The History of National Weather Service Rain Gauges 

For the record, this civilian weather forecasting and data collection service has been in place since the late 1800s and was called the U.S. Weather Bureau until it was renamed the “National Weather Service” in 1970 – the same year I went off to college to study meteorology. To keep things simple, I’ll just call it by its current name – National Weather Service (NWS). We should define what we mean by “official”. Times may be changing here recently, but traditionally the word “official” was reserved for data collected by National Weather Service and selected fixed-point military weather stations equipped with approved standardized weather instruments. Official data was collected using standardized observational methods and recorded on standard federal weather observation data “forms” and archived by federal data repositories. Names of specific organizations have and continue to change over time, but currently, official weather data are archived and made accessible through NOAA’s National Centers for Environmental Information (NCEI).

Note before we get started: If anyone reading this document finds an error or lack of sufficient detail in the description that follow, and you feel you have more accurate and/or appropriately detailed information at your disposal, please don’t hesitate to contact me. I know a lot about precipitation measurements, and quite a lot about history, but I certainly don’t know or remember everything.

Our Starting Point

The U.S. Government Printing Office in 1888 published a remarkably detailed document on weather instrumentation and observations. It was entitled “Treatise on Meteorological Apparatus and Methods” and was authored by Professor Cleveland Abbe, Assistant in the office of the Chief Signal Officer Brigadier-General A. W. Greely. There are several hundred pages of text and figures. The very last section is on the measurement of precipitation – and is surprisingly brief, yet insightful. The chapter describes only one rain gauge and describes it in great detail. The gauge is simply called the “standard rain gauge”. I quote. “The diameter of the receiver is 8 inches, and the height of the instrument is 2 feet. The rim of the receiver is made of brass, beveled to a sharp edge and accurately circular. The brass rim is soldered to a galvanized iron funnel. The collecting tube is made of seamless brass tubing No. 16 of 2.53 inch inside diameter and 20 inches deep. With these dimensions the area of the measuring tube is to the nearest 1/100th of an inch one 10th the area of the receiving surface.” It goes on to say, “Each instrument is tested to determine the outstanding errors in the accuracy of the measuring tube and its ratio to the receiving surface, and corrections are furnished for any errors greater than ½ of 1% of the measured rainfall.” Even before the U.S. Weather Bureau was established in 1890, this was already the accepted standard. Other than some recent “upgrades” to a plastic funnel and clear plastic “receiving tube” and a stainless steel outer cylinder, the NWS standard rain gauge is still in use at several thousand stations that are still a part of the NWS Cooperative Network”. Our historic weather station here on the campus of Colorado State University still uses one of the oldies manufactured over 100 years ago. It was still in perfect shape until a groundskeeper crushed the side of the gauge two years ago with a riding lawn mower. It was reshaped in the machine shop and still works fine – but doesn’t look so good. Apparently, some of the early standard rain gauges used only a 6-inch outer cylinder holding the receiver (inner cylinder) and the 8” diameter funnel. But by the 1890's the 8” outer cylinder was “standard”. This was the only purely manual rain gauge ever sanctioned as “official” by the NWS until the scaled down 4” diameter gauge became available. Already by the late 1940's, federal weather observer manuals make mention of a 4” gauge – presumably metal in the early years. By the 1960's and possibly earlier, the plastic gauge essentially identical to what CoCoRaHS uses today was recognized by the NWS although lower in priority to other gauges. We’ll talk more about that momentarily.
 

Gauges used at First Order Weather Stations

By the late 1800s there was a network of dozens of professionally staffed weather stations in major cities across the country. This eventually grew to nearly 250 stations. Originally many of these were in or near urban centers. But the advent of civilian aviation resulted in many weather offices moving to airports. These stations eventually were tasked with taking detailed weather observations several times a day and in some cases round-the-clock. They were initially equipped with one or more standard rain gauges but soon began measuring precipitation more frequently. Two types of recording rain gauges were deployed beginning near the turn of last century. A precision tipping bucket rain gauge and a weighing type gauge. The tipping bucket was large with a 12” diameter collection funnel. Already by the year 1900, the tendency for tipping bucket gauges to under count rainfall from high intensity rain was well known. Because of this, the rainfall from the tipping buckets was then caught in a cylinder where it could be measured manually. The number of tips from the tipping mechanism could then be manually adjusted to the correct total.


When you have more than one gauge, which one do you use?

This question was addressed in several weather observing manuals. The policies as of January 1 of 1947 was whenever more than one type of rain gauge is in use at a station, the stick measurements made from the tipping bucket gauge will be regarded as the official measurements to which all other measurements will be corrected. If a tipping bucket gauge is not available, or if it is inoperative, the measurement from the 8-inch standard gauge will be regarded as the official measurement.

Two years later in 1949 additional details were offered as to gauge priority;
1) Wind shielded gauge of any type
2) Stick measurement of tipping bucket gauge
3) 8-inch gauge
4) 4-inch gauge
5) Weighing gauge

By 1961 the gauge priorities were changed again;
1) Weighing gauge equipped with 24-, 12- or six-hour gears
2) Stick measurement of tipping bucket gauge
3) 8-inch gauge
4) 4-inch gauge
5) All other types I have not found any confirmation, but I believe these gauge priorities were continued through the 1980s

Automation and the Modernized NWS

Beginning in the early 1990's, NWS Forecast offices were reorganized and weather observations were automated. A new generation of tipping bucket rain gauges was deployed as a part of the the Automated Surface Observing System (ASOS). It was designed to require little human contact and minimal maintenance. Unfortunately and quite frankly the early installations did not work very well and required several rounds of major“fixes”. It was replaced at many of stations by a more sophisticated weighing type gauge called the ”all-weather precipitation gauge” or AWPG. While a marked improvement over the initial ASOS HTB (heated tipping bucket) gauge, analyses are showing this gauge is also prone to under reporting precipitation, especially in cold climates.

Recording Rain Gauges in the NWS Cooperative Network

The national weather service cooperative network has relied mostly on manual gauges. However, motivated by the scientific and engineering data requirements and the financial support of the U.S. Army Corps of Engineers, recording rain gauges were also introduced into the cooperative observer network beginning in the late 1930s. Originally the 8-inch weighing bucket rain gauge was deployed which used a sensitive calibrated scale to weigh precipitation as it accumulated and ink on paper charts driven by spring-wound clocks to advance the paper to record the data. These carefully designed and manufactured gauges required weekly manual checks for changing paper, adding ink, winding clocks and, when necessary emptying the bucket. The processing of the “strip charts” also required considerable care to extract accurate data. These “universal weighing bucket gauges” were gradually replaced from the late 1960s into the 1990s by a heavy duty weighing gauge with a larger bucket requiring less manual intervention both on the data collection and the processing side. The replacement gauge was known as the Fischer-Porter recording gauge which used a punch tape mechanism to digitize data as it was collected. This gauge was eventually deployed at over 2000 locations across the country contributing data for NOAA's Hourly Data archive and publications. Only in very recent times (past 5-10 years) was this 1960s mechanical punch tape data recording mechanism updated to modern digital technology.
In summary, within the NWS Cooperative Network, only 4 styles of precipitation gauges have been used in the entire nearly 130 years of the network;
1) The 8” standard rain gauge
2) The 4-inch reduced-size version of the standard gauge
3) The universal weighing bucket rain gauge with ink on paper charts
4) The Fischer-Porter weighing gauge with data digitizing capabilities

If you have any questions, please do not hesitate to contact us by e-mail: info@cocorahs.org.