Ok, I will admit, I am a Southerner and I know you moms up North will laugh but...here goes.
I live in the South East USA and the weather has been horribly cold getting (to me) down to 20 at night. I grew up in sunny FL so I hate the cold. Since the most recent cold snap has started my milk seems to be fluctuating greatly. If I am inside my work home for an extended period of time then I can pump fine. If I go outside anytime a couple of hours before pumping I can barely get 1/3 the amount I normally get. It is not related to the time of day - just exposure to cold.
Any suggestions? If nothing else, I gave everyone a good laugh at my fear of cold weather! I bet my baby wears more clothing to protect her from the cold than most babies up north! Hee Hee.