305  
FXUS10 KWNH 221827  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
127 PM EST THU FEB 22 2018  
 
VALID FEB 22/1200 UTC THRU FEB 26/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z MODEL EVALUATION...WITH LATEST MODEL PREFERENCES AND CONFIDENCE  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
   
..FRONT STRETCHING FROM THE MID-ATLANTIC TO SOUTHEAST TEXAS
 
   
..SURFACE WAVE CROSSING THE UPPER MS VALLEY/GREAT LAKES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: ABOVE AVERAGE  
 
THE MODELS ARE IN REASONABLY GOOD AGREEMENT WITH THE ORIENTATION  
OF THE SURFACE FRONT ACROSS THE SOUTH THIS PERIOD, AND ALSO WITH  
THE DETAILS OF THE SURFACE WAVE LIFTING UP ACROSS UPPER  
MISSISSIPPI VALLEY AND GREAT LAKES. A GENERAL MODEL BLEND WILL BE  
PREFERRED.  
 
   
..SHORTWAVE INITIALLY OVER THE PACIFIC NORTHWEST
 
   
..DROPPING INTO THE FOUR CORNERS REGION ON FRIDAY
 
   
..CYCLOGENESIS OVER THE PLAINS AND LIFTING TO THE MIDWEST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS TAKE RATHER STRONG SHORTWAVE TROUGH DIGGING DOWN ACROSS  
THE PACIFIC NORTHWEST AND DROP IT QUICKLY INTO THE FOUR CORNERS  
REGION ON FRIDAY. MODEL SPREAD IS MINIMAL UNTIL THE SYSTEM EJECTS  
OUT INTO THE PLAINS BY SATURDAY WHERE WELL-DEFINED CYCLOGENESIS  
WILL OCCUR AND THE SYSTEM LIFTS NORTHEAST TOWARD THE MIDWEST. THE  
12Z NAM ENDS UP STRONGER ALOFT WITH ITS ENERGY TRAVERSING THE  
UPPER MIDWEST. THE 12Z GFS IS ALSO QUITE ENERGETIC, ESPECIALLY  
WITH ITS DEGREE OF NEGATIVE TILT AND STRONG VORT ENERGY, BUT DOES  
NOT HAVE QUITE THE DEGREE OF HEIGHT FALLS AS THE NAM. THE 12Z  
UKMET, 12Z CMC AND 12Z ECMWF ALL SHOW A SOMEWHAT WEAKER SYSTEM.  
HOWEVER, THERE IS SOME DEGREE OF ENSEMBLE SUPPORT FROM THE GEFS  
AND THE ECENS FOR A SOMEWHAT STRONGER LOW CENTER TO EVOLVE WITH A  
NEGATIVELY TILTED TROUGH THAT LIFTS NORTHEAST OUT OF THE CENTRAL  
PLAINS AND ACROSS THE UPPER MIDWEST. ADDITIONALLY, THERE WAS SOME  
TREND COLLECTIVELY FROM THE CMC, UKMET AND ECMWF TOWARD A SOMEWHAT  
STRONGER SOLUTION, BUT STILL NOT TO THE EXTENT OF THE NAM ALOFT,  
OR THE GFS AT THE SURFACE. FOR NOW, WILL SUGGEST A COMPROMISE IN  
MASS FIELDS FROM THE GFS AND ECMWF WHICH MAKES FOR A MODEL CLUSTER  
MORE CLOSELY REPRESENTING THE MODEL CONSENSUS AT THIS TIME.  
 
   
..SHORTWAVE ARRIVING OVER THE PACIFIC NORTHWEST ON SATURDAY
 
   
..CROSSING THE FOUR CORNERS/HIGH PLAINS ON SUNDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-GFS CONSENSUS  
CONFIDENCE: AVERAGE  
 
THE NEXT IN A SERIES OF SHORTWAVES TO DROP SOUTHEAST DOWN ACROSS  
WESTERN NORTH AMERICA AND INTO THE PACIFIC NORTHWEST WILL ARRIVE  
ON SATURDAY AND THEN RAPIDLY DROP DOWN INTO THE FOUR CORNERS  
REGION ON SUNDAY. THE MODELS ARE IN GOOD AGREEMENT WITH THE MASS  
FIELD DETAILS OF THIS SYSTEM UNTIL SUNDAY WHEN THE 12Z UKMET  
BEGINS TO LAG THE MODEL CONSENSUS, AND THE 12Z GFS BEGINS TO  
OUTRUN IT. THE 12Z CMC AND 12Z ECMWF TEND TO FAVOR THE SLOWER  
UKMET, WITH THE 12Z NAM MORE IN BETWEEN THE GFS AND NAM. THERE IS  
A BIT BETTER ENSEMBLE SUPPORT FOR THE SLOWER CONSENSUS INCLUDING  
THE GEFS MEAN AND ECENS MEAN AS THE ENERGY BEGINS TO EJECT OUT  
INTO THE SOUTHERN HIGH PLAINS BY LATE SUNDAY. WILL PREFER THE  
SLOWER CONSENSUS AWAY FROM THE GFS FOR NOW, LED BY THE NON-NCEP  
GUIDANCE.  
 
   
..SHORTWAVE ARRIVING OVER THE PACIFIC NORTHWEST ON SUNDAY
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: BLEND OF THE 12Z GFS AND 12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE GUIDANCE BRINGS ANOTHER SHORTWAVE INTO THE PACIFIC NORTHWEST  
ON SUNDAY ALONG WITH A PROGRESSIVE COLD FRONT. THE GUIDANCE IS IN  
RELATIVELY GOOD AGREEMENT ALTHOUGH THE 12Z NAM APPEARS TO BE  
PERHAPS JUST A TAD MORE PROGRESSIVE. A BLEND OF THE 12Z GFS AND  
12Z ECMWF BEST APPROXIMATES THE MODEL CONSENSUS AT THIS TIME, AND  
SO A BLEND OF THESE SOLUTIONS WILL BE PREFERRED FOR NOW.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ORRISON  
 

 
 
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