150  
FXUS10 KWNH 251843  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
143 PM EST SAT NOV 25 2017  
 
VALID NOV 25/1200 UTC THRU NOV 29/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...WITH FINAL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SURFACE LOW TRACKING NORTH THROUGH THE WESTERN ATLANTIC THIS  
WEEKEND...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS FEATURE.  
 
...BROAD UPPER TROUGHING OVER THE EASTERN GULF OF MEXICO THROUGH  
TUE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
WHILE MINOR DETAIL DIFFERENCES EXIST BETWEEN ALL OF THE  
MODELS...TRENDS IN THE 12Z UKMET FROM ITS 00Z RUN IS TOWARD THE  
MODEL CONSENSUS SO A GENERAL MODEL BLEND CAN BE USED FOR THIS  
SYSTEM.  
 
...PAIR OF UPPER TROUGHS CROSSING THE NORTHEAST U.S. EARLY SUN AND  
EARLY MON...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z DETERMINISTIC GUIDANCE HAS CONVERGED CLOSER TOWARD ONE  
ANOTHER REGARDING UPPER TROUGH TIMING AND AMPLITUDE. ANY REMAINING  
DIFFERENCES ARE RELATIVELY MINOR SO A GENERAL MODEL BLEND CAN BE  
USED FOR THIS AREA OF THE COUNTRY.  
 
   
..LOW PRESSURE LIFTING UP OFF THE WEST COAST TONIGHT
 
   
..DEEP UPPER TROUGH OFFSHORE THE WEST COAST THROUGH SUN
 
 
...NORTHERN STREAM TROUGH AXIS AND ASSOCIATED SURFACE LOW/COLD  
FRONT ACROSS SOUTHERN CANADA ON MON AND HUDSON BAY ON TUE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS/12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THERE ARE ONLY MINOR DIFFERENCES WITH THE POSITION AND STRENGTH OF  
THE SURFACE LOW FORECAST TO MOVE NORTHWARD TO THE WEST OF  
VANCOUVER ISLAND TONIGHT WITH THE 12Z NAM FARTHEST EAST AND 12Z  
CMC FARTHEST WEST. AGREEMENT IS CLOSE ENOUGH AND GIVEN THE  
ENSEMBLES SHOW GOOD AGREEMENT AND LITTLE CHANGES FROM THE PAST 3  
CYCLES...A GENERAL MODEL BLEND IS PREFERRED FOR THE SURFACE LOW  
TRACK.  
 
AS THE LARGE UPPER TROUGH APPROACHING THE WEST COAST TOMORROW  
MOVES EASTWARD...IT IS EXPECTED TO SPLIT WITH THE NRN STREAM  
PORTION TRACKING EAST THROUGH SOUTHERN CANADA MON/TUE. THE 12Z  
UKMET SLOWED FROM ITS PREVIOUSLY FASTER UPPER TROUGH PROGRESSION  
BY MON MORNING AND IS NOW ONLY SLIGHTLY FASTER THAN THE REMAINING  
MODELS ALTHOUGH ITS TIMING EVOLVES TOWARD THE MODEL CONSENSUS AS  
THE TROUGH REACHES HUDSON BAY EARLY NEXT WEEK. THE 12Z CMC REMAINS  
A BIT SLOWER WITH THE TROUGH AXIS...AWAY FROM THE BETTER ENSEMBLE  
AGREEMENT WHICH IS BEST REPRESENTED BY A 12Z ECMWF/12Z GFS BLEND.  
 
...SOUTHERN STREAM TROUGH AXIS/CLOSED LOW INTO THE SOUTHWEST MON  
AND INTO THE SOUTHERN PLAINS LATE TUE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 12Z UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE ENSEMBLES WHICH WERE TRENDING SLOWER THROUGH FRI HAVE TRENDED  
FASTER OVER THE PAST 3 CYCLES LEAVING THE 00Z CMC AS AN OUTLIER  
EXCEPT FOR THE SLOWER 00Z CMC ENSEMBLE MEMBERS. GIVEN THERE IS  
BETTER ENSEMBLE AGREEMENT TODAY COMPARED TO YESTERDAY AS SEEN IN  
THE SPAGHETTI PLOTS...THE 00Z CMC IS THOUGHT TO HAVE A LOW  
PROBABILITY SOLUTION. WHILE THERE IS STILL SOME ROOM TO SLOW  
AGAIN...PERHAPS NEAR THE 00Z UKMET...THE IDEA FOR A FASTER TRACK  
LIKE THE NON 00Z CMC CONSENSUS IS STRONG.  
 
19Z UPDATE: THE 12Z CMC SPED UP TO THE REMAINING DETERMINISTIC  
CONSENSUS BUT THE 12Z UKMET NOW APPEARS TOO FAST GIVEN ITS  
PLACEMENT ON THE FAR EDGE OF ENSEMBLE MEMBERS BY 00Z/29. IT NOW  
APPEARS THAT A NON 12Z UKMET BLEND OF MODELS IS BEST FOR THIS  
SYSTEM.  
 
...POSITIVELY TILTED UPPER TROUGH AXIS AND ASSOCIATED COLD FRONT  
IMPACTING THE WEST COAST ON TUE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z ECMWF/12Z NAM BLEND  
CONFIDENCE: AVERAGE  
 
DIFFERENCES WITH THIS SYSTEM RELATE TO INTERACTION OF THE NORTHERN  
AND SOUTHERN PORTIONS OF THE TROUGH AXIS AS IT NEARS THE WEST  
COAST ON TUE. THE 12Z GFS HAS TRENDED TOWARD THE IDEA OF MORE  
SEPARATION BETWEEN THE TWO PORTIONS OF THE TROUGH CAUSING THE  
NORTHERN PORTION TO BE QUICKER TO PUSH INLAND ACROSS THE PACIFIC  
NORTHWEST ON TUE. ENSEMBLE SPAGHETTI HEIGHT PLOTS SHOW THE 12Z GFS  
IDEA AS A MINORITY OF POSSIBILITIES...WITH THE 12Z ECMWF AND 12Z  
NAM ALIGNING BEST WITH THE BETTER ENSEMBLE CLUSTERING. THE 12Z  
UKMET TROUGH AXIS BECOMES NEUTRAL TO NEGATIVELY TILTED BY 00Z/29  
WHICH IS UNSUPPORTED IN THE REMAINING GUIDANCE. MEANWHILE...THE  
12Z CMC IS SLOWER WITH THE TROUGH AXIS INTO THE NORTHWEST COMPARED  
TO THE REMAINING MODELS.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
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