MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 243 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: 12Z 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 12Z CMC COMPROMISE CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z CANADIAN REMAINS 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 12Z 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 / 12Z 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 12Z ECMWF/UKMET/CMC BUT THERE HAS BEEN SOME SLIGHTL CONVERGENCE TOWARD THE MIDDLE BY THE 12Z ECMWF/UKMET/CMC. THE NAM/GFS REMAIN MORE DEFINED WITH THE SHORTWAVE AS IT REACHES THE SOUTHEAST THU MORNING. THE INDIVIDUAL MODELS HAVE BEEN LARGELY 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: 12Z UKMET / 12Z NAM BLEND CONFIDENCE: BELOW AVERAGE THE 12Z 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 WAS ONE OF THE FASTER MODELS BUT SLOWED TOWARD THE REMAINING NON NAM/CMC CONSENSUS. BY 00Z/21...THE 00Z ECWMF ENSEMBLE MEMBERS ARE NORTH OF THE 00Z GEFS...WHICH CORRESPONDS SIMILARLY WITH THE 12Z 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 12Z UKMET APPEARS REASONABLE WITH THE TIMING OF THE SHORTWAVE...DESPITE A NRN JOG IN THE 12Z RUN WITH THE COASTAL LOW. THE 12Z UKMET SPLITS THE NORTH/SOUTH DIFFERENCE WITH THE POSITION OF THE MID-ATLANTIC COASTAL LOW...AND IS MATCHED SOME 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: 12Z 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 12Z 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