I am finding the same thing also. My data is 2" soil temperatures. Here is some charts comparing a 3x3 ft cleared of residue(bare spot) and bent over rye stalks(rye residue). Most of the time it is like the charts for 5/1 but once in a while one like 5/7 shows up. In the case of 5/7 the air temps did not cool as much over night.

(harlans n o t 5 01 2014 full.bmp)

(harlans n o t 5 01 2014 par.bmp)

(harlans n o t 5 07 2014 full.bmp)

(harlans n o t 5 07 2014 par.bmp)

(harlans n o t 3x3 ft bare spot 5 03 2014.jpg)

(harlans n o t laid over rye 5 03 2014.jpg)

harlans n o t 5 01 2014 full.bmp (625KB - 65 downloads)

harlans n o t 5 01 2014 par.bmp (351KB - 59 downloads)

harlans n o t 5 07 2014 full.bmp (566KB - 69 downloads)

harlans n o t 5 07 2014 par.bmp (351KB - 51 downloads)

harlans n o t 3x3 ft bare spot 5 03 2014.jpg (121KB - 61 downloads)

harlans n o t laid over rye 5 03 2014.jpg (128KB - 62 downloads)