Sudden drop in my '05 Mileage

Up until three weeks ago, I was getting about 49mpg. Occassionally, I brushed past 50, but I never got the spectacular numbers some other members have. That's okay. I live at the edge of the Ozark uplift, and it's pretty darned hilly along my daily commuting route. Plus, the speed limit here is 70, which means my Prius spends a lot of the day in the 65-75 range.

Back in the first week of June, I set a new record, getting nearly 52MPG from a tank. I thought I had learned to control the car better, and that with warm weather coming on, I could see even better mileage. Instead, things took a turn for the worse. In the previous tank, mileage took a dive to 46.5. With 300 miles on the current tank, I'm running only 44.2.

However, before I go questing for a more elaborate excuse, there's one obvious answer: it's damn hot. The temp. here was 103 degrees yesterday, and the humidity near 80%. The last couple of weeks, 95+ temps and 80+ humidity has been the norm -- like living in a sauna. And I can definitely tell that the Prius AC is churning in an attempt to keep up.

What's the group experience? Can frequent (more like constant) AC use account for a 5-7MPG drop?

Thanks.

 

And now that I post this, I see other folks are also complaining about the heat eating into the all important numbers. I'd have noticed that before, if I wasn't so scorched by the heat.