099  
FXUS10 KWNH 201903  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
203 PM EST TUE FEB 20 2018  
 
VALID FEB 20/1200 UTC THRU FEB 24/0000 UTC  
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
   
..12Z MODEL EVALUATION WITH FINAL PREFERENCES
 
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
 
***NOTE THAT DUE TO DATA FLOW ISSUES AT WPC/NCWCP, THE 12Z  
ECMWF/UKMET/CMC WERE NOT AVAILABLE FOR COMPARISON AND THE  
PRELIMINARY DISCUSSION BELOW WILL SERVE AS THE LAST DISCUSSION FOR  
THIS DATA CYCLE***  
 
...POSITIVELY TILTED MID-UPPER LEVEL TROUGH OVER THE WESTERN U.S.  
WITH STRONG COLD FRONT PASSING THROUGH THE NORTHEAST ON  
WEDNESDAY...EXTENDING SOUTHWESTWARD INTO THE SOUTHERN PLAINS...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: 12Z GFS / 00Z ECMWF BLEND  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE 12Z GFS WAS NOTED TO BE SLIGHTLY QUICKER WITH THE PROGRESSION  
OF THE LEADING EDGE OF THE MID-UPPER LEVEL TROUGH INTO A POTENT  
RIDGE SITUATED IN THE WESTERN ATLANTIC, WHEN COMPARED TO THE  
REMAINING MODEL GUIDANCE. THIS IS NOTED EARLY ON THURSDAY FROM THE  
NORTHERN MID-ATLANTIC INTO THE LOWER MS VALLEY. ENSEMBLE MEANS  
SUPPORT THEIR RESPECTIVE DETERMINISTIC RUNS WITH A BLEND OF THE  
FASTER GFS AND SLOWER ECMWF APPEARING REASONABLE AT THIS TIME. AT  
THE SURFACE, THE 12Z NAM LOOKS TO TAKE A WEAK SURFACE LOW ALONG  
THE MS VALLEY TOO FAR NORTH AND WEST WHEN COMPARED TO THE  
REMAINING CONSENSUS.  
 
...SHORTWAVE AMPLIFYING SOUTHWARD ALONG THE WEST COAST ON  
THURSDAY...POSSIBLY CLOSING OFF IN THE MID-LEVELS BEFORE REACHING  
THE FOUR CORNERS REGION ON FRIDAY...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: GENERAL MODEL BLEND  
CONFIDENCE: AVERAGE  
 
THERE ARE RELATIVELY MINOR DIFFERENCES WITH THIS WAVE...THE 12Z  
NAM SHOWS STRONGER/MORE CLOSED OFF WITH THE SHORTWAVE, THE 12Z GFS  
IS SLIGHTLY FASTER AND THE 00Z ECMWF LESS AMPLIFIED AND SLOWER.  
THE 00Z UKMET/CMC SEEM TO SPLIT THESE DIFFERENCES WITH VARYING  
DEGREES OF SPREAD DEPENDING ON THE FORECAST HOUR NOTED THROUGH  
00Z/24. OVERALL, A GENERAL MODEL BLEND IS PREFERRED AS NO SINGLE  
MODEL APPEARS TO BE BEST AT ALL FORECAST HOURS, WITH A BLEND  
APPEARING TO SMOOTH OUT THE DIFFERENCES AND RESULT IN A SOLUTION  
NEAREST TO THE ENSEMBLE MEANS.  
 
...LOWER AMPLITUDE SHORTWAVE NEARING THE PACIFIC NORTHWEST ON  
FRIDAY WITH ASSOCIATED COLD FRONT...  
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
PREFERENCE: NON-00Z ECMWF BLEND  
CONFIDENCE: BELOW AVERAGE  
 
THE 00Z ECMWF IS FLATTER AND FASTER WITH THIS SHORTWAVE AS IT  
APPROACHES THE PACIFIC NORTHWEST, WHILE A NON-00Z ECMWF CONSENSUS  
SUPPORTS CLOSER TO THE MORE AMPLIFIED 12Z NAM/GFS. GIVEN THE  
AMPLIFIED NATURE TO THE UPPER FLOW OVER THE CENTRAL AND EASTERN  
PACIFIC OCEAN, MORE AMPLIFICATION DOWNSTREAM OF A BUILDING RIDGE  
OVER ALASKA BY FRIDAY MAKES SENSE. HOWEVER, CONFIDENCE IS BELOW  
AVERAGE GIVEN LARGER THAN AVERAGE ENSEMBLE SPREAD WITH NO CLEAR  
TREND AND A WIDE RANGE OF POSSIBILITIES SEEN IN THE ENSEMBLE  
SPAGHETTI DATA.  
 
MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
500 MB FORECASTS AT WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 
OTTO  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page