Standard daily pan evaporation is measured using the four-foot diameter Class A evaporation pan. The pan water level reading is adjusted when precipitation is measure to obtain the actual evaporation. Most Class A pans are installed aboveground, allowing effects such as radiation on the side walls and heat exchnges with the pan material. These effects tend to increase the evaporation totals. The amounts can then be adjusted by multiplying the totals b 0.70 or 0.80 to more closely estimate the evaporation from naturally existing urfaces such as a shallow lake, wet soil or other moist natural surfaces.

Many stations do not measure pan evaportation during winter months. A "0.00" total indicates no measuement is taken.

Stations marked with an asterisk * have estimated totals computed from meteorological measurements using a form of the Penman equation.

* = Less than 1/2 hour

Maximum 1-hour totals are based on data from top of the hour. Maximum 60-minute totals will be greater.

Only the first order stations record possible sunshine.

For more information click here on Western States, Alaska or Hawaii and Pacific Islands