Degree Days (DD)

Our preliminary research has indicated that the emergence of adult mosquitos (Culex) typically occurs after the accumulation of 230 base 50°F daily degree days. In order to estimate emergence in a given year, maps showing the accumulation of degree days during the last week and since March 15 are provided.

For longer range planning, a map of the average date on which 230 degree days accumulate is given. The range of dates on which this degree day threshold has been historically reached is illustrated by the 10% and 90% probability maps. There is a 10% chance of accumulating 230 degree days before the indicated dates on the 10% probability map. Similarly in 90% of the years 230 degree days can be expected before the dates on the 90% probability map.