From AER blog:
Siberian snow cover got off to a quick start in September and that has continued into October (see Figure ii), however it seems to me the rapid advance of late September has slowed a bit in October. In fact in a bit f an unusual twist the surface temperatures have been more impressive this month (as in cold) than the snow cover, typically it is the reversed. Above normal Siberian snow cover extent (SCE) favors a weak polar vortex this winter and more widespread severe winter weather across the NH. But the persistence of the pattern that is supportive of a rapid advance of Siberian snow cover for remainder of the month remains cloudy and uncertain in my opinion. As I thought might happen and mentioned in the last blog, the trough across Siberia transitions to high-pressure ridging, this scenario is now predicted by the models. That would greatly reduce the odds of a weak polar vortex and colder weather this winter. This seems to have been a fairly common occurrence the past few Octobers. If there is a sign that the cavalry is coming (that is if you are a winter weather enthusiast) it is the development and even dominance of Greenland blocking. That should squash any Siberian ridging and resume the rapid advance of Siberian SCE. But predicting high latitude blocking is a known model weakness and confidence for the second half of October is low