important. With only five years of data, however, individual synoptic events with
a time scale of a few days sometimes dominate the unfiltered record.
A running average of the mean daily temperature for all five sites for the
annual cycle is shown in Figure 3, along with a graphical depiction of our sea-
sonal nomenclature. Figure 4 shows monthly mean temperatures for the sites.
Figure 5 shows running averages of daily maximum and minimum temperatures
and diurnal temperature ranges by season. The rationale for the season names
becomes apparent when considering the location of the freezing isotherm in the
daily minimum temperature plot.
The Warm Season (WS) corresponds closely with that period of the year
when diurnal mean temperatures are consistently above freezing (Fig. 5) and
active plant growth occurs. At most sites the warmest temperatures of the year
occur in early to mid-July, just a few weeks after the summer solstice, when daily
Figure 3. Eleven-day running average of the mean daily tem-
perature for the five sites over the annual cycle. The axis label
corresponds to the first day of that month. Also graphically
depicted are the seasonal definitions for Warm Season (WS),
Early Cold (EC), Deep Cold (DC), and Late Cold (LC).