Cold or hot temps put a drain on your mpg's - but having experienced my first winter in my Sonata Hybrid, I would say cold temps affect it more. A few little tricks can up your mpg's significantly. One thing I know to get optimal mpg's in any weather, you can't be showing any aggressive % in your driving style. I have friends who also own hybrids and can't figure out why they don't get great mpg's. Get a clue - the problem is with your right foot. Mine hovers between 65% - 80% eco, and 20% - 35% normal. I don't drive slow, keep up with traffic, and don't ever hold up traffic behind me, even if I'm the first in line at a light. I've learned to smoothly use the gas and brake pedals, anticipate coasting - let off the gas fully or partially if the light ahead just turned red or see brake lights, and start braking lightly for earlier, for longer distances, progressively adding pressure as I need to slow down more, to capture more regen. One trick I learned about in cold weather is to turn off the HVAC so the engine doesn't keep running to warm up, assuming you don't need the front defrost. Instead I use the heated seats and steering wheel when first starting on my trip, then when I reach a road where I will maintain speed for a bit, I'll turn the HVAC on. That allows the engine to stop when I'm coasting or not moving.
Side note: I haven't checked my Fuelly avg in quite some time, just keeping up with each fill-up entry on the mobile app on my phone, and just saw my avg is above 44! That was the goal I was shooting for months ago.