MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 243 PM EDT THU SEP 03 2015 VALID SEP 03/1200 UTC THRU SEP 07/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM/GFS/UKMET/CMC AND ECMWF ...VORT LIFTING FROM THE CENTRAL ROCKIES TO THE NORTHERN PLAINS... PREFERENCE: 12Z ECMWF CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW GOOD AGREEMENT IN LIFTING A VORT CENTER OVER CO OFF TO THE NORTHEAST OVER THE NEXT 24 TO 36 HOURS AND ACROSS THE NORTHERN PLAINS. THERE ARE SOME MODEST DIFFERENCES WITH THE VORT INTENSITY AS IT LIFTS THROUGH THE NORTHERN PLAINS. THE 12Z GFS OVERALL IS THE WEAKEST SOLUTION...WITH THE 12Z NAM THE STRONGEST. THE 12Z ECMWF/12Z UKMET AND 12Z CMC SPLIT THE DIFFERENCE...BUT THE ECMWF REPRESENTS ESSENTIALLY THE GLOBAL MODEL CONSENSUS AND THIS WILL BE THE PREFERENCE. ...NEGATIVELY-TILTED TROUGH CROSSING THE NORTHWEST... PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z NAM AND 12Z CMC TEND TO BE STRONGER OUTLIERS ALOFT WITH THE EVOLVING DEEP TROUGH THAT GOES NEG-TILT ACROSS THE NORTHWEST AND OUT INTO THE HIGH PLAINS OVER THE NEXT TWO TO THREE DAYS. THE 12Z UKMET APPEARS TO BE A TAD TOO STRONG AT THE SURFACE WITH THE DEEPENING LOW CENTER. THE STRONGER MODEL CLUSTERING TENDS TO FAVOR THE 12Z GFS AND 12Z ECMWF WHICH IS A TAD WEAKER THAN THE NAM AND CMC SOLUTIONS...AND SO A BLEND OF THESE SOLUTIONS WILL BE PREFERRED. ...MID LEVEL TROUGH/CLOSED LOW CENTER OVER MI... PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF CONFIDENCE: ABOVE AVERAGE A RATHER COMPACT MID LEVEL TROUGH AND ASSOCIATED CLOSED LOW OVER LOWER MI IS EXPECTED TO LINGER HERE OVER THE NEXT COUPLE OF DAYS BEFORE THEN WEAKENING THIS WEEKEND AND GRADUALLY SHEARING THROUGH SOUTHEAST ONTARIO. THE 12Z NAM AND 12Z CMC TEND TO HANG ONTO SOMEWHAT STRONGER HEIGHT FALLS WITH THIS SYSTEM BEFORE GRADUALLY WEAKENING THE ENERGY. OVERALL...THE MODEL SPREAD IS NOT PARTICULARLY SIGNIFICANT...BUT WILL AGAIN SUGGEST A BLEND OF THE 12Z GFS AND 12Z ECMWF GIVEN BETTER OVERALL CLUSTERING AND ENSEMBLE SUPPORT. ...RETROGRADING UPPER LOW MOVING INTO THE SOUTHEAST SAT/SUN... PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF AND 12Z UKMET CONFIDENCE: AVERAGE THE MODELS INDICATE DEVELOPMENT OF A REX BLOCK ALONG AND JUST OFFSHORE THE EAST COAST BY SAT. THE UPPER LOW DEVELOPING OFF THE SOUTHEAST COAST IS FORECAST TO SLOWLY RETROGRADE INTO THE INTERIOR SOUTHEAST BY LATE SUN. SURFACE LOW PRESSURE ASSOCIATED WITH THIS APPEARS IN PART TO BE RELATED TO THE REMNANTS OF FORMER T.S. ERIKA. THE 12Z CMC OVERALL IS THE DEEPEST SOLUTION WITH THE EVOLUTION OF ALL OF THIS ENERGY. THE 12Z GFS/12Z ECMWF AND 12Z UKMET ARE ALL A LITTLE WEAKER ALOFT AND WITH THE SURFACE PRESSURE FIELDS. THE 12Z NAM APPEARS TO BE TOO FAR EAST WITH ITS SURFACE AND MID LEVEL LOW CENTERS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON