754  
FXUS10 KWNH 101633  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1132 AM EST SAT FEB 10 2018  
 
VALID FEB 10/1200 UTC THRU FEB 14/0000 UTC  
 
   
..SEE NOUS42 KWNO (ADMNFD) FOR STATUS OF THE UPPER AIR INGEST
 
 
   
..12Z MODEL EVALUATION WITH PRELIMINARY PREFERENCES/CONFIDENCE
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE MOVING THROUGH THE CENTRAL ROCKIES TODAY AND GETTING  
SHEARED OUT OVER MID-MISSISSIPPI VALLEY SUNDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-NAM BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE 12Z NAM CONTINUES TO EJECT THE SHORTWAVE A LITTLE FASTER THAN  
THE OTHER MODELS, WHICH WAS ALSO THE CASE YESTERDAY. OTHER MODELS  
HAVE COME INTO MUCH BETTER AGREEMENT AND OFFER VERY LITTLE  
DIFFERENCE IN THE TIMING OR AMPLITUDE OF THE SHORTWAVE, AS WELL AS  
THE POSITION OR INTENSITY OF THE ASSOCIATED SURFACE LOW OVER  
NORTHERN NEW MEXICO. THEREFORE, THE PREFERENCE IS FOR A GENERAL  
MODEL BLEND THAT EXCLUDES THE 12Z NAM.  
 
...EXTENSIVE FRONT STRETCHING FROM THE SOUTHERN US NORTHEASTWARD  
INTO NEW ENGLAND AND BROAD SOUTHWESTERLY FLOW ALOFT...   
..WEAK SURFACE LOW DEVELOPMENT ALONG FRONT INTO SUNDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
A SUBTLE WAVE EJECTING IN THE BROAD SOUTHWESTERLY FLOW APPEARS TO  
BE SOMEWHAT STRONGER THAN MODELS WERE ANTICIPATING SEVERAL MODEL  
CYCLES AGO. THIS WAS THE WAVE THAT WAS EXPECTED TO CONTRIBUTE TO  
SLOW AND WEAK SURFACE CYCLOGENESIS ALONG THE ELONGATED FRONT FROM  
THE CENTRAL APPALACHIANS INTO THE NORTHEAST. MODELS HAVE NOW  
TRENDED TOWARD A MORE PRONOUNCED (ALBEIT STILL FAIRLY WEAK)  
SURFACE LOW, DEVELOPING BY THIS EVENING OVER MIDDLE TENNESSEE, AND  
THEN SHIFTING NORTHEAST TO THE ST. LAWRENCE VALLEY BY TOMORROW  
EVENING. IN ADDITION TO THIS TREND, MODEL SPREAD HAS BEEN  
SUBSTANTIALLY REDUCED, AND FOR THIS REASON A GENERAL MODEL BLEND  
IS PREFERRED. THE MASS FIELDS FROM ALL THE GLOBAL MODELS AND THE  
NAM LOOK REASONABLY SIMILAR OVERALL.  
 
   
..SHORTWAVE DIGGING INTO THE PACIFIC NORTHWEST ON SUNDAY
 
   
..POSITIVE TILT TROUGH BUILDING DOWN THE WEST COAST MONDAY
 
   
..CLOSED LOW DEVELOPING NEAR THE CALIFORNIA COAST TUESDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF 12Z GFS, NAM AND 00Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MOST NOTABLE MODEL TREND OVER THE PAST SEVERAL MODEL CYCLES IS  
THAT THERE IS GOOD AGREEMENT NOW ON DIGGING THE SHORTWAVE MORE  
SHARPLY ALONG THE WEST COAST AFTER IT FINISHES UNDERCUTTING A  
NORTHWARD EXTENSION OF THE EAST PACIFIC RIDGE. MOST MODELS NOW  
BRING THE CORE OF THE TROUGH INTO THE OREGON COAST AROUND 44N,  
WHICH IS MUCH FURTHER SOUTH THAN 3-4 MODEL CYCLES AGO.  
 
DESPITE THE SHARP DIGGING OF THE TROUGH, THE 00Z CMC DEPICTS A  
TROUGH THAT IS MUCH BROADER THAN OTHER MODELS BY 12/00Z, AND HAS  
HIGHER HEIGHTS THROUGH MUCH OF THE WESTERN CONUS AHEAD OF THE  
TROUGH. ALTHOUGH IT EVENTUALLY CONVERGES TO BE CLOSER TO THE OTHER  
GLOBAL MODELS BY 13/00Z, THE INITIAL DIFFERENCES ARE SUBSTANTIAL  
ENOUGH TO EXCLUDE IT FROM THE PREFERENCE AT THIS TIME.  
 
THE OTHER MODEL THAT SHOWS MORE SUBSTANTIAL DIFFERENCES IS THE 00Z  
UKMET. MOST MODELS NOW HAVE A CLOSED LOW NEAR THE CALIFORNIA COAST  
BY TUESDAY, AND IN FACT EVEN THE GEFS AND ECMWF ENS MEANS HAVE A  
CLOSED LOW. HOWEVER, THE UKMET SHOWS A NARROWER AND MORE ELONGATED  
TROUGH AND NEVER CLOSES OFF A LOW AT 500MB. GIVEN THE OVERALL  
TREND TOWARD A CLOSED LOW AND THE SHARP DIGGING OF THE TROUGH  
ALONG THE WEST COAST, THE UKMET IS ALSO EXCLUDED FROM THE  
PREFERENCE.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
LAMERS  
 

 
 
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