"Blocking" is the result of a high pressure system persisting over an area for several days leading to a stagnation of weather patterns (see this description for more detail).
Affects of Blocking (Barnes et al. 2014)
Blocking is strongly tied to weather extremes in the midlatitudes (e.g., cold snaps, heat waves) and can persist for days to weeks [e.g., Black et al., 2004; Dole et al., 2011], so an increase in blocking could mean an increase in weather extremes as Arctic sea ice continues to decline. However, both observational and modeling studies suggest that any potential link between sea ice and midlatitude weather may be masked by internal variability [e.g., Barnes, 2013; Screen et al., 2013]