Is it possible to calculate the evaporation rate using the data collected using a Kestrel 4500? If this were possible/advisable, is there a formula you could give us to calculate the evaporation rate when the data were post-processed?

This question is usually asked when a user wants to get wind direction with the same meter they are getting evaporation, the 4500 is currently the only model that takes direction.

Yes, it is possible to determine the evaporation rate using the Kestrel 4500 (even easier with the post-processing method you propose).  The ACI (American Concrete Institute) has listed the formula (one in SI and one in imperial units) on this page:

I would probably perform this calculation during post-processing.  However, you’ll also need to log the surface temperature of the concrete (done with an independent probe such as a laser thermometer) and use that value in the formula on the page above.