Winter fuel consumption
Just about everyone's fuel economy is going to start dropping with the arrival of colder weather:
1) Higher rolling resistance (cold tires, bearings)
2) Are you keeping an eye on tire pressure? Tire pressure drops as outside temperature falls.
3) Engine oil, transmission oil/fluid gets thicker (unless they're 100% synthetic)
4) More accessory power draw (full lights, heater, defrost... which runs the A/C compressor as Dave points out, and running the A/C burns more fuel)
5) Idling??? Hopefully you're not idling your car to warm it up!! Use your Micra's block heater instead.
6) Engine takes longer to get up to normal operating temperature; spends proportionately more time running rich (and the automatic transmission holds lower gears longer until the engine warms up)
7) More aerodynamic drag (air density increases as temperature falls)
8) Are you running bare steel wheels with your snow tires? They will cause more aero drag than a wheel with a smooth wheel cover on it.
9) Winter gasoline formulation has slightly less energy density than summer gas.
10) Driving in snow: of course driving on actual snowy/slushy roads uses significantly more energy (even wet roads burn more fuel than dry roads).
It's not unusual to see a 10-20% drop in fuel economy in the middle of winter vs. summer.
You'll see a bigger drop in the winter if you mostly drive short city trips compared to someone who drives longer trips on the highway.
__________________________________________
View my fuel log 2015 Micra S manual: 5.0 L/100 km ... 56.5 mpg (Imp) ... 20.0 km/L ... 47.0 mpg (US) ...