2009 is the fourth coldest summer on record in Ann Arbor, but is this cold weather happening everywhere?

One of the services that agricultural weather data sites put together is a "growing degree day map", which shows how hot a season has been overall. Growing degree days measure how much hotter a day is than a baseline (in the below map, 50 degrees); the map below shows the difference between the normal for the season and this year.

At a glance the conclusion is that Michigan and much of the upper midwest has had a relatively cold year, but that Texas has been hot and the southeast has been relatively warm.

For more maps and other information there is a lot of detail at the Integrated Plant Protection Center of Oregon State University. Their notes say that hese maps are calculated daily using the GIS GRASS 5.4, and are based on 1) near-real time temperature data from 12,000+ AgriMet, HydroMet, National Weather Service, RAWS, Snotel, and weather stations from dozens of other networks, 2) historical average temperature data (1971-2000 Normals) from the National Climate Date Center (clim84), 3) PRISM monthly max and min temperature maps, and 4) corrections based on inverse-distance squared interpolations of differences between PRISM map-based and real-time degree-day calculations.