FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON 00Z CMC COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 00Z CANADIAN APPEARS TO BE AN OUTLIER WITH THE CLOSED LOW TOWARD THE END OF THE SHORT RANGE PERIOD...WITH A SOMEWHAT QUICKER TRACK ACROSS CONUS/MEXICO BORDER. A NON 00Z CMC COMPROMISE REPRESENTS A GOOD CONSENSUS AT THIS POINT IN TIME. CLOSED LOW OVER MEXICO WEAKENING OVER THE DEEP SOUTH THROUGH THU ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS / 00Z ECMWF BLEND CONFIDENCE: AVERAGE THE 12Z NAM/GFS ARE SLIGHTLY FASTER TO BRING THE 850-500 MB LOW INTO THE SRN PLAINS TONIGHT COMPARED TO THE 00Z ECMWF/UKMET/CMC. THE NAM/GFS ARE ALSO MORE DEFINED WITH THE SHORTWAVE AS IT REACHES THE SOUTHEAST THU MORNING. THE INDIVIDUAL MODELS HAVE BEEN CONSISTENT WITH THEIR PRIOR RUNS SO TRENDS DO NOT HELP IN THIS CASE. THE LATEST ENSEMBLE MEANS SUPPORT A TIMING/DEPTH BETWEEN THE FASTER/SLOWER SOLUTIONS...SO A BLEND OF THE FASTER GFS AND SLOWER ECMWF WILL BE PREFERRED. PACIFIC NORTHWEST SHORTWAVE TREKKING INTO THE MIDWEST BY FRI SURFACE LOW NEAR THE MID-ATLANTIC COAST FRI NIGHT ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z UKMET / 12Z NAM BLEND CONFIDENCE: BELOW AVERAGE THE 00Z CMC BECOMES SLOWER THAN THE REMAINING MODEL CONSENSUS BY THU EVENING WITH A SHORTWAVE PASSING OVER THE NRN PLAINS...AND BY THE TIME THIS UPPER FEATURE NEARS THE EAST COAST LATE FRI...THE 00Z ECMWF IF ONE OF THE FASTER MODELS. NO SIGNIFICANT TIMING TRENDS WERE NOTED WITH THIS FEATURE. CURRENTLY...THE 00Z ECWMF ENSEMBLE MEMBERS ARE NORTH OF THE 00Z GEFS...WHICH CORRESPONDS SIMILARLY WITH THE 00Z ECMWF BEING NORTH OF THE 12Z GFS REGARDING A MID-ATLANTIC COASTAL LOW TO DEVELOP ON FRI. THERE IS A RATHER LARGE SPREAD IN THE ENSEMBLE MEMBERS WHICH REDUCES CONFIDENCE IN ANY ONE SOLUTION. HOWEVER...THE 00Z UKMET APPEARS REASONABLE WITH THE TIMING OF THE SHORTWAVE AND SPLITS THE DIFFERENCE WITH THE POSITION OF THE MID-ATLANTIC COASTAL LOW...AND IS MATCHED BY THE 12Z NAM. CLOSED LOW DROPPING SOUTH FROM HUDSON BAY TOWARD END OF WEEK COLD FRONT REACHING THE UPPER GREAT LAKES ON FRI ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 00Z UKMET/ECMWF/CANADIAN COMPROMISE CONFIDENCE: ABOVE AVERAGE THE ENSEMBLE MEANS STRONG SUPPORT A DEEPER TRACK COMPARED TO THE 12Z NAM/GFS. TRENDS ARE INCONCLUSIVE...BUT GIVEN THE DEEPER SOLUTION SHOWN BY THE ENSEMBLE MEANS AND WPC CONTINUITY...WILL CONTINUE TO LEAN TOWARD THE DEEPER SIDE OF THE DETERMINISTIC GUIDANCE. THIS IS BEST REPRESENTED BY THE 00Z UKMET/ECMWF/CMC. SYSTEM DEPARTING FROM NEW ENGLAND THROUGH WED ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE GUIDANCE SHOWS GOOD AGREEMENT WITH THIS SYSTEM. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... OTTO