865  
FXUS10 KWNH 021657  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1156 AM EST FRI FEB 02 2018  
 
VALID FEB 02/1200 UTC THRU FEB 06/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
   
..12Z NAM/GFS EVALUATION WITH PRELIMINARY PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE CROSSING THE PACIFIC NORTHWEST TODAY, TRACKING INTO  
THE ROCKIES ON SATURDAY AND REACHING THE MID-ATLANTIC COAST LATE  
SUNDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND  
CONFIDENCE: AVERAGE  
 
SOMEWHAT MINOR TIMING DIFFERENCES APPEAR WITH THIS FEATURE AFTER  
IT CROSSES THE ROCKIES AND REACHES THE LOWER MISSISSIPPI VALLEY.  
THE 12Z GFS IS A BIT FASTER THAN THE REMAINING DETERMINISTIC  
CONSENSUS, BUT THE BIGGER DIFFERENCE IS WITH A WEAK SURFACE LOW AS  
SEEN IN THE 12Z NAM. THE 12Z NAM IS NORTH OF THE  
DETERMINISTIC/ENSEMBLE CONSENSUS WITH THE SURFACE LOW NOTED  
12Z/04. ONLY MINOR DIFFERENCES EXIST OUTSIDE OF THE 12Z NAM UNTIL  
THE EAST COAST OF THE U.S. WHERE THE LATEST ENSEMBLE SCATTER LOW  
PLOTS BEST AGREE WITH THE 12Z GFS/00Z ECMWF.  
 
...SHORTWAVE TRACKING FROM WESTERN CANADA INTO THE NORTHERN PLAINS  
AND REACHING THE UPPER GREAT LAKES SUNDAY...  
...SURFACE LOW TRACKING ACROSS THE GREAT LAKES EARLY SUNDAY  
MORNING, REACHING SOUTHERN QUEBEC EARLY MONDAY MORNING WITH  
TRAILING COLD FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
PREFERENCE: 12Z NAM, 00Z ECMWF, 00Z UKMET BLEND THROUGH ~12Z/04  
12Z GFS/00Z ECMWF BLEND ~12Z/04 THROUGH 00Z/06  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
THE 12Z GFS IS FASTER WITH THE LEADING PORTION OF THIS ELONGATED  
UPPER WAVE, REACHING THE UPPER GREAT LAKES EARLIER THAN THE  
REMAINING MODEL CONSENSUS. A 12Z NAM, 00Z ECMWF, 00Z UKMET BLEND  
IS CLOSE TO THE ENSEMBLE MEAN PLACEMENT WITH A RELATED SURFACE LOW  
THROUGH ROUGHLY 12Z/04. BEYOND 12Z/04, A STRONGER SHORTWAVE BEGINS  
TO DOMINATE, APPROACHING THE OHIO VALLEY FROM THE NORTHWEST. THERE  
ARE ONLY MINOR TIMING DIFFERENCES WITH THIS NEXT WAVE, OUTSIDE OF  
THE FLATTER/WEAKER 00Z CMC. HOWEVER, GIVEN SOME INTERACTION WITH A  
SURFACE LOW ALONG THE MID-ATLANTIC COAST DISCUSSED IN THE PREVIOUS  
SECTION, A 12Z GFS/00Z ECMWF IS PREFERRED AS ONE SINGLE LOW BEGINS  
TO TAKE SHAPE AND STRENGTHEN NEAR MAINE. CONFIDENCE IS A BIT  
REDUCED GIVEN THE COMPLEX EVOLUTION OF THIS SYSTEM AND POOR  
ENSEMBLE AGREEMENT IN THE SCATTER LOW PLOTS.  
 
...ONSHORE FLOW INTO THE PACIFIC NORTHWEST WITH LOW AMPLITUDE  
SHORTWAVE MOVING INLAND SUNDAY NIGHT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-00Z CMC BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 00Z CMC IS OUT OF PHASE WITH THE SHORTWAVE NEAR THE NORTHWEST  
NOTED 00Z/05 AND OVERALL FLATTER DOWNSTREAM INTO THE INTERIOR  
WEST. OTHERWISE, DECENT MODEL AGREEMENT EXISTS WITH A NON-00Z CMC  
BLEND OF GUIDANCE.  
 
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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