Tom Priddy, a meteorologist at the University of Kentucky's College of Agriculture, put together data on the weather this spring that is thought to have caused the current equine problems associated with pasture.
Charts and audio clips are available online at http://www.uky.edu/Agriculture/VetScience/mrls/weatherdata
"A degree day is really a dimensionless number that we use to relate growth of corn, for example, or growth of insects. We use it also for heating degree days and cooling degree days. Basically what we do is take the day's maxi-min temperature, divide that by two, come up with the average temperature, and subtract some base from it. For the purposes of this study, the MRLS degree days, we used base 50. That may be changed at some point in time. For alfalfa weevils, for example, we use a base of 48. So we accumulate those daily differences over time and we can compare that to not only last year or last week, but we can also compare it to normal. And what this is showing is the explosive nature of the increase of heat units that occurred starting that first week in April this year. That implies that we had this explosion of biological activity in the state of Kentucky.
"In summary, this start of the growing season was a certainly a rare event. We had this huge temperature increase as we moved through April, where we had an extremely cool March, but there was an explosive type of heat units accumulation. This was superimposed over the stress of a major drought experienced in 1999. At the same time we had major frost freeze that caused damage across the state on the 17 and 18th of April, and again on the 25th with a renewal of the explosive types of temperature degree day accumulations even after that and that is way this was a very rare year."