528  
FXUS10 KWNH 231904  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
303 PM EDT THU MAR 23 2017  
 
VALID MAR 23/1200 UTC THRU MAR 27/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
...PLEASE NOTE THAT THE NAM WAS UPGRADED TO A NEW VERSION 21/12Z  
CYCLE...  
 
12Z MODEL EVALUATION...INCLUDING FINAL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
   
..NORTHERN STREAM SHORTWAVE CROSSING SOUTH-CENTRAL CANADA TODAY
 
   
..CLOSED LOW DIVING THROUGH SOUTHEAST CANADA BY SAT MORNING
 
   
..COLD FRONT ADVANCING DOWN ACROSS THE GREAT LAKES/NORTHEAST
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
LARGEST DIFFERENCES DEVELOP ON SUN WITH THE MID-LEVEL TROUGH OVER  
SRN CANADA AND HOW THAT RELATES TO THE POSITION OF THE SURFACE  
BOUNDARY ACROSS THE NRN-MID ATLANTIC REGION. THE PRESENCE OF A  
STRONGER SHORTWAVE EMANATING FROM THE BRITISH COLUMBIA/ALBERTA  
BORDER THIS MORNING REACHING NEW ENGLAND SAT NIGHT ALLOWS FOR A  
DEEPER AND FARTHER SOUTH LOWER HEIGHTS ACROSS NRN NEW ENGLAND AND  
A FARTHER SOUTH SURFACE BOUNDARY IN THE 00Z ECMWF. THE 00Z ECMWF  
BACKED OFF OF THIS IDEA A BIT BUT REMAINS THE FARTHEST SOUTH WITH  
THE FRONT. MULTI-CYCLE TRENDS IN THE ENSEMBLES HAVE BEEN TO THE  
NORTH ALONG WITH THE DETERMINISTIC ECMWF...BUT THE ECMWF/ECMWF  
MEAN LAG THE LARGER CLUSTERING AND REMAIN SOUTH OF THE PACK. A  
FRONTAL POSITION NEAR THE 12Z GFS HAS MORE ENSEMBLE SUPPORT AND  
LIES NORTH OF THE ECMWF FOR SUN.  
 
   
..STRONG UPPER TROUGH CROSSING THE SOUTHWEST/FOUR CORNERS TODAY
 
   
..CLOSED LOW EVOLUTION OVER THE CENTRAL PLAINS FRI
 
   
..ENERGY CROSSING THE MID MS/OH VALLEYS THROUGH SAT
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 12Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY BELOW AVERAGE  
 
AT 500 MB...THERE HAS BEEN A NOTABLE TREND IN THE GEFS ENSEMBLES  
TO ADJUST FASTER COMPARED TO SLOWER EARLIER CYCLES...SO MUCH SO  
THAT THEY HAVE PASSED THE ECMWF ENSEMBLES WHICH HAVE BEEN TRENDING  
SLOWER VALID LATE FRI. WHILE DIFFERENCES ARE RELATIVELY MINOR  
THROUGH ABOUT 00Z/26...THE 12Z NAM/GFS PULL AWAY FASTER THAN THE  
12Z ECMWF/UKMET FOR SUN WITH THE 500 MB AND SURFACE COLD FRONT.  
THE 12Z CMC IS MORE SIMILAR TO THE NAM/GFS CAMP BUT IS DISPLACED  
NORTHWARD WITH THE MID-LEVEL LOW. THE INFLUENCE FROM AN UPSTREAM  
KICKER TROUGH MAY BE THE DECIDING FACTOR IN THE TIMING OF THE  
DOWNSTREAM FEATURE. GIVEN TRENDS IN THE GEFS BUT STEADY  
CONSISTENCY IN THE ECMWF...CONFIDENCE IS LOWERED. GOING IN THE  
MIDDLE IS THE BEST APPROACH AT THIS TIME...REPRESENTED BY A 50/50  
BLEND OF THE 12Z GFS AND 12Z ECMWF...WITH LITTLE ADJUSTMENT SEEN  
WITH THE 12Z ECMWF COMPARED TO ITS PREVIOUS CYCLE.  
 
...NORTHERN STREAM TROUGH/COLD FRONT REACHING THE NORTHWEST  
THURS/FRI...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL COMPROMISE  
CONFIDENCE: ABOVE AVERAGE  
 
THERE ARE ONLY MINOR TIMING DIFFERENCES WITH THIS SYSTEM AND ITS  
ASSOCIATED COLD FRONT...THUS A GENERAL MODEL COMPROMISE IS  
PREFERRED TO SMOOTH OUT THESE SMALLER SCALE DIFFERENCES.  
 
...SOUTHERN STREAM COMPONENT OF UPPER LEVEL TROUGH OVER THE WEST  
ON SAT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 12Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 12Z NAM/GFS HAVE TRENDED QUICKER WITH THE TIMING OF THE UPPER  
TROUGH MOVING THROUGH THE FOUR CORNERS REGION SAT EVENING...AND  
ARE FASTER THAN THE 00Z ECMWF/UKMET/CMC. HOWEVER...THE 12Z  
ECMWF/UKMET/CMC ADJUSTED FASTER AS WELL WITH LITTLE IMPACT TO THE  
TIMING OF THE TROUGH DESCRIBED IN THE SECOND SYSTEM DESCRIBED IN  
THIS DISCUSSION. TRENDS IN THE GEFS HAVE BEEN FASTER BUT THE ECMWF  
MEAN HAS BEEN INCONSISTENT. THE PREFERENCE IS TO GO WITH THE  
FASTER TRENDS LED BY THE 12Z MODEL SUITE.  
 
   
..UPPER TROUGH REACHING THE WEST COAST SUN EVENING
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z NAM/CMC BLEND  
CONFIDENCE: AVERAGE  
 
SPREAD HAS INCREASED REGARDING THE TIMING OF THIS SYSTEM TO REACH  
THE WEST COAST WITH THE 12Z UKMET ON THE FASTER SIDE OF THE LATEST  
GUIDANCE AND THE 12Z SHOWING A SLOWEST. AS HAS BEEN THE CASE WITH  
REPEATED UPPER TROUGHS IMPACTING THE WEST COAST FOR THE PAST WEEK  
OR SO...CONVERGENCE OF FASTER AND SLOWER CLUSTERS IN THE ENSEMBLES  
HAS TENDED TO GO TOWARD THE MIDDLE. THIS CONTINUES TO BE THE  
PREFERENCE...WITH THE MIDDLE BEST REPRESENTED BY THE 12Z NAM/CMC.  
 
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