Standard-type rain gages are visited weekly or at no more than one month intervals. Storage gages have higher capacity and might be visited as few as two times per year, after and before the rainy season (spring and fall). The longest running standard gage is at the Climatic Station at WS2. Totals from this gage were used to adjust both the daily and high resolution precipitation records recorded by the Universal recording gage (1957-2013) and now the Noah IV recording gage (2013-present). Similarly, standard gages at Hi-15 (1963) and Mack Creek (1979) have run alongside recording gages since their original installation. All of the standard and storage gages have been paired with the highest correlating recording gage to build daily records.
The 8-inch non-recording standard rain gage (SRG) is an open mouth can with straight sides with 20-inch capacity and is the National Weather System standard. While there is a collector funnel and measuring tube in the traditional gage, the outer overflow can is used as the primary means of collection to better capture frequent snow events. Originally turbine oil and now food-grade mineral oil (150 ml) is added to the SRG to prevent evaporation and RV antifreeze (.5-1 liter) is added in winter to prevent freezing. The can is weighed and compared with a tare weight to determine millimeters of precipitation. The SRGs have typically been placed in small clearings without an alter shield. The Belfort Universal recording rain and snow gauge has an 8" orifice diameter and 12-inch capacity with accuracy of 0.3%.
The locally crafted SRG is made from 2' sections of schedule 26 PVC pipe, wall thickness of 5/16". The bottom is capped and the top edge beveled to prevent rain from splashing in. The average inside diameter is 7 7/8". These have 30" holding capacity. Water from these gages is weighed and converted to millimeters.
The Sacramento Storage Gage has an 8" orifice diameter with approximately 200 inches storage capacity and is mounted on platforms. Water depth is measured with tapes and calibrated to inches through individual rating tables for each gage. The Sacramento storage gage consists of a 15-gal oil drum and a sheet metal cone assembly. The oil drum serves as the storage can. The cone assembly has three parts. The cone and inner skirt are cut from 24-gage and the catch ring from 22-gage galvanized sheet metal. The top of the catch ring is beveled from the outside to form a cutting edge. The inner skirt prevents loss of precipitation between the cone and can. The complete gage is mounted on a tower to keep the top of the gage well above maximum snow depth.
The stand-alone rain gage is composed of 10-inch standing pipe w/tank gage, a propane-heated 20-inch diameter orifice and surrounded by a Valdai-style double wind fence. A temperature probe controls orifice heating by turning on/off a pump and heater. The capacity is about 28 inches.
The shelter-top design requires a shelter for the storage wells and other equipment with the orifice mounted on the roof of the shelter with alter wind shield. The orifice is heated by directing the heat from a propane heater to the orifice via duct pipe and turned on/off based on a controlling temperature sensor. The storage well depth is measured to determine precipitation.
The prorating process builds daily data from periodic precipitation totals of the non-recording standard or storage rain gages (SRG). Once precipitation is determined through a field check of the SRG for each measurement period, totals from the paired recording rain gage are determined for the same intervals. A ratio between the standard (or storage) gage (SRG) and the recording gage is determined. The daily record from the recording gage is multiplied by its ratio to the SRG to estimate the daily precipitation for the SRG. If the total SRG precipitation total is flagged in any way (e.g., estimated, questionable, missing), this flag is applied to each day within the SRG collection interval. Should a significant portion of the recording gage record be missing for a given interval, an alternate recording gage will be used to "prorate" the SRG record into daily values. The paired recording gage used to prorate the SRG total is recorded and listed for each date.
The paired recording gage for each SRG was originally determined through regression analysis of corresponding precipitation totals of the SRG versus each of three recording gages. The three recording gages used were gages operational in 1994: CS2MET, H15MET and GSMACK. These three are still used for the remaining five SRG (standard or storage gages), and CENMET is used as an alternate should there be missing data for any of these.