Over the past six months, temperatures in Kentucky have been all over the place. Everybody remembers that November and December were extremely cold, possibly the coldest November and December we've experience in the last 107 years, and certainly different from the previous three winters. As we moved into January, we experience more normal temperatures, but as we went into February the temperatures shot up and we experienced temperatures averaging five degrees above normal. Temperatures flip-flopped when we got into March, and we were nearly 5.4 degrees below normal. By the time we got into April, we had this tremendous explosion of heat and heat units increasing biological activity across the state, and we were 3.5 degrees above normal for April. For the whole time period we have been just slightly below normal. Tom Priddy interprets "Kentucky Monthly Rainfall Departures April 2000 -- April 2001"
Looking back over the last eight months in Kentucky, the rainfall departures out of those eight months we have had only two months (December of 2000 and February of 2001) where we had above normal rainfall. The other six months have been below normal rainfall for all of Kentucky. We came out of the drought season last fall really thinking we were in good shape, and we made it through the winter with two months of above normal rainfall and were lulled into thinking that we don't have to worry anymore. But that in fact was not the case because by the time we hit April, we had our 10th driest April and our fourth driest March and April since 1941, so we moved through that time on a downward spiral. Tom Priddy interprets "MRLS Degree Days Base 50 for 2001"
Probably the best way to look at how an explosive a growing season we had starting at the first week in March is to look at growing degree days, and we've coined "Growing Degree Days Base 50 MRLS." The first week in March we were considerably below normal on accumulating those heat units because March was a very cool month. But by the time we got into the second day of April, we had this explosion of temperatures such that we increased. The red line shows that we increased in one week 200 MRLS degree days in a one week period. And the next week even though we had some frost in the second week of April we continue to go above normal in an explosive manner such that by the end of April we'd accumulated a tremendous amount of heat units.
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."
Summary by Tom Priddy:
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.
Lexington, KY Weather Pattern (1980, 1981, and 2001)
Tom Priddy and Erin Maxwell of the UK Agricultural Weather Center reported the following on May 21: Over the years 1980, 1981 and 2001, there were below normal temperatures in March and above normal temperatures during April. In each year, the warm temperatures started during the end of March (1981) or first week in April (1980 and 2001). Also, frost/freeze conditions occurred on various dates in April for each year. During 1980, frost occurred on April 5th and 16th. For 1981, frost occurred on April 21, and during 2001, frost/freeze occurred on April 17 and 18. The temperatures for April 1981 and 2001 were the third and fourth warmest Aprils in the past 107 years. April 1980 was the 23rd coldest April in the past 107 years.