Michigan State University's oft-used growing degree-day map series has been updated to make the model even more user friendly for professional turf managers and others.
The GDD maps provide real-time seasonal accumulated degree-day (base 50) totals across Michigan as well as departures from normal in terms of GDDs and calendar days. The new map has improved color contrast and clearer numbers to make it easier to read. More than the appearance has changed, however. The source of the data used to produce the maps also is different. The data behind the new GDD surfaces are obtained from a new data product series from NOAA National Weather Service called UnRestricted Mesoscale Analysis. URMA is a collection of gridded weather datasets developed using a combination of numerical model output and available observations, which includes some Enviro-weather station data) The spatial resolution of the data is approximately 1.5 miles, which can provide highly detailed, contoured maps of weather variables and derived variables, such as GDDs, across a region of interest.
Although the gridded data values are not quite as precise as the individual station observed data, they can provide a good estimate of conditions in a given area, especially when there are missing observations or sites.
In addition to GDD accumulation maps, this Enviro-weather application provides maps that compare the current degree-day accumulation to the climatological "normal." There are two comparisons that can be accessed by clicking on "Current degree-day maps" on an Enviro-weather station page, and scrolling down the page. The first map shows current GDD totals in comparison to normal in terms of number of calendar days ahead or behind.
For example, if the current observed GDD total at a given location is 50 units greater than the climate normal and the normal accumulation at that point in the season is 10 GDDs per day, the map will indicate that the GDD totals are 50/10 or five days ahead of normal. The second (bottom) map shows current GDD totals in comparison to normal in terms of GDD units. Both give users a feel for the progress of the growing season compared to what has been observed in the past.
The new 2016 version incorporates slightly different data for determining what is "normal." To calculate "normals" in the old version of this product, climatic data from 1981 to 2007 was used. The new 2016 version utilizes data from 1981-2010, which is the current international standard 30-year period for climatic normals.
Because the daily GDD normals were calculated with station data from about 90 individual sites within and near the state, which is everything that was available at the time they were developed, the spatial normal GDD patterns may in some cases be less detailed over space than is the case with the new URMA data. As a result, users might see some relatively larger departures from normal that appear to be related to geographical features. In Michigan, this issue is most common in lakeshore areas where air temperatures and GDD totals may vary significantly over only short distances, especially during the spring season when the relatively cool lakes slow accumulation of GDDs. Enviro-weather is working to resolve this issue and any differences are expected to be relatively small.