I'm not no, 41m asl, I have a vantage vue 2m over grass, 70ft from my house and at least 120ft from any roads, I've often been suspicious of my low readings, I had one of -4.9c (well actually sustained low temps) on the 20th of November last year with that cold snap, but other stations reported similar low figures, under -4c. I currently have another 2 stations near me reporting minus figures
http://www.wunderground.com/personal-weather-station/dashboard?ID=IUNITEDK95
A year ago I also checked my low readings with another 2 digital stations, they were all within .1c of each other
Very odd!
edit: temps have been up and down tonight, hit -1.1c earlier, but it's less manic now, maybe there's somewhere nearby drying their hair in the garden