2019 Accord Hybrid - I usually get 43 around town, and if a lot of highway driving it drops to 36. No issue for me there. Car has 32k miles.
However after leaving the car at ouside airport parking for 2 weeks (Newark NJ) ,on the drive back to my house (about 50 miles) all highway - gas mileage dropped to 27.
Looking at the dash, I had a brief flash of something warning that had EV in the title, but it only lasted one second or less. No other issue or warning. Car drives normally,
Looking at the "power flow" screen it seems OK, but at one point the battery charge indicator went from about 8 bars immediately dropped to 2 bars. This was at constant speed. I am a bit frustrated trying to figure this out. Is there some cold weather phenomena for the hybrids?
Any suggestions are welcome.

 

I'd get the codes scanned since you had something flash on the cluster. A code can give you some direction on a possible issue with the hybrid battery/electric motor.

All batteries performance will drop in cold temperatures Like when the starter is slow when starting the engine on a very cold day. Hopefully a code will help. Pay attention to when the weather is warmer to see if the mpg increases.