Is lack of Canadian snow cover causing our mild fall?

It's been a mild October to remember, and an awesome fall for those who like it mild in Minnesota. Temperatures have been running about 7 degrees above average this month in the metro and much of southern Minnesota.

The official numbers will roll in Tuesday, but it appears this October will go down as one of the top 6 or 7 warmest on record for the Twin Cities, and possibly the 4th warmest on record for Minnesota.

The big question is, why?

One easy answer with weather patterns is always "random variability." Some years are just milder than others in fall and other seasons.

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But one answer may lie in the lack of Canadian snow cover ot the north this year.

Climatology would suggest that there should be snow cover all the way to the USA-Canada border by October 31st.

Snow cover "climatology" chart. Colored areas show where snow cover is usually present in late October.

(click image to enlarge!)

This year, as we open November Tuesday there is basically little or no snow cover to our north in much of central and southern Canada. You pretty much have to go al the way north to Great Slave Lake in the Northwest Territories to find continuous snow cover.

Snow cover as of Sunday. Note the lack of snow cover in much of Canada!

The relative lack of snow cover means that air masses over Canada are not chilled from below by the snow, and instead the ground is warmed by the sun. This "modifies" the air masses over Canada toward milder temps before they come south into Minnesota this year. The result is a lack of cold Canadian outbreaks this October.

It's pretty hard to get cold air to come south when highs have been in the 50s (with no snow on the ground!) in places like Edmonton and Calgary, Alberta.

The jet stream is also fairly far north for October this year, and that keeps us mild as well. It may be chicken and egg, but jet stream positions seem to also be influenced by snow cover patterns. It's possible that the jet has stayed north due to the relative lack of snow cover in Canada.

We'll be watching snow cover patterns to our north in the coming weeks. They may tell us a lot about when much colder air masses will finally start moving south into Minnesota.

PH