885  
FXUS10 KWNH 171835  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
135 PM 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 MODEL PREFERENCES WITH CONFIDENCE INTERVALS  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
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 SLIGHTLY ABOVE AVERAGE  
 
DISPERSION IS NARROWING WITH 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, THOUGH  
SOME OF THE 12Z GUIDANCE BECAME A LITTLE STRONGER. THE 00Z GLOBAL  
ENSEMBLE GUIDANCE HAS NO DEFINED SURFACE LOW TO TRACK IN THIS  
REGION, NORMALLY IMPLYING THAT A WEAKER SOLUTION WOULD BE BEST.  
THE NOTICEABLE STRENGTHENING SEEN IN THE UKMET/CANADIAN GUIDANCE  
LOWERS CONSIDERATION OF THE 00Z GLOBAL ENSEMBLE GUIDANCE TO SOME  
DEGREE. BLENDING THE 12Z GFS, 12Z NAM, 12Z ECMWF, 12Z UKMET, AND  
12Z CANADIAN ACCOUNTS FOR THE UNCERTAINTY AND IS PREFERRED WITH  
SLIGHTLY ABOVE AVERAGE CONFIDENCE.  
 
 
UPPER TROUGH DIGGING INTO THE WEST  
PRESSURE PATTERN IN THE PLAINS/MIDWEST/GREAT LAKES  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: MODEL BLEND; CONFIDENCE SLIGHTLY ABOVE AVERAGE  
 
THE 12Z UKMET CAME IN LOOKING CLOSER TO THE OTHER AVAILABLE  
GUIDANCE, CLOSE ENOUGH TO BE CONSIDERED PLAUSIBLE. A BLEND OF THE  
12Z CANADIAN, 12Z NAM, 12Z GFS, 12Z UKMET, AND 12Z ECMWF IS  
PREFERRED WITH SLIGHTLY ABOVE 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,  
12Z UKMET, 12Z CANADIAN, AND 12Z 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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