This article, which includes information supplied by the National Oceanic and Atmospheric Administration, reports that the rise in temperatures in 2006 was due to the rising level of greenhouse gas emissions.
Greenhouse gas emissions responsible for increasing US temperatures: NOAA
...In 1998 when temperatures broke records, scientists attributed it to a powerful El Niño, which was changing the climate trends globally at that time.
However this time around, scientists said greenhouse gas emissions were the culprit. Furthermore the rise in emissions was associated with a 15-fold increase in the possibility of U.S. temperatures soaring above normal.
Checking over this article from the Energy Information Administration (Official Energy Statistics for the US Government) we find:
Coal production in the United States reached a record level in 2005, ending the year at 1,131.5 million short tons, according to data from the Energy Information Administration
...total U.S. coal consumption rose in 2005...
I have no idea if there is any correlation whatsoever, but I do know that if we continue to increase burning coal for energy, and the process of burning the coal continues to release greenhouse gasses of the same magnitude, we got even bigger trouble.