To get access to all of the CIMIS data and features, register as a user.
  The link to register is at the upper right-hand corner of the CIMIS web page.

Network Maintenance

The Department of Water Resources (DWR) operates the CIMIS weather station network to collect and disseminate high quality, accurate, and reliable irrigation scheduling data to the public. To meet this objective, DWR is standardizing the operations and maintenance of the network. All the weather stations in the CIMIS network are virtually identical, in that they all have the same equipment and sensors and operate similarly. All station equipment and sensors are mounted on a mast, pole, or tripod base. The sensors and their heights are as follows:
Picture of weather station with all of the sensors defined

Sensor   Sensor Height

Pyranometer (solar radiation), Wind Vane, and Anemometer (wind speed)   2 meters
Air Temperature & Humidity Sensor   1.5 meters
Rain Gauge   1 meters
Soil Temperature   15 cm underground


A small datalogger mounted on the mast of each station is connected to the electronic sensors by wires. Once every minute, the datalogger takes a reading of each sensor and records it. It continues for one hour, then averages the 60 readings for an hourly average, or accumulates the 60 readings for an hourly total, and stores all these in its memory. It continues collecting data in this manner throughout the day (midnight to midnight). After 24 hours have elapsed, the datalogger then calculates the daily averages and totals using the 24 hourly averages and totals and stores them. The datalogger also determines the maximum and minimum temperatures and relative humidities. These values are the highest and lowest of the one-minute readings during the day.

After 12:00 midnight (Pacific Standard Time) the main CIMIS computer begins requesting data from the stations (polling). This communication is done by telephone or internet. Each station has its own telephone service and modem. Polling data continues through the early morning hours and is finished for most stations by 4:00 a.m. Some stations will not answer the phone call from the main computer during these early morning hours due to phone connection problems.

Polling continues for these stations and is usually retrieved by 9:00 or 10:00 a.m. The polling process repeats itself every 4 hours throughout the day to provide updated hourly data.

After receiving the data, the CIMIS computer then performs three tasks:
1) Reference Evapotranspiration (ETo) is calculated,
2) The data is run through the quality control program and flags are placed appropriately
3) The data is stored in a database for retrieval by CIMIS users.

Once CIMIS weather station data has entered the database, it can be accessed by Spatial CIMIS and combined with satellite data to provide Spatial CIMIS ETo. See the Spatial Overview tab for more details.


Maintenance standards call for a CIMIS weather station maintenance visit every 3-4 weeks during the warmer months of the year. Visits decrease to about every five or six weeks in the cooler months.

DWR maintained stations are visited by DWR staff out of DWR's Regional Offices. Many other CIMIS stations are cooperatively maintained with help from local agencies or individual people. All DWR maintained CIMIS weather stations are maintained according to standards developed by DWR, including twice a year sensor calibration against a set of standardized calibration sensors. Although our CIMIS stations not maintained or owned by DWR are of high quality, DWR has limited control over the accuracy or reliability of the weather data from them.

During the maintenance visit the station sensors are checked for operation and accuracy and cleaned or replaced as required. Grass (fetch) in the field around and under each station is mowed regularly to a height of about three inches. The grass is irrigated and fertilized to keep it actively growing.

If you have any questions about station locations, siting environment, CIMIS data, or possible cooperation for a new weather station, please call CIMIS Staff from one of our four DWR Regional Offices.