My Response:

That kind of dramatic increase in the need for an extra 4-5 hours of sleep for 5 months of the year is not a common experience among meditators. 

There must be something else going on here. 

If you live in the mid to higher latitudes, it’s possible you may be suffering from Seasonal Affective Disorder. 

You may want to explore light therapies to see if they help.

Something else that might help is to make an effort to get more exercise during those months so that you go into a deeper sleep. 

That can make your sleeping hours more productive and rejuvenating, so that perhaps you can wake up refreshed after 7-8 hours. 

Try these ideas next winter. 

Otherwise, it might be an odd sleeping pattern that eventually wears out in a couple of more years.

Love,

Deepak