262  
FXUS10 KWNH 061828  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
128 PM EST SAT JAN 06 2018  
 
VALID JAN 06/1200 UTC THRU JAN 10/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..SOUTHERN BRANCH OF SPLITTING TROUGH ALONG WEST COAST
 
 
...SHORTWAVE DIGGING FROM NRN CA TODAY TO THE GULF COAST BY MONDAY  
WITH POSSIBLE CLOSED UPPER LOW DEVELOPING OVER THE GULF...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z NAM / 12Z CMC  
CONFIDENCE: AVERAGE  
 
---18Z UPDATE---  
THE NEW 12Z ECMWF HAS REDUCED THE SIZE AND INTENSITY OF THE UPPER  
LEVEL LOW OVER THE GULF OF MEXICO...WHICH IS A TREND TOWARD THE  
PRELIMINARY PREFERENCE (AND THE NON-ECMWF CONSENSUS FROM THE  
PREVIOUS MODEL CYCLE). HOWEVER...IT STILL SHOWS A WELL-DEFINED  
UPPER LEVEL LOW AND ASSOCIATED EXTRATROPICAL CYCLOGENESIS OVER THE  
WESTERN CARIBBEAN BY TUESDAY NIGHT. ALTHOUGH MANY MODELS DO SHOW A  
WEAK SURFACE WAVE...THEY DO NOT DEVELOP THE SURFACE LOW TO THE  
EXTENT THAT THE ECMWF DOES. THE 12Z UKMET NOW SHOWS A STRONGER  
UPPER LEVEL LOW...BUT DOES NOT HAVE AS STRONG A SURFACE REFLECTION  
AS THE ECMWF. THE FINAL PREFERENCE IS FOR A BLEND OF THE  
GFS/NAM/CMC.  
 
---PREV. DISCUSSION---  
MODELS ARE IN EXCELLENT AGREEMENT WITH THE PROGRESSION OF THE  
SHORTWAVE TROUGH THROUGH SUNDAY EVENING WHEN IT SHOULD EMERGE INTO  
THE PLAINS. DIFFERENCES THEN EMERGE AS THIS SOUTHERN STREAM WAVE  
CONTINUES TO DIG INTO THE GULF OF MEXICO OVER THE SUBSEQUENT  
COUPLE DAYS. MANY OF THE AVAILABLE MODELS NOW SHOW A CLOSED UPPER  
LEVEL LOW DEVELOPING OVER THE GULF OF MEXICO ON MONDAY NIGHT AND  
TUESDAY. THE TREND HAS BEEN TOWARD A SHARPER DIG TO THE TROUGH  
WITH A POSITION FURTHER WEST AND THE POTENTIAL FOR A CLOSED  
LOW...SO THAT SEEMS REASONABLE. AS RIDGING BUILDS IN OVER THE TOP  
OF THE UPPER LOW INTO THE CENTRAL AND EASTERN U.S. AND IT BECOMES  
INCREASINGLY CUT OFF FROM STRONGER FLOW...THE LOW SHOULD GRADUALLY  
WEAKEN.  
 
THE 00Z ECMWF HAS THE STRONGEST DEPICTION OF THE UPPER LEVEL LOW  
AND MAINTAINS A FAIRLY STRONG LOW WELL AFTER THE RIDGE BEGINS  
BUILDING IN TO THE NORTH. THIS IS SUPPORTED BY ONLY A SMALL  
PERCENTAGE OF THE GEFS/EC ENSEMBLE CLUSTERS...AND SEEMS TO FIT THE  
SYNOPTIC PATTERN LESS THAN OTHER MODELS. THEREFORE...IT IS  
EXCLUDED FROM THE PREFERENCE AT THIS TIME.  
 
DIFFERENCES EXIST WITH THE OTHER MODELS IN THE EXACT POSITION OF  
THE LOW...BUT IN GENERAL THEY SHOW SIMILAR AMPLITUDE OF THE  
OVERALL WAVE AND INTENSITY AT THE CORE OF THE UPPER LEVEL LOW.  
THEREFORE A NON-ECMWF BLEND IS THE PREFERENCE AT THIS TIME.  
 
   
..NORTHERN BRANCH OF SPLITTING TROUGH ALONG WEST COAST
 
 
...MOVING THROUGH THE CANADIAN ROCKIES THIS WEEKEND AND THEN  
DIGGING TO NEAR THE GREAT LAKES BY MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
---18Z UPDATE---  
MODELS REMAIN IN GOOD AGREEMENT SO THERE IS NO CHANGE.  
 
---PREV. DISCUSSION---  
OPERATIONAL MODELS ARE IN CLOSE AGREEMENT ON THE TIMING AND  
AMPLITUDE OF THIS WAVE AS IT PUSHES NEAR OR ACROSS THE NORTHERN  
TIER OF STATES. LIMITED SPREAD IN THE MASS FIELDS LEADS TO A  
PREFERENCE OF A GENERAL MODEL BLEND WITH ABOVE AVERAGE CONFIDENCE.  
 
...NEXT UPPER LEVEL TROUGH OVER THE EASTERN PACIFIC APPROACHING  
THE WEST COAST SUNDAY NIGHT INTO MONDAY...  
...UPPER LOW CLOSING OFF AT THE BASE OF THE TROUGH AND MOVING INTO  
THE SOUTHWEST ON TUESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS / 12Z ECMWF / 12Z UKMET  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
---18Z UPDATE---  
THE 12Z CMC NOW SHOWS AN OPEN WAVE PROGRESSING INTO THE WEST  
COAST...WHICH IS AT ODDS WITH THE OTHER MODELS. EVEN THE WEAKER  
AND FASTER NAM STILL HAS A SMALL CLOSED LOW FOR A PORTION OF THE  
FORECAST PERIOD. OTHERWISE...THE UKMET...GFS...AND ECMWF  
MAINTAINED A FAIR DEGREE OF CONTINUITY WITH THIS MODEL CYCLE...AND  
THE PREFERENCE IS NOW FOR A BLEND OF THOSE THREE MODELS.  
 
---PREV. DISCUSSION---  
MODELS HAVE CONVERGED ON THEIR DEPICTION OF THE TROUGH APPROACHING  
THE WEST COAST OVER THE PAST SEVERAL MODEL CYCLES AND NOW APPEAR  
TO BE IN FAIRLY GOOD AGREEMENT...INCLUDING THE FORMATION OF A  
CLOSED LOW AT THE BASE OF THE TROUGH WHICH SHOULD THEN PUSH INTO  
CTRL/SRN CALIFORNIA. THE PRIMARY DIFFERENCE IS WITH THE 12Z NAM  
WHICH DOES NOT DIG THE TROUGH AS MUCH AS THE OTHER MODELS AND AS A  
RESULT HAS A FASTER TROUGH AXIS WITH A WEAKER EMBEDDED LOW WHEN IT  
ARRIVES IN CA/NV ON TUESDAY. THEREFORE...IT WAS EXCLUDED FROM THE  
PREFERENCE FOR THIS SYSTEM. OTHER MODELS DO SHOW SOME MINOR TIMING  
DIFFERENCES...BUT ALL HAVE THE LOW AT APPROXIMATELY THE SAME  
LATITUDE AND A SIMILAR STRUCTURE TO THE SYSTEM. THEREFORE THE  
PREFERENCE IS FOR A NON-NAM BLEND.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page