The last few days, I've been taking temperature readings of my garden, just before sunrise.

I thought I'd present some non-anecdotal evidence that yes, your beds are probably warmer than the air temperature. This morning, the air temp was 44 deg F (After a high of 67 yesterday) my beds (4' 2x6, full to around 5" with standard mel's mix, well watered) are holding steady at 55-56 deg.

Two 20 gallon bins of water nearby are 56 deg. These temps are the same as yesterday morning (47 deg air temp, 71 deg high the day before.)

Although the average ambient temperature (5 days of highs and lows from weather service) has been around 52, and lows have been in the range of 40-48, the beds (rather, probably the water stored in the vermiculite in them, warmed by the midday sun) does carry a considerable temperature buffer.

Penetrating the lawn nearby about 1 inch (as much as I could get into the packed ground) I measured 51 degrees today - my first time taking this measurement.

(Measured with a non-calibrated thermocouple on an Amprobe hand meter, not that it matters. :) )