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U.S Record Short-term Rainfalls
As a follow up to my last blog I thought I would write up a short summary of the most intense short-term rainfalls in U.S. records.
This spring has seen some phenomenal heavy rain events (as outlined in my previous blog). Some of these included very intense short-term precipitation totals such as the 1.02” in 30 minutes at Kansas City Airport on May 27 and 0.69” in 3 minutes at Houston’s Hobby Airport on April 27th. How do these stack up compared to the all-time U.S. records for such?
Below is a table of the most intense rainfalls on record over various periods of time:
One-minute rainfalls
It is hard to imagine how an accurate measurement of precipitation over a 60-second period can be made. However, the U.S. Weather Bureau conducted several exhaustive studies of the Unionville, Maryland claim to 1.23” in one minute on July 4, 1956 and determined it to be accurate (see for the Monthly Weather Review summary). A recording rain gauge: A Friez Universal Type with a 12-inch capacity, dual traverse pen, and 24-hour clock gear on a chart drum was used to make the measurement. It had good exposure and measured a storm total of 3.60” between 2:50 p.m and 11:30 p.m. with 2.84” of this falling in a 50-minute period between 2:50-3:40 p.m. The minute that ostensibly measured the 1.23” total occurred around 3:22-3:23 p.m. Here is a copy of the trace:
Although invisible in this reproduction, there is apparently a faint line on the original trace which is when the excessive rainfall occurred. From ‘Monthly Weather Review’, August 1959 p. 304.
A number of experiments were made on the gauge to determine its calibration and accuracy. The gauge passed all the tests to which it was subjected. Anecdotal information also played a part in the record’s certification. Extreme flash flooding and erosion were reported in the surrounding area and the sky became so dark that residents were forced to turn lights on in spite of being mid-afternoon. Roof gutters were overwhelmed, with water reported flowing off roofs “like Niagara Falls”.
The Unionville figure is generally considered not only the U.S. record for one minute but also the world record for such. A much-quoted 1.50” at Barot, Guadeloupe o November 26, 1970 cannot be verified (in fact, there appears to be no such location on the Caribbean island).
Other significant one-minute rainfalls include 0.69” at Jefferson, Iowa on July 10, 1955 and 0.65” at Opid’s Camp, California on April 5, 1926. At Jefferson 1.00” fell in 109 seconds.
Other amazing short duration rainfalls
The officially recognized U.S. rainfall for a 5 minute period was the 2.03” reported at Alamogordo Creek, New Mexico on June 5, 1960 (3.09” fell in 15 minutes). Fort McPherson, Nebraska reported 1.50” in 5 minutes on May 27, 1868 as did Pensacola, Florida on May 2, 1937. Patterson, New Jersey measured 1.64” in 8 minutes on July 13, 1880. Tyler, Texas reported 2.00” in 10 minutes on April 29, 1905. The validity of the above measurements is open to question.
What is the greatest one-hour rainfall in the U.S.?
This is a matter of debate. There appear to be no ‘official’ records for such since each of the proposed cases has its own flaws. The most commonly cited figure is 12.00” at Kilauea Plantation, Kauai, Hawaii on January 24, 1956. This was part of a state record 24-hour rainfall that totaled at Least 38.00” on January 24-25 that year. However, the observer noted that the gauge was overflowing at several times during his observation cycle so the actual figures may have been considerably higher. A severe thunderstorm at Catskill, New York was reported to have dropped at least 10” of rain in one hour on July 16, 1819 according to bucket surveys. The most intriguing candidate, however, is for a location (unidentified with a specific town) in central West Virginia on the night of August 4-5, 1943. A U.S. Army Corps of Engineers storm report claims that 13.80” of rain fell in one hour between 11:30 p.m and 12:30 a.m. the night of August 4-5. This was measured by a remote gauge simply named No. 86. It appears to have been located near the town of MacFarlon (which measured 5” in 1 hour) in Ritchie County. Another gauge identified as No. 48 picked up 15.0” of rain in about one and a half hours.
The isohyetal map for the storm of August 4-5, 1943 in West Virginia that may have dropped 13.8 in one hour. Page from ‘Storm Studies’, Dept. of the Army, Corps of Engineers.
Another fascinating rainstorm, and perhaps of the greatest intensity on record for anywhere in the world, is the famous Smethport, Pennsylvania event of July 18, 1942. During this event an amazing 34.50” of rain reportedly fell (according to several bucket surveys) in a 12-hour period between midnight August 17th and noon August 18th. Of this, 28.50” fell in 3 hours (9.a.m-noon) and 30.70” in 6 hours. Mountainsides were reported to have their vegetation stripped to bedrock and 11 people drowned in the valley around the town. Other precipitation measurements made in the area included 20.4” in 12 hours at Emporium, PA and 18.5” at Mt. Jewett. An official USWB gauge in Salamanca, New York received 6.7” in 3 hours.
The isohyetal map for the storm of July 17-18, 1942 in Pennsylvania and New York that may have dropped 28.5” in three hours, a world record. Page from ‘Storm Studies’, Dept. of the Army, Corps of Engineers.
You may find it curios that so many of these records seemed to have happened in the 1940s and 1950s. This is not a coincidence. During the 1940s and 1950s the U.S. Government (via the Army Corps of Engineers) was very interested in determining what the maximum possible rainfall rates for any given location might be in order to engineer the massive infrastructure improvements that were being made across the country those decades.
The map above is an approximation of what the absolute maximum amount of rainfall that could possibly fall in a 24-hour period across the U.S. east of the Rockies might be, according to research by the Army Corps of Engineers. The actual measured maximum amounts by state are indicated by the blue dots. These are not official figures but 24-hour precipitation amounts that the USACE observed while investigating their ‘Storm Rainfall’ reports which resulted in a massive 1000-page plus compendium of intense short-duration rainfall observations. Map reproduced form ‘Extreme Weather: A Guide and Record Book’, based upon Army Corps of Engineers data.
Christopher C. Burt
Weather Historian
As a follow up to my last blog I thought I would write up a short summary of the most intense short-term rainfalls in U.S. records.
This spring has seen some phenomenal heavy rain events (as outlined in my previous blog). Some of these included very intense short-term precipitation totals such as the 1.02” in 30 minutes at Kansas City Airport on May 27 and 0.69” in 3 minutes at Houston’s Hobby Airport on April 27th. How do these stack up compared to the all-time U.S. records for such?
Below is a table of the most intense rainfalls on record over various periods of time:
One-minute rainfalls
It is hard to imagine how an accurate measurement of precipitation over a 60-second period can be made. However, the U.S. Weather Bureau conducted several exhaustive studies of the Unionville, Maryland claim to 1.23” in one minute on July 4, 1956 and determined it to be accurate (see for the Monthly Weather Review summary). A recording rain gauge: A Friez Universal Type with a 12-inch capacity, dual traverse pen, and 24-hour clock gear on a chart drum was used to make the measurement. It had good exposure and measured a storm total of 3.60” between 2:50 p.m and 11:30 p.m. with 2.84” of this falling in a 50-minute period between 2:50-3:40 p.m. The minute that ostensibly measured the 1.23” total occurred around 3:22-3:23 p.m. Here is a copy of the trace:
Although invisible in this reproduction, there is apparently a faint line on the original trace which is when the excessive rainfall occurred. From ‘Monthly Weather Review’, August 1959 p. 304.
A number of experiments were made on the gauge to determine its calibration and accuracy. The gauge passed all the tests to which it was subjected. Anecdotal information also played a part in the record’s certification. Extreme flash flooding and erosion were reported in the surrounding area and the sky became so dark that residents were forced to turn lights on in spite of being mid-afternoon. Roof gutters were overwhelmed, with water reported flowing off roofs “like Niagara Falls”.
The Unionville figure is generally considered not only the U.S. record for one minute but also the world record for such. A much-quoted 1.50” at Barot, Guadeloupe o November 26, 1970 cannot be verified (in fact, there appears to be no such location on the Caribbean island).
Other significant one-minute rainfalls include 0.69” at Jefferson, Iowa on July 10, 1955 and 0.65” at Opid’s Camp, California on April 5, 1926. At Jefferson 1.00” fell in 109 seconds.
Other amazing short duration rainfalls
The officially recognized U.S. rainfall for a 5 minute period was the 2.03” reported at Alamogordo Creek, New Mexico on June 5, 1960 (3.09” fell in 15 minutes). Fort McPherson, Nebraska reported 1.50” in 5 minutes on May 27, 1868 as did Pensacola, Florida on May 2, 1937. Patterson, New Jersey measured 1.64” in 8 minutes on July 13, 1880. Tyler, Texas reported 2.00” in 10 minutes on April 29, 1905. The validity of the above measurements is open to question.
What is the greatest one-hour rainfall in the U.S.?
This is a matter of debate. There appear to be no ‘official’ records for such since each of the proposed cases has its own flaws. The most commonly cited figure is 12.00” at Kilauea Plantation, Kauai, Hawaii on January 24, 1956. This was part of a state record 24-hour rainfall that totaled at Least 38.00” on January 24-25 that year. However, the observer noted that the gauge was overflowing at several times during his observation cycle so the actual figures may have been considerably higher. A severe thunderstorm at Catskill, New York was reported to have dropped at least 10” of rain in one hour on July 16, 1819 according to bucket surveys. The most intriguing candidate, however, is for a location (unidentified with a specific town) in central West Virginia on the night of August 4-5, 1943. A U.S. Army Corps of Engineers storm report claims that 13.80” of rain fell in one hour between 11:30 p.m and 12:30 a.m. the night of August 4-5. This was measured by a remote gauge simply named No. 86. It appears to have been located near the town of MacFarlon (which measured 5” in 1 hour) in Ritchie County. Another gauge identified as No. 48 picked up 15.0” of rain in about one and a half hours.
The isohyetal map for the storm of August 4-5, 1943 in West Virginia that may have dropped 13.8 in one hour. Page from ‘Storm Studies’, Dept. of the Army, Corps of Engineers.
Another fascinating rainstorm, and perhaps of the greatest intensity on record for anywhere in the world, is the famous Smethport, Pennsylvania event of July 18, 1942. During this event an amazing 34.50” of rain reportedly fell (according to several bucket surveys) in a 12-hour period between midnight August 17th and noon August 18th. Of this, 28.50” fell in 3 hours (9.a.m-noon) and 30.70” in 6 hours. Mountainsides were reported to have their vegetation stripped to bedrock and 11 people drowned in the valley around the town. Other precipitation measurements made in the area included 20.4” in 12 hours at Emporium, PA and 18.5” at Mt. Jewett. An official USWB gauge in Salamanca, New York received 6.7” in 3 hours.
The isohyetal map for the storm of July 17-18, 1942 in Pennsylvania and New York that may have dropped 28.5” in three hours, a world record. Page from ‘Storm Studies’, Dept. of the Army, Corps of Engineers.
You may find it curios that so many of these records seemed to have happened in the 1940s and 1950s. This is not a coincidence. During the 1940s and 1950s the U.S. Government (via the Army Corps of Engineers) was very interested in determining what the maximum possible rainfall rates for any given location might be in order to engineer the massive infrastructure improvements that were being made across the country those decades.
The map above is an approximation of what the absolute maximum amount of rainfall that could possibly fall in a 24-hour period across the U.S. east of the Rockies might be, according to research by the Army Corps of Engineers. The actual measured maximum amounts by state are indicated by the blue dots. These are not official figures but 24-hour precipitation amounts that the USACE observed while investigating their ‘Storm Rainfall’ reports which resulted in a massive 1000-page plus compendium of intense short-duration rainfall observations. Map reproduced form ‘Extreme Weather: A Guide and Record Book’, based upon Army Corps of Engineers data.
Christopher C. Burt
Weather Historian
Extreme Weather Precipitation Records
The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.