From 1895 to 1998 the Contiguous USA warmed at a very small rate of .78F per century. The NOAA graph is here.
The interesting thing is that 34% of the warming occurred in the month of February. January even had a slight cooling trend.
From 1998 to 2013, the USA cooled at a rate of -3.33F per century. February was responsible for 66% of the cooling.
Any ideas? Is it an NOAA artifact or something else? It seems strange that CO2 would prefer February for 100 years and then forsake it. 🙂
Graphs for each month/period below. (The percentages do not add up properly because some months were going in opposite direction of overall trend, but they give an idea of the magnitude)
Click for bigger.
sunshine hours 
Did you mean to say “February was responsible for 66% of the WARMING”?.
No. The USA has cooled since 1998.
Feel free to check: http://www.ncdc.noaa.gov/cag/time-series/us/110/00/tmp/ytd/11/1998-2013?trend=true&trend_base=100&firsttrendyear=1998&lasttrendyear=2013
There number is slightly different than mine because I use monthly data up to Nov 2013 and their graph can either show annual (no 2013 data) or Year To Date.
K. I guess I don’t get it. Maybe it’ll come to me yet. … I’ll stare at it some more. 🙂