191  
FXUS10 KWNH 081900  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 PM 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 MODEL EVALUATION ALONG WITH FINAL 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: 12Z GFS / 12Z UKMET BLEND  
CONFIDENCE: AVERAGE  
 
THE 12Z AND 00Z ECMWF...AND TO A LESSER EXTENT THE 00Z  
UKMET...APPEAR 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...ALTHOUGH THE ECMWF HAS BEEN TRENDING WEAKER  
WITH THIS FEATURE SINCE YESTERDAY. ENSEMBLE SUPPORT FOR A DEFINED  
SURFACE LOW IS STILL RATHER POOR AND MAINLY FROM ECMWF MEMBERS.  
THE 12Z NAM DOES NOT SHOW THE RETURNING SURFACE BOUNDARY VERY WELL  
BUT THE 12Z CMC NOW SHOWS IT COMPARED TO ITS PREVIOUSLY MORE ILL  
DEFINED RUN. DIFFERENCES BETWEEN THE 12Z GFS AND 12Z UKMET ARE  
WITH TIMING...THE 12Z GFS IS SLOWER. A BLEND BETWEEN THESE TWO  
MODELS WITH SIMILAR STRENGTHS BUT DIFFERING TIMING APPEARS TO BEST  
ROUTE AT THIS TIME REGARDING 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: 50/50 BLEND OF 12Z GFS WITH THE 00Z OR 12Z ECMWF  
(READ BELOW FOR DETAILS)  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
DIFFERENCES BECOME MOST SIGNIFICANT AS THE SYSTEM REACHES THE  
PLAINS WED EVENING. THE TIMING OF THE UPPER TROUGH AND SURFACE  
FRONT IN THE 12Z NAM IS FASTEST AND THE 12Z GFS ALSO APPEARS A BIT  
QUICKER 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 12Z NAM/GFS AND THE 00Z ECMWF MEAN WITH THE 500 MB TROUGH  
AXIS WED EVENING. HOWEVER...THE 12Z ECMWF/UKMET/CMC ALL TRENDED  
SLOWER COMPARED TO THEIR 00Z CYCLES VALID 00Z/11 AS THE 500 MB  
TROUGH AXIS REACHES THE PLAINS. RUN TO RUN CONSISTENCY HAS BEEN  
RATHER POOR IN THE MODELS WHICH LOWERS CONFIDENCE.  
 
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 SLIGHTLY  
BELOW AVERAGE CONFIDENCE CONSIDERING RUN TO RUN CHANGES IN ALL OF  
THE DETERMINISTIC GUIDANCE SEEN IN THE 12Z CYCLE AND ABOVE AVERAGE  
ENSEMBLE SPREAD. GIVEN THE TRENDS SEEN IN THE 12Z  
ECMWF/UKMET/CMC...A 50/50 BLEND OF THE FASTER 12Z GFS AND SLOWER  
00Z ECMWF APPEARS BEST FOR THE TIMING OF THE UPPER WAVE...BUT THE  
12Z ECMWF DOES APPEAR TO BE AN IMPROVEMENT WITH THE SURFACE WAVE  
NEARING THE GREAT LAKES REGION ON THU. EITHER THE 00Z/12Z ECMWF  
CAN BE BLENDED WITH THE 12Z GFS REGARDING THE 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: GENERAL MODEL 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 DETERMINISTIC GUIDANCE IS LIKELY BEST FOR THIS SYSTEM  
WITH INDIVIDUAL MODEL DIFFERENCES IN TIMING/DEPTH AS THE UPPER  
TROUGH REACHES THE PACIFIC NORTHWEST COAST.  
 
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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