809  
FXUS10 KWNH 251647  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1146 AM 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 NAM/GFS EVALUATION...WITH PRELIMINARY 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: NON 00Z UKMET BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
WHILE MINOR DETAIL DIFFERENCES EXIST BETWEEN ALL OF THE  
MODELS...ONLY THE 00Z UKMET SHOWS SIGNIFICANTLY DIFFERENT FROM THE  
NAM/GFS/ECMWF/CMC IN THAT IT HAS A STRONGER 500 MB CORE OVER THE  
SOUTHEAST NOTICEABLE BY MON. A NON 00Z UKMET BLEND IS PREFERRED  
WITH THIS SYSTEM.  
 
...PAIR OF UPPER TROUGHS CROSSING THE NORTHEAST U.S. EARLY SUN AND  
EARLY MON...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 00Z ECMWF/CMC ARE SLIGHTLY FASTER AND 00Z UKMET SLIGHTLY  
SLOWER WITH THE FIRST TROUGH AXIS FOR SUN ACROSS THE  
NORTHEAST...BUT THE DIFFERENCES ARE RELATIVELY MINOR. THE MODELS  
SHOW SIMILARLY WITH THE SECOND TROUGH AXIS...SO OVERALL...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/00Z 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 AND THE ENSEMBLES SHOW GOOD AGREEMENT AND  
LITTLE CHANGES FROM THE PAST 3 CYCLES. THEREFORE...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 00Z  
UKMET IS TOWARD THE FASTER SIDE WITH THE UPPER TROUGH PROGRESSION  
BY MON MORNING ALTHOUGH ITS TIMING EVOLVES TOWARD THE MODEL  
CONSENSUS AS THE TROUGH REACHES HUDSON BAY EARLY NEXT WEEK. THE  
00Z CMC IS A BIT SLOWER WITH THE TROUGH AXIS...AWAY FROM THE  
BETTER ENSEMBLE AGREEMENT WHICH IS BEST REPRESENTED BY A 00Z  
ECMWF/12Z GFS BLEND.  
 
...SOUTHERN STREAM TROUGH AXIS/CLOSED LOW INTO THE SOUTHWEST MON  
AND INTO THE SOUTHERN PLAINS LATE TUE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON 00Z CMC 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.  
 
...POSITIVELY TILTED UPPER TROUGH AXIS AND ASSOCIATED COLD FRONT  
IMPACTING THE WEST COAST ON TUE...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 00Z 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. ENSEMBLE SPAGHETTI HEIGHT PLOTS SHOW THE 12Z GFS IDEA  
AS A MINORITY OF POSSIBILITIES...WITH THE 00Z ECMWF AND 12Z NAM  
ALIGNING BEST WITH THE BETTER ENSEMBLE CLUSTERING.  
 
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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