Knowing the soil temperature is critical for judging if this is really the right time to plant! It is very easily to put seeds into soil that is colder than idea. We use a cooking thermometer like this normally used to stick into meat!
Nothing fancy, but try not to misplace it. Push the stem into the soil, I like to measure at ~2 inches.
Here is a nice table from the Soil Temperature Guide (G2122) from the University of Nebraska for the recommended minimum temperatures needed for germination:
One time, the soil 1.5 to 2 inches deep was running 32~35 degrees F but a week later the dark soil was reading 50 degrees F. It depends on the sun (and a bit on the lack of rain and wind).
Ideally, our seeds sprout just ahead of the weed seeds.
Another source of similar information.