479  
FXUS10 KWNH 121945  
PMDHMD  
 
MODEL DIAGNOSTIC DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
245 PM EST MON FEB 12 2018  
 
VALID FEB 12/1200 UTC THRU FEB 16/0000 UTC  
 
 
...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR  
INGEST...  
 
PLEASE REFER TO THE WPC QPFPFD PRECIPITATION FORECAST DISCUSSION  
FOR DETAILS ON MODEL PREFERENCES AND SYSTEM TIMING UNTIL THE NEXT  
PMDHMD IS ISSUED AT 1645 UTC.  
 
...MID-UPPER LEVEL LOW AND 700 MB TROUGH DRIFTING ACROSS CA INTO  
THE ADJACENT SOUTHWEST US...  
 
PREFERENCE: BLEND OF 12Z UKMET, 12Z NAM, 00Z/12Z ECMWF  
CONFIDENCE: AVERAGE  
 
THE MODELS ARE IN GOOD AGREEMENT IS SHOWING A CLOSED LOW NEAR THE  
CA/NV BORDER TONIGHT THAT DRIFTS SOUTHWEST ACROSS CA INTO THE  
EASTERN PACIFIC NEAR THE CA COAST, AND THEN TURN SOUTHEAST ALONG  
THE CA COAST.  
DIFFERENCES IN THE MODEL MASS FIELDS MOSTLY EMERGE ON WEDNESDAY,  
WITH THE GFS FORECASTING THE ORIGINAL CENTER TO MOVE FURTHER  
OFFSHORE AND A NEW CENTER TO FORM WITHIN THE 700 MB TROUGH AS IT  
MOVES ACROSS SOUTHERN CA.  
THE GFS WINDS UP WITH A SLIGHTLY MORE AMPLIFIED WAVE THAN THE  
OTHER MODELS.  
ONE ASPECT OF THE GFS THAT IMPROVED FROM THE 00Z RUN WAS IT SLOWED  
DOWN THE 700 MB TROUGH TIMING TO BE IN BETTER  
AGREEMENT WITH THE NAM, 00-12Z ECMWF, AND UKMET.  
 
THE PREFERENCE IS TO USE THE MAJORITY CLUSTER OF THE  
NAM/UKMET/00-12Z ECMWF DUE TO EXCELLENT AGREEMENT.  
   
..SHORTWAVES EJECTING ACROSS THE NORTHERN TIER OF STATES
 
 
PREFERENCE: BLEND OF 00Z/12Z ECMWF, 12Z GFS  
CONFIDENCE: AVERAGE  
 
THE MODELS SHOW A PAIR OF 700-500 MB WAVE 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 AND BECOMES  
HARDER TO TRACK AS IT WEAKENS 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. THE 12Z  
NAM APPEARS TO BE THE FASTEST, WHILE  
THERE IN BETTER AGREEMENT AMONG THE GFS, UKMET, AND 00Z ECMWF.  
THIS GROUP OF 3 MODELS ALSO DEAMPLIFIES THE WAVE ON THU.  
DUE TO BETTER AGREEMENT, THE MAJORITY CLUSTER OF THE GFS/UKMET/00Z  
ECMWF IS PREFERRED. THE 12Z ECWMF HAS TRENDED SLOWER, AND IS ON  
THE SLOW EDGE OF THE GUIDANCE DISTRIBUTION.  
 
...WAVE CROSSING THE PACIFIC NORTHWEST/NORTHERN ROCKIES WED AND  
INTO THE NORTHERN PLAINS TO CENTRAL GREAT BASIN AND SOUTHERN CA  
THU...  
 
PREFERENCE: BLEND OF 00Z/12Z ECMWF, 12Z UKMET  
CONFIDENCE: SLIGHTLY ABOVE AVERAGE  
 
THE MODELS ARE IN BETTER THAN AVERAGE AGREEMENT IN SHOWING A 500  
MB WAVE CROSSING VANCOUVER ISLAND TUE NIGHT AND THEN THE PACIFIC  
NORTHWEST AND NORTHERN ROCKIES WED, FOLLOWED BY THE NORTHERN AND  
CENTRAL GREAT BASIN AND THEN SOUTH ACROSS CA.  
THE GFS AND NAM AREA FEW HOURS FAST WITH A SLIGHTLY LESS  
AMPLIFIED TROUGH CROSSING WY AND CO. THE 00-12Z ECMWF, UKMET AND  
09Z SREF MEAN ALL SHOW SLOWER TIMING. USUALLY IN A PATTERN WITH AN  
AMPLIFIED UPSTREAM RIDGE (MODELS FORECASTING A CLOSED EASTERN  
PACIFIC HIGH BY 00Z FRI)THE SLOWER SOLUTION PAN OUT BETTER, SO THE  
SLOWER ECMWF/UKMET/SREF MEAN ARE PREFERRED.  
 
PETERSEN  
 
PREVIOUS MODEL TRENDS AT WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML  
PREVIOUS 500 MB FORECASTS AT  
WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML  
 

 
 
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