505  
FXUS10 KWNH 021843  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
143 PM 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 MODEL EVALUATION WITH FINAL PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
...SHORTWAVE CROSSING THE PACIFIC NORTHWEST TODAY, TRACKING INTO  
THE ROCKIES ON SATURDAY AND REACHING THE MID-ATLANTIC COAST LATE  
SUNDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 12Z ECMWF / 12Z CMC 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. THE 12Z UKMET STRENGTHENS THIS LOW AS IT TRACKS NORTH  
TOWARD NEW ENGLAND, WITH THIS LOW BECOMING DOMINANT, NORTH OF THE  
WEAKER NAM/GFS/ECMWF/CMC LOWS SEEN BY 12Z/05. THE LATEST ENSEMBLE  
SCATTER LOW PLOTS BEST AGREE WITH THE 12Z GFS/ECMWF/CMC BLEND FOR  
THIS LOW.  
 
...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: NON 12Z GFS BLEND THROUGH ~12Z/04  
12Z GFS/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. WHILE THE 12Z CMC IS THE NEXT FASTEST  
MODEL, A NON-12Z GFS 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 SLOWER/WEAKER 12Z CMC. WORTH NOTING HOWEVER, THE  
12Z NAM IS ON THE STRONGER SIDE OF THE GUIDANCE, NOTED AT 850 MB  
WITH THE LOW AND EXTENT OF COLDER TEMPERATURES, SO THE NAM IS  
CONSIDERED A LOW PROBABILITY POSSIBILITY. GIVEN SOME INTERACTION  
WITH A SURFACE LOW ALONG THE MID-ATLANTIC COAST DISCUSSED IN THE  
PREVIOUS SECTION, A 12Z GFS/12Z ECMWF IS PREFERRED AS ONE SINGLE  
LOW BEGINS TO TAKE SHAPE AND STRENGTHEN NEAR MAINE BEYOND 12Z  
SUNDAY. 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: GENERAL MODEL 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.  
 
THE 12Z CMC ADJUSTED TOWARD THE REMAINING DETERMINISTIC CONSENSUS  
WITH ONLY MINOR ADJUSTMENTS NOTED IN THE 12Z UKMET/ECMWF RELATIVE  
TO THEIR PREVIOUS CYCLES.  
 
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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