We examine the poleward transport of water vapor across 70°N during boreal winter in the ERA-Interim reanalysis product, focusing on intense moisture intrusion events. We analyze the large-scale circulation patterns associated with these intrusions and the impacts they have at the surface. A total of 298 events are identified between 1990 and 2010, an average of 14 per season, accounting for 28% of the total poleward transport of moisture across 70°N. They are concentrated over the main ocean basins at that latitude in the Labrador Sea, North Atlantic, Barents/Kara Sea, and Pacific. Composites of sea level pressure and potential temperature on the 2 potential vorticity unit surface during intrusions show a large-scale blocking pattern to the east of each basin, deflecting midlatitude cyclones and their associated moisture poleward. The interannual variability of intrusions is strongly correlated with variability in winter-mean surface downward longwave radiation and skin temperature averaged over the Arctic.