Fore Cast

Weather for the Turf Industry

About Growing Degree Day (GDD) Maps

Degree days are a means by which turf and weed development can be monitored.


The maps show the accumulation of base 50°F growing degree days (GDD) for three accumulation intervals:

  1. Last week is the number of that accumulated over the last 7 days.
  2. Next week is a forecast based on National Weather Service forecast guidance for GDD accumulation over the next seven days.
  3. A seasonal accumulation is given for the period from March 1 until the current day.

Base 32°F growing degree day accumulation is an experimental measure for predicting ideal annual bluegrass seedhead development and potential assessment with plant growth regulators. Preliminary data suggests that the ideal application time might be from 400-600 GDD for proxy and 500 to 650 GDD for embark.

In terms of days, the GDD comparisons are able to answer the question, "When during the last (or average) growing season did the current GDD accumulation occur?" A mapped value of -7 indicates that the current season is a week behind the last year's (or the average) accumulation. If 50 GDD had accumulated on April 7, 2006, a mapped value of -7 would indicate that in 2005 there was already 50 GDD accumulated on April 1, 2005.


The other type of comparison is in terms of GDD. If 50 GDD had accumulated April 7, 2006, while in 2005 75 GDD had already accumulated, the mapped value would be -25.