395  
FXUS10 KWNH 131845  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 PM EST TUE FEB 13 2018  
 
VALID FEB 13/1200 UTC THRU FEB 17/0000 UTC  
 
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
...CLOSED MID- AND UPPER-LOW INITIALLY OFF THE CA COAST MOVING  
INLAND...  
 
PREFERENCE: 13/12Z ECMWF AND 13/12Z NCEP BLEND...MOST HEAVILY  
WEIGHTED TO THE ECWMF.  
CONFIDENCE: AVERAGE  
 
THE 12Z NCEP MODELS TENDED TO HANDLE THE CLOSED LOW INITIALLY OFF  
THE CA COAST IN A SIMILAR FASHION IN THAT A SECONDARY VORT MAX  
ROTATING AROUND THE LOW HELPS PULL THE CENTER SOUTHWARD TO ABOUT  
32N. AS THE SECOND VORTICITY MAXIMUM CLOSES OFF AND FORMS A  
SECOND LOW SOUTH OF 20N...THE PRIMARY LOW LOSES ITS SOUTHWARD  
MOMENTUM AND BEGINS TO FILL AS IT EASES TOWARDS THE SOUTHERN CA  
COAST. THE 13/12Z ECMWF CONTINUED ITS EARLIER IDEA AND PULLED THE  
LOW OFF THE CA COAST SOUTHWARD IN RESPONSE TO THE SECONDARY  
VORTICITY MAXIMUM AND NEVER CLOSES A SECONDARY LOW OFF. THE RESULT  
WAS A SOLUTION WITH WEAKER VORTICITY MAXIMA IN THE SYSTEM. IN  
THAT RESPECT THE ECMWF MOVED CLOSER TO A MODEL CONSENSUS VALUE.  
HOWEVER, THE 13/12Z ECMWF STILL HAD MORE OF A CONNECTION WITH THE  
LINGERING SYSTEM OVER THE PACIFIC WHICH KEPT LOWER HEIGHTS THAN  
OTHER MODELS OVER FAR SOUTHERN CA.  
 
A SPAGHETTI PLOT OF 5700 METER HEIGHTS SHOWED REASONABLY GOOD  
OPERATIONAL AND ENSEMBLE AGREEMENT THROUGH 15/00Z...AT WHICH POINT  
THE DIFFERENCES OPEN. THE GFS HAD THE SUPPORT OF THE GEFS MEAN  
WHILE THE OPERATIONAL ECMWF HAD SUPPORT FROM THE ECMWF ENSEMBLES  
AND THE 13/00Z CANADIAN. THE 13/00Z UKMET STOOD OUT AS A  
WEAK/FAST OUTLIER BUT ITS 13/12Z RUN MOVED TOWARDS A STRONGER  
SOLUTION SIMILAR TO THE 13/00Z RUN OF THE ECMWF.  
 
AT THIS POINT...THINK THAT THE ECMWF AND UKMET MAY BE MORE CORRECT  
GIVEN THE MAGNITUDE OF UPSTREAM RIDGING ALONG 145W. BUT THE  
MAGNITUDE OF SHORTWAVE ENERGY DROPPING SOUTHWARD ALONG THE WEST  
COAST BECOMES A PLAYER ON DAY 3. THINK THAT TEMPERING THE 13/12Z  
ECMWF/UKMET WITH SOME NAEFS OR GEFS WILL MITIGATE SOME OF THE  
UNCERTAINTY ON DAY 3.  
 
   
..SHORTWAVE ENERGY INITIALLY OVER THE NORTHEAST PACIFIC OCEAN
 
 
PREFERENCE: 13/12Z GEFS/NAEFS...  
CONFIDENCE: AVERAGE  
 
THE MODELS HAVE A SIMILAR IDEA THAT SHORTWAVE ENERGY INITIALLY  
OVER THE NORTHEAST PACIFIC AND THE GULF OF ALASKA WILL DROP  
SOUTHEAST ON THE PERIPHERY OF A BROAD UPPER RIDGE. THE 13/00Z  
ECMWF WAS PARTICULARLY STRONG WITH THIS WAVE...ESPECIALLY BY THE  
TIME IT REACHES THE BASE OF THE MEAN TROUGH OVER CALIFORNIA.  
WHILE THE 13/12Z UKMET MOVED TOWARDS THE STRONGER WAVE DROPPING  
SOUTHEAST...THE 13/12Z ECMWF WENT WITH A WEAKER SOLUTION THAT WAS  
CLOSER TO A MODEL COMPROMISE.  
 
AS A RESULT, WILL RECOMMEND THE 13/12Z ECMWF/UKMET TEMPERED A BIT  
BY THE LATEST GEFS MEAN/NAEFS. THINKING IS THAT DOING SO WILL  
KEEP THE TIMING OF THE ECMWF/UKMET WHILE REDUCING THE AMPLITUDE OF  
THE WAVE SOMEWHAT.  
 
...SHORTWAVES FROM THE GREAT BASIN TOWARDS THE GREAT LAKES AND  
NORTHEAST U.S....  
 
PREFERENCE: 13/12Z GFS/UKMET/ECMWF BLEND  
CONFIDENCE: BELOW AVERAGE  
 
THE MODELS SHOW A PAIR OF 700-500 MB SHORTWAVES IN THE NORTHERN  
STREAM, WITH THE FIRST WAVE STARTING IN THE NORTHERN PLAINS  
TONIGHT AND MOVING INTO THE UPPER MS VALLEY TUE AS IT  
DEAMPLIFIES. THE WAVES THEN BECOMES HARDER TO TRACK AS THEY  
WEAKEN WHILE THEY APPROACHING THE UPPER GREAT LAKES.  
 
ON WED, A NEW WAVE EJECTS FROM THE NORTHERN PLAINS AND MOVES EAST  
NORTHEAST ACROSS THE UPPER MS VALLEY AND LAKES,THEN INTO THE LOWER  
LAKES AND NORTHEAST THU. THE PRIMARY DIFFERENCES APPEAR TO BE  
RELATED TO TIMING.  
 
DUE TO BETTER AGREEMENT AMONGST THEMSELVES, PREFER THE 13/12Z  
GFS/UKMET/ECMWF. THE PROBLEM IS THAT THESE FEATURES ARE WEAK AND  
PRONE TO FAIRLY LARGE RUN TO RUN MODEL DIFFERENCES. THIS LIMITS  
OUR CONFIDENCE IN THE MODEL SELECTION.  
 
BANN  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 

 
 
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