744  
FXUS10 KWNH 071842  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
142 PM EST SUN JAN 07 2018  
 
VALID JAN 07/1200 UTC THRU JAN 11/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION INCLUDING PREFERENCES AND FORECAST CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE DIGGING FROM THE FOUR CORNERS REGION TO THE NORTHERN  
GULF BY MONDAY WITH A CLOSED UPPER LOW DEVELOPING...  
...POSSIBLE WEAK EXTRATROPICAL SURFACE LOW DEVELOPING IN THE  
VICINITY OF FLORIDA BY TUESDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS/NAM...12Z GEFS...00Z ECMWF ENS MEAN  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
---18Z UPDATE---  
THE 12Z UKMET MADE SLIGHT ADJUSTMENTS TOWARD A WEAKER SOLUTION FOR  
THE MID-UPPER LEVEL LOW IN THE GULF. HOWEVER THE UKMET AND  
ESPECIALLY THE ECMWF CONTINUE TO SHOW A STRONGER LOW ALOFT THAN  
THE OTHER MODELS...AS WELL AS A WEAK SURFACE LOW DEVELOPING. WITH  
NO ADDITIONAL MODEL SUPPORT FOR THIS IDEA YET...WILL MAINTAIN THE  
PRELIMINARY PREFERENCE.  
 
---PREV. DISCUSSION---  
MODELS CONTINUE TO SHOW SOME DIVERGING SOLUTIONS OVER THE GULF OF  
MEXICO RELATED TO HOW STRONG THE UPPER LOW IS THAT DEVELOPS...AND  
HOW RESISTANT IT IS TO WEAKENING AS A RIDGE BUILDS IN QUICKLY TO  
THE NORTH AND CUTS IT OFF FROM THE STRONGER SYNOPTIC FLOW. THE 00Z  
ECMWF...AND TO A LESSER EXTENT THE 00Z UKMET...CONTINUES TO SHOW A  
STRONGER UPPER LEVEL LOW THAT LINGERS INTO MID-WEEK WITH A SURFACE  
LOW DEVELOPING IN THE VICINITY OF FLORIDA. THE OTHER MODELS  
DEVOLVE THE LOW MORE QUICKLY -- AGREEING THAT A BROAD TROUGH WILL  
BE IN PLACE OVER THE EASTERN GULF BUT WITH A WEAKER CIRCULATION  
ALOFT AND ONLY A TROUGH OR BRIEF LOW DEVELOPING AT THE SURFACE.  
GEFS/ECMWF ENSEMBLE CLUSTERS CONTINUE TO SHOW MORE SUPPORT FOR A  
WEAKER SOLUTION THAN THE OPERATIONAL ECMWF IS DEPICTING. A LIMITED  
NUMBER OF ECMWF ENSEMBLE MEMBERS DO SHOW A WELL-DEFINED SURFACE  
LOW...BUT MORE ARE IN LINE WITH THE OTHER MODEL SOLUTION DESCRIBED  
ABOVE. FOR THIS REASON...THE PREFERENCE IS FOR A BLEND OF THE 12Z  
GFS AND NAM...BUT ALSO TO INCLUDE THE ENSEMBLE MEANS WHICH HAVE  
SIMILAR POSITIONS AND PROGRESSION TO THE TROUGH AS THEIR  
OPERATIONAL COUNTERPARTS...BUT WITH A WEAKER DEPICTION OF THE LOW  
ALOFT.  
 
   
..LOW AMPLITUDE TROUGH MOVING NEAR THE U.S.-CANADA BORDER
 
 
...ACCOMPANYING SURFACE COLD FRONT SWEEPING ACROSS THE GREAT LAKES  
AND NORTHEAST TODAY AND MONDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
---18Z UPDATE---  
NO CHANGE TO THE PRELIMINARY PREFERENCE AS MODELS REMAIN IN FAIRLY  
GOOD AGREEMENT OVERALL.  
 
---PREV. DISCUSSION---  
MODELS CONTINUE TO BE IN GOOD AGREEMENT OVERALL WITH THIS SYSTEM  
AND ONLY SHOW MINOR DETAIL DIFFERENCES IN THE MASS FIELDS.  
THEREFORE A GENERAL MODEL BLEND CONTINUES TO BE THE PREFERENCE.  
 
   
..TROUGH APPROACHING THE WEST COAST BY MON MORNING
 
AND PUSHING  
THROUGH THE WEST AND INTO THE PLAINS BY WED...   
..SURFACE CYCLOGENESIS OVER THE PLAINS BY MIDWEEK
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: THROUGH 09/18Z (48HR) GENERAL MODEL BLEND  
AFTER 09/18Z -- BLEND OF 12Z GFS/NAM AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
---18Z UPDATE---  
THE 12Z UKMET/CMC HAVE TRENDED IN THE DIRECTION OF THE PRELIMINARY  
PREFERENCE MODELS (NAM/GFS/ECMWF) BEYOND 48 HOURS...BUT STILL DO  
HAVE SOME DIFFERENCES. IN PARTICULAR THEY PUSH HEIGHT FALLS  
THROUGH THE WEST FASTER AND ARE ALSO FURTHER NORTH WITH THE UPPER  
LEVEL LOW/VORT MAX AS IT KICKS INTO THE PLAINS.  
THEREFORE...DESPITE THE SMALLER SPREAD ON THE 12Z MODEL  
CYCLE...WILL MAINTAIN THE PRELIMINARY PREFERENCE OF A BLEND OF THE  
GFS/NAM/ECMWF.  
 
---PREV. DISCUSSION---  
OPERATIONAL MODELS ARE IN GOOD AGREEMENT WITH THE TIMING AND  
STRUCTURE OF THE TROUGH AS IT PUSHES INTO THE WEST COAST OVER THE  
NEXT DAY OR TWO...AND THEY ARE ALSO CLOSELY ALIGNED WITH ENSEMBLE  
MEANS. THIS LEADS TO HIGHER CONFIDENCE IN THE FORECAST OVER THOSE  
PARTICULAR DAYS AND A PREFERENCE FOR A GENERAL MODEL BLEND THROUGH  
TUESDAY MORNING.  
 
AFTER THAT POINT DIFFERENCES BEGIN TO EMERGE. THE 00Z UKMET IS  
MUCH QUICKER TO DEVOLVE THE CLOSED LOW INTO AN OPEN WAVE AND KICK  
IT NORTHEAST IN THE INTERMOUNTAIN WEST...AND BY THE TIME THE  
TROUGH ARRIVES IN THE PLAINS ITS PLACEMENT OF THE CYCLOGENESIS IS  
STRONGER AND FURTHER NORTHWEST THAN OTHER MODELS. THE 00Z CMC IS  
MORE SIMILAR IN THE LATITUDE OF THE STRONGEST PVA AND HEIGHT FALLS  
ALOFT...BUT SHOWS A SLIGHTLY SLOWER AND MORE POSITIVELY-TILTED  
TROUGH. PREFER A BLEND OF THE 12Z NAM...12Z GFS AND 00Z ECMWF  
WHICH ALL HAVE A (SLIGHT) NEGATIVE TILT TO THE TROUGH AS IT EJECTS  
INTO THE PLAINS...AS DOES THE 00Z ECMWF ENSEMBLE MEAN...AND THE  
TIMING OF THESE MODELS IS QUITE CLOSE.  
 
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