Some hybrid owners use an engine block heater to speed up or ensure optium fuel efficiency. I hate to think what mileage you would obtain in real winter conditions that some of us experience three or so months a year.

2005 AWD Escape Hybrid
Best tank trip MPG 39.02 (scangauge II) for 402 miles on I-70, 10.3 gallons used over mostly flat terrain.

Best tank trip MPG 34.6 for E30 for 271 miles along I-80 in Indiana and Ohio.