From their accompanying disco:
'The ECMWF  ensemble mean amplifies an upper-level 
trough over the Southwest, which results  in an increase in 
500-hPa heights across the Southeast and a warming trend  after below normal temperatures on days 6 and 7."
"
Since there are signs that the  period of below normal temperatures may be short-lived, a two class change in  the temperature outlook from yesterday was necessary for parts of the eastern  
CONUS. The Madden-Julian 
Oscillation (MJO) recently strengthened, with its  enhanced phase shifting east across the West Pacific. Lagged composites from  this center of enhanced convection would tend to favor persistence of below  normal temperatures across the central and eastern U.S. through Week-2. Since  this 
MJO influence on the temperature pattern differs from the ECMWF model  trend, forecast confidence is low in the temperatures outlook east of the  Rockies. Below normal temperatures are most likely across the western Gulf  Coast and lower Mississippi Valley due to an amplifying 
trough aloft. Increased  chances of above normal temperatures across the Great Lakes and Northeast are  consistent with the positive 
500-hPa height 
anomalies over Canada, while  Pacific flow favors above normal temperatures along the West Coast."
"The official 8-14 day 
500-hPa height 
blend consists of: 
40% of Today's 6z GFS  Ensemble Mean centered on Day 11, and 60% of Today's 0z European Ensemble Mean  centered on Day 11"
Note below how warm is the day 11 0Z Euro (12Z Euro similar)! The models, especially Euro ens, have warmed considerably since yesterday morning:
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