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The below graphs dealing with the Oroville Dam, the Oroville Dam Spillway Weather Station, and the Thermalito River Outlet Weather Station were obtained from the CDEC. The orange box added to both temperature graphs highlights those degrees which are below the lower threshold temperature for these mites. The light blue box indicates the lower threshold temperature for plumeria (estimated from damage seen in the greenhouse for temperatures below 40 degrees Fahrenheit). Both of these were added as overlays and are not part of the original graphs.
The above graph represents the weather conditions present for the property in the foothills which is located at the same elevation as the dam and slightly south of it. Note the difference between low temperatures for the foothills and valley and represents the "banana belt effect" whereby cold mountain air seeps into the valley at night which forces the warmer air from the day up into the foothills.
The above graph represents the weather conditions present for the valley.
Note the number of days where the maximum relative humidity was greater than 80%. Although I am not certain as to the exact level where egg hatching for the mites decreases, observations from the mite tent which has high relative humidity levels (~92% on 01-30-12) indicates that at those levels mite populations are restrained, and the plants can better defend themselves as a result.
Again note the number of days where the maximum relative humidity level was above 80%. Since this weather station is located adjacent to the river outlet and afterbay, the below graph is provided for comparison and represents data obtained from the weather station located at the Oroville airport, a few miles from the river and outlet.
So far this has been a fairly dry year.