618  
FXUS10 KWNH 191844  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
243 PM EDT THU OCT 19 2017  
 
VALID OCT 19/1200 UTC THRU OCT 23/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION ALONG WITH FINAL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..SHORTWAVE CLIPPING NORTHERN NEW ENGLAND BY THURS EVENING
 
   
..ASSOCIATED COLD FRONT CROSSING THE NORTHEAST BY WEEKS END
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
   
..ONGOING ATMOSPHERIC RIVER EVENT INTO THE WEST COAST
 
   
..LONGWAVE TROUGH EVOLUTION INTO THE WESTERN U.S. THROUGH FRI
 
   
..EJECTING OUT INTO THE PLAINS ON SAT ALONG WITH COLD FRONT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z UKMET/ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT THROUGH FRIDAY WITH THE EVOLUTION  
OF THE LONGWAVE TROUGH AND ASSOCIATED COLD FRONT MOVING THROUGH  
THE WESTERN U.S. BUT DIFFERENCES GROW OVER THE WEEKEND. THE 12Z  
NAM/GFS CONTINUE THEIR IDEA FOR A STRONGER NRN PORTION OF THE  
TROUGH AXIS WHICH MOVES INTO SOUTH-CENTRAL CANADA SATURDAY  
NIGHT...WHEREAS THE 12Z ECMWF/UKMET/CMC ARE LESS STRONG HERE.  
 
ENSEMBLE SPAGHETTI PLOTS CONTINUE TO SHOW THE NAM/GFS IDEA IS TOO  
EXTREME LYING ON THE FAR EDGES OF THE DEEPEST ENSEMBLE MEMBERS  
WITH THE 12Z ECMWF/UKMET CLOSEST TO THE MIDDLE OF THE SPREAD. THE  
SOUTHERN PORTION OF THE TROUGH REACHING TEXAS/OKLAHOMA IS  
SIMILARLY WEAK IN THE 12Z NAM/GFS...AND STRONGER IN THE 12Z  
ECMWF/UKMET/CMC WHILE THE 12Z CMC IS FASTEST WITH THE SOUTHERN  
STREAM PORTION OF THE UPPER WAVE. ADJUSTMENTS MADE BY THE 12Z  
ECMWF TO BE FASTER...AND SLIGHTLY FASTER IN THE 12Z UKMET...NOW  
SHOW THE ECMWF/UKMET MUCH CLOSER TO THE MIDDLE OF THE ENSEMBLE  
SPREAD. THE PREFERENCE WILL CONTINUE WITH A 12Z ECMWF/UKMET BLEND  
THE MOMENT FOR THIS SYSTEM.  
 
   
..SOUTHERN STREAM UPPER TROUGH REACHING THE SOUTHERN PLAINS FRI
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT WITH THIS SYSTEM...SO A GENERAL  
MODEL COMPROMISE WILL BE PREFERRED.  
 
   
..SHORTWAVE REACHING BRITISH COLUMBIA LATE SAT WITH WARM FRONT
 
   
..NEXT ATMOSPHERIC RIVER ARRIVING OVER THE PACIFIC NORTHWEST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NEAR THE 12Z NAM  
CONFIDENCE: AVERAGE  
 
DIFFERENCES WITH THIS SYSTEM PERTAIN TO THE AMPLITUDE OF THE  
MID-LEVEL WAVE AS IT NEARS THE PACIFIC NORTHWEST. THESE  
DIFFERENCES IN THE MID-LEVEL HEIGHTS ARE RELATIVELY MINOR BUT  
GREATER IMPACTS ARE SEEN IN THE LOW LEVEL REFLECTION FOR WIND  
DIRECTION AND THE MOISTURE AXIS. CURRENTLY THE 12Z NAM APPEARS A  
FAVORABLE MIDDLE GROUND WITH THE AMPLITUDE OF THIS  
WAVE...SPLITTING THE DIFFERENCE BETWEEN THE MORE AMPLIFIED ECMWF  
AND FLATTER 12Z GFS. THERE WAS NO CLEAR CONSENSUS SEEN THE  
ENSEMBLE GUIDANCE WITH THIS SYSTEM. 12Z ECMWF/UKMET/CMC  
ADJUSTMENTS WERE SMALL BUT IN THE DIRECTION OF THE MIDDLE GROUND  
12Z NAM SO THE FINAL PREFERENCE REMAINS UNCHANGED FROM THE  
PRELIMINARY.  
 
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