I noticed in the last 2 months I have been getting less miles to the gallon, about 38-40. When I used to get 43-49 on my '06 Civic. I am not sure if it is the cold weather we have been having in New york or my driving. I know tire pressure and cold weather will hurt gas mileage. But a 5 mpg drop seems extreme. Last winter, I did not experience any decrease in gas mileage. (Although, the car was new.) Therefore, I have been getting only about 400 miles to a full tank. I have been average about 530 miles to a full tank. I commute in HOV lane 30 miles each way. I have about 19k miles on the car. I usually use 87 octane.

Has anyone seen decreases in mpg like this? Should I be worried? Is it the gas I use? Or I guess just hope for warm weather.