BOISE HEAVIEST RAIN EVENTS (>= 1.00 INCH in 24 HOURS) 1. 2.24 6/11,12/1958 c- 21. 1.21 6/14,15/1907 w 2. 2.05 5/28,29/1990 22. 1.20 4/30,5/1/1938 c 3. 1.74 9/11,12/1976* 23. 1.19 9/12,13/1939 w+ 1.74 8/5-8/2009& w- 1.19 4/19,20/1981 w- 4. 1.65 3/20,21/1981 w- 24. 1.16 9/22,23/1917 c+ 1.65 5/15/1911 1.16 12/22,23/1955 c+ 5. 1.62 6/10,11/1976 w+ 1.15 6/18,19/1916 c+ 6. 1.61 8/13/1979 c 25. 1.15 5/20,21/1932 w- 7. 1.53 10/27,28/1912 w- 26. 1.14 4/13,14/1973 8. 1.52 5/11,12/1900 w+ 27. 1.13 10/4/1923 w+ 9. 1.51 5/22,23/1942 w- 1.12 10/18,19/1899 c- 10. 1.50 6/3,4/1908 28. 1.12 3/7,8/1943 c+ 11. 1.48 1/17,18/1953 w 1.11 6/10/1977 w+ 1.48 5/11,12/1958 w- 1.10 6/7,8/1911 w+ 1.48 1/17,18/1953 w 1.10 11/3,4/1938 c+ 12. 1.45 6/6,7/1941 w+ 29. 1.10 4/30/1983 w+ 13. 1.41 5/22/2010 w- 30. 1.09 5/18,19/1921 c+ 14. 1.39 10/10,11/1911 w+ 1.09 4/26/2012 15. 1.36 1/21,22/1903 w 31. 1.08 10/3/1901 w+ 1.36 2/4,5/1907 c- 32. 1.07 5/27,28/1964 c 16. 1.31 10/6,7/1913 w+ 33. 1.06 4/26/1956 c+ 1.31 9/22,23/1918 w- 1.06 10/11,12/2000 c 17. 1.30 6/14,15/1925 w+ 34. 1.04 4/19,20/1904 c+ 1.30 10/5,6/1925 w+ 35. 1.03 5/28,29/1953 w+ 18. 1.27 7/30,31/1912 w 36. 1.02 5/25,26/1980 w+ 19. 1.26 4/12,13/1912 w+ 37. 1.00 5/1/1950 c+ 20. 1.25 5/23,24/1962 c- 1.00 2/4,5/1951 c+ * 1.10" fell in 60 minutes & There were breaks up to several hours between showers. NOTE: The above sequence is complete and includes only those rain events where not more than a trace of snow fell. At least 90% of all heavy 24-hour precipitation events had no measurable snow. The record prior to 1899 is incomplete and includes the following: 1. 2.72 3/5,6/1871 2. 2.50 11/1873 (exact date unknown) 3. 2.22 1/1875 " 4. 1.84 12/1871 " 5. 1.73 2/1872 " 6. 1.35 9/1893 " Joel Tannenholz...March, 1987 After taking numerous calls regarding the maximum intensity rainfall received at Boise, I aked for help from John Gilbert. He helped me find some rainfall intensity information for other people also. I'm keeping this information handy in the hydro cube, but I'll pass it along to everyone else, too. Since 1930, (before that we're not sure about intensity measurements) September 11, 1976 [tropical storm Kathleen] had the most intense rainfall. At Boise: 5 mins 0.26 inch 10 mins 0.51 inch 15 mins 0.69 inch 30 mins 1.00 inch 1 hr 1.12 inch 2 hrs 1.16 inch 3 hrs 1.21 inch Hopefully this information will help others answer those hard to answer questions from engineering firms when they are designing storm sewers. The second most intense measurements occurred in May of 1942. Amounts were: 5 mins 0.34 inch 15 mins 0.37 inch 30 mins 0.38 inch 1 hr 0.49 inch This storm was more intense for the 5 minutes, but it did not have the duration that the 1976 storm had. Just thought you would all find this information useful. Mary Mellema...April 20, 1994 The Great Labor Day Downburst September 7, 1998 A small but powerful thunderstorm rampaged through the neighborhoods adjacent to Gary Lane in northwest Boise during the afternoon of Labor Day between 5:25 pm and 5:50 pm MDT. George Skari, who lives at 5492 Riffle Way, measured .92 inch of rain in 12 minutes. Street and yard flooding resulted. George estimated wind gusts up to 60 mph. Numerous trees and fences were downed, and the roof of Shadow Hills School was damaged (damage to vents and air con- ditioner). Other reports from the storm: . Flooding near Franklin and Franklin Park . Structure fire on Oakhurst due to lightning strike . Power outages in downtown Boise . Mud slides at Pierce Park...Cartwright Hill and Eugene . Downed trees across State Street and Glenns Ferry... Highway 55 and Hill Road . Downed trees at Hill Road and Bogart...Warren and Manitou The storm was very selecitve. The airport measured only .26 inch. Neighborhoods south of Franklin and east of Cole experienced minor street flooding, while just west of Cole only traces of rain fell. There was no wind damage in any of those areas. 5/4/2012 c = la nina w = el nino weak c- or w- moderate c or w strong c+ or w+ boise heaviest rain events.txt