585  
FXUS10 KWNH 171613  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1112 AM EST SAT FEB 17 2018  
 
VALID FEB 17/1200 UTC THROUGH FEB 21/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
12Z GFS/NAM EVALUATION WITH PRELIMINARY MODEL PREFERENCES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
NAM/GFS INITIALIZATION ERRORS DO NOT SEEM TO DEGRADE THEIR SHORT  
RANGE FORECASTS.  
 
 
SHORTWAVE MOVING OFFSHORE THE NORTHWEST IN THREE DAYS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: MODEL BLEND; CONFIDENCE AVERAGE  
 
THERE IS A BIT OF DISPERSION IN POSSIBLE LOW PRESSURE PLACEMENT  
AND DEPTH ASSOCIATED WITH A SOUTHWARD MOVING SHORTWAVE MOVING DOWN  
THE WESTERN SIDE OF THE UPPER LEVEL TROUGH. OVER THE LAST SEVERAL  
DAYS, THE GUIDANCE HAS BEEN SLOWLY DAMPENING THIS FEATURE.  
CURRENTLY THE 12Z GFS IS A DEEP OUTLIER AND THE MULTI-DAY TREND  
SUGGESTS SOMETHING WEAKER BOTH ALOFT AND AT THE SURFACE. THE 00Z  
GLOBAL ENSEMBLE GUIDANCE HAS NO DEFINED SURFACE LOW TO TRACK IN  
THIS REGION, IMPLYING THAT A WEAKER SOLUTION WOULD BE BEST.  
BLENDING THE 12Z GFS WITH THE 12Z NAM, 00Z ECMWF, 00Z UKMET, AND  
00Z CANADIAN WILL ACCOMPLISH THIS TASK. CONFIDENCE IN THIS CHOICE  
IS NO BETTER THAN AVERAGE.  
 
 
UPPER TROUGH DIGGING INTO THE WEST  
PRESSURE PATTERN IN THE PLAINS/MIDWEST/GREAT LAKES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON UKMET-BLEND; CONFIDENCE AVERAGE  
 
BECAUSE THE 00Z UKMET HAS A SLIGHTLY SHARPER TROUGH ACROSS THE  
NORTHERN HIGH PLAINS AND WEST, ITS SURFACE LOW POSITION IN MI LATE  
TUESDAY IS MORE SOUTHWESTERLY THAN THE REMAINDER OF THE  
DETERMINISTIC GUIDANCE. WHILE THERE IS BROAD SPREAD IN THE  
POSSIBLE LOW POSITION, THE BEST CLUSTERING LIES NEAR THE 00Z  
CANADIAN, 00Z ECMWF, 12Z GFS, AND 12Z NAM. A BLEND OF THESE  
PIECES OF GUIDANCE IS PREFERRED WITH AVERAGE CONFIDENCE.  
 
LOW MOVING FROM THE SOUTHEAST OFFSHORE NEW ENGLAND  
AND ITS ASSOCIATED SHORTWAVE ALOFT  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: MODEL BLEND; CONFIDENCE SLIGHTLY ABOVE AVERAGE  
 
WHILE THE 12Z NAM IS STRONGER ALOFT AND A LITTLE MORE  
NORTHWESTERLY WITH THE SURFACE LOW TONIGHT, THIS TYPE OF SOLUTION  
HAS RANDOMLY SEEN OVER THE LAST SEVERAL DAYS ON VARIOUS PIECES OF  
GUIDANCE, LIES WITHIN THE ENSEMBLE CLUSTERING, AND CANNOT BE FULLY  
RULED OUT. BECAUSE OF THIS, A COMPROMISE OF THE 12Z GFS, 12Z NAM,  
00Z UKMET, 00Z CANADIAN, AND 00Z ECMWF IS PREFERRED WITH THIS  
SYSTEM WITH SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
ROTH  

 
 
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