466  
FXUS10 KWNH 131655  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1154 AM 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: 13/00Z ECMWF AND 13/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 13/00Z ECMWF ALSO PULLED THE LOW OFF THE CA COAST  
SOUTHWARD IN RESPONSE TO THE SECONDARY VORTICITY MAXIMUM...BUT THE  
EC NEVER CLOSES A SECONDARY LOW OFF. AS A RESULT, THE 13/00Z  
ECMWF HAS A STRONGER VORTICITY MAXIMUM REACHING THE SOUTHERN CA  
AROUND 15/00Z THAN DOES THE GFS/NAM...AND KEEPS THE VORTICITY  
CENTER AS A MORE COHERENT ENTITY INTO COLORADO THAN DOES THE NCEP  
RUNS.  
 
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.  
 
AT THIS POINT...THINK THAT THE ECMWF 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. GIVEN THAT THE ECMWF WAS STRONGER WITH THIS  
ENERGY THAN OTHER MODELS, THINK THAT BLENDING IN SOME OF THE  
GFS/GEFS AND THE NAEFS MAY TEMPER SOME OF THE UNCERTAINTY AT THIS  
POINT ESPECIALLY ON DAY 3.  
 
   
..SHORTWAVE ENERGY INITIALLY OVER THE NORTHEAST PACIFIC OCEAN
 
 
PREFERENCE: 00Z 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.  
FIRST REACTION WAS THAT THE ECMWF WAS TOO STRONG, BUT FORECASTERS  
IN THE WPC MEDIUM RANGE SECTION POINTED OUT A SIMILAR EVOLUTION  
RECENTLY WHICH VERIFIED ON THE STRONGER SIDE OF THE GUIDANCE.  
 
AS A RESULT, WILL RECOMMEND THE 13/00Z ECMWF TEMPERED A BIT BY THE  
13/00Z GEFS MEAN/NAEFS. THINKING IS THAT DOING SO WILL KEEP THE  
TIMING OF THE ECMWF 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 AND 13/00Z 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  
AND 13/00Z UKMET/ECMWF. THE PROBLEM IS THAT THESE FEATURES ARE  
WEAK AND PRONE TO FAIRLY LARGE RUN TO RUN 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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page