227  
FXUS10 KWNH 081659  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1158 AM EST MON JAN 08 2018  
 
VALID JAN 08/1200 UTC THRU JAN 12/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z NAM/GFS EVALUATION ALONG WITH PRELIMINARY PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...MID-LEVEL SHORTWAVE/CLOSED LOW TRACKING INTO THE ERN GULF OF  
MEXICO BY TUE MORNING...  
...POSSIBLE SURFACE LOW NEAR OR EAST OF FL WITH POTENTIAL COASTAL  
BOUNDARY ALONG THE SOUTHEAST COAST...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NEAR THE 12Z GFS  
CONFIDENCE: AVERAGE  
 
THE 00Z ECMWF...AND TO A LESSER EXTENT THE 00Z UKMET...APPEARS TO  
BE HOLDING ONTO A STRONGER SURFACE LOW IN THE VICINITY OF A  
RETREATING FRONTAL BOUNDARY EAST OF THE FL PENINSULA ON WED/WED  
NIGHT. ENSEMBLE SUPPORT FOR A DEFINED SURFACE LOW IS STILL RATHER  
POOR AND MAINLY FROM ECMWF MEMBERS. THE 12Z NAM AND 00Z CMC DO NOT  
SHOW THE RETURNING SURFACE BOUNDARY VERY WELL SO IT APPEARS THE  
12Z GFS IS CLOSEST TO WHAT IS CONSIDERED THE BEST MODEL FOR THIS  
SYSTEM.  
 
...UPPER TROUGH TRANSLATING ACROSS THE GREAT LAKES TODAY/NORTHEAST  
EARLY TUE MORNING...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS SHOW SIMILARLY WITH THIS SYSTEM.  
 
...UPPER TROUGH APPROACHING THE WEST COAST EARLY TUE MORNING WITH  
RESULTING CYCLOGENESIS IN THE SRN/CNTRL PLAINS WED-THU...  
...FRONTAL BOUNDARY AND SURFACE WAVES INTO THE PLAINS/MS RIVER  
VALLEY FOR WED/THU...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 2/3 WEIGHT 12Z GFS...1/3 WEIGHT 00Z ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
DIFFERENCES BECOME MOST SIGNIFICANT AS THE SYSTEM REACHES THE  
PLAINS. THE TIMING OF THE UPPER TROUGH AND SURFACE FRONT IN THE  
12Z NAM IS FASTEST AND THE 12Z GFS ALSO APPEARS A BIT TOO QUICK  
WITH THE 12Z GFS TRENDING FASTER OVER THE PREVIOUS 00Z AND 12Z  
CYCLES. THE 00Z ECMWF ON THE OTHER HAND IS SLOWER...SLOWER THAN  
THE DETERMINISTIC CONSENSUS AND THE 00Z ECMWF MEAN. THE 00Z  
UKMET/CMC DO NOT MATCH THE 500 MB PATTERN AS WELL TO THE LATEST  
ENSEMBLE MEANS AND WITH THEIR SURFACE LOWS.  
 
AN EYEBALL APPROACH OF THE GREATEST DENSITY SEEN IN ENSEMBLE  
SPAGHETTI HEIGHTS IS A BLEND BETWEEN THE 12Z GFS AND 00Z ECMWF  
WITH MORE WEIGHT TOWARD THE 12Z GFS FOR THIS SYSTEM WITH ONLY  
AVERAGE CONFIDENCE CONSIDERING RUN TO RUN CHANGES IN ALL OF THE  
DETERMINISTIC GUIDANCE AND ABOVE AVERAGE ENSEMBLE SPREAD. THIS  
ALSO APPLIES TO THE SURFACE WAVE ALONG THE FRONT MOVING INTO THE  
GREAT LAKES REGION ON THU AND POSSIBLE WAVE IN THE VICINITY OF THE  
LOWER MS VALLEY ON THU GIVEN THE LATEST ENSEMBLE SCATTER LOW PLOT.  
 
...QUICK MOVING SHORTWAVE FORECAST TO REACH THE PACIFIC NORTHWEST  
ON THU...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM...12Z GFS...00Z ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
TIMING DIFFERENCES ARE MODERATE WITH THE LATEST MODELS...BUT THE  
LATEST ENSEMBLE MEANS SHOW DECENT AGREEMENT. THEREFORE...A BLEND  
OF THE 12Z NAM...12Z GFS...00Z ECMWF ARE PREFERRED GIVEN THEIR  
BLENDED AVERAGE IS NEAREST TO THE ENSEMBLE MEANS.  
 
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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