I have the AWD system and when I travel on the interstate and it starts to rain, my mpg do drop. When the rain stops and pavement drys out, the mpg increases.

2005 AWD Escape Hybrid
Best Interstate tank trip MPG 39.02 (scangauge II) for 402 miles on I-70, 10.3 gallons used over mostly flat terrain. Aug. 2007

Best Interstate tank trip E30 MPG 34.6 for 271 miles along I-80 in Indiana and Ohio. May 2008

Best multiple road tank trip E30 MPG 36.2 for 202 miles in Southwestern Pa. July 2008.