Aug 5, 2011
Lower limit 55 F, upper limit 100 F
May 1 to August 1
Nicolaus
2009 1513
2010 1335
2011 1278
Durham
2009 1469
2010 1350
2011 1236
Colusa
2009 1600
2010 1413
2011 1344
To date 2011 is about 4-6 days behind 2010 and about 10-12 days behind 2009, depending the average number of degree units accumulated in one day used for the calculation.
Interestingly, the south valley is not cooler than the north valley using this measure. Any difference seems to be east to west.