496  
FXUS10 KWNH 191707  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
107 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 NAM/GFS EVALUATION ALONG WITH PRELIMINARY 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 00Z 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 00Z 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 00Z ECMWF CLOSEST TO THE MIDDLE OF THE SPREAD. THE 00Z  
UKMET IS NEXT CLOSEST TO THE 00Z ECMWF. THE SOUTHERN PORTION OF  
THE TROUGH REACHING TEXAS/OKLAHOMA IS SIMILARLY WEAK IN THE 12Z  
NAM/GFS...AND STRONGER IN THE 00Z ECMWF/UKMET/CMC. THE 00Z CMC IS  
BY FAR THE STRONGEST WITH THE SOUTHERN STREAM PORTION OF THE UPPER  
WAVE...WITH AGAIN...THE 00Z ECMWF/UKMET FALLING CLOSER TO THE  
MIDDLE OF THE SPREAD...WITH PERHAPS SHOWING SLIGHTLY TOWARD THE  
SLOW SIDE OF THE AVAILABLE MEMBERS. THE PREFERENCE WILL CONTINUE  
WITH CONTINUITY AT 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 IN WIND  
DIRECTION AND MOISTURE AXIS. CURRENTLY THE 12Z NAM APPEARS A  
FAVORABLE MIDDLE GROUND WITH THE AMPLITUDE OF THIS  
WAVE...SPLITTING THE DIFFERENCE BETWEEN THE MORE AMPLIFIED 00Z  
ECMWF AND FLATTER 12Z GFS. THERE WAS NO CLEAR CONSENSUS SEEN THE  
ENSEMBLE GUIDANCE WITH THIS SYSTEM.  
 
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