# Diablo Dam

Diablo Dam is one of three dams along the upper Skagit River in Whatcom County, Washington and part of the Skagit River Hydroelectric Project that supplies Seattle with some of its power needs. The dam was built in Diablo Canyon, a gorge of solid granite with vertical walls rising 160 feet (49 m) from the river bed, yet were less than 100 feet (30 m) apart. Construction began in 1927, and was completed in 1930. The dam began generating electricity in 1936.
The result was a power-generating dam that holds a reservoir known as Diablo Lake. At the time it was completed, Diablo Dam, at 389 feet (119 m), was the tallest dam in the world. Water from the dam operates two main generators, each with a capacity of 64.5 MW.48°42′51″N 121°07′52″W﻿ / ﻿48.7143°N 121.1312°W﻿ / 48.7143; -121.1312 The dam and its original associated power generation infrastructure were listed on the National Register of Historic Places in 1989.

## Climate

The Western Regional Climate Center (WRCC) reports weather station 452157 at Diablo Dam since 1948, presently at 48°42′51″N 121°08′35″W﻿ / ﻿48.71417°N 121.14306°W﻿ / 48.71417; -121.14306 with an elevation of 891 feet (272 m). The dam is in a transitional maritime-mediterranean climate (Köppen (Cfb/Csb) depending on summer rainfall isotherm.
Climate data for Diablo Dam, Washington (1991–2020 normals, extremes 1914–present) :
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Record high °F (°C) | 62 (17) | 63 (17) | 76 (24) | 90 (32) | 103 (39) | 110 (43) | 106 (41) | 106 (41) | 101 (38) | 87 (31) | 65 (18) | 59 (15) | 110 (43) |
| Mean maximum °F (°C) | 48.4 (9.1) | 52.7 (11.5) | 63.7 (17.6) | 75.9 (24.4) | 86.4 (30.2) | 90.8 (32.7) | 95.6 (35.3) | 94.8 (34.9) | 88.4 (31.3) | 72.7 (22.6) | 55.1 (12.8) | 48.5 (9.2) | 98.3 (36.8) |
| Mean daily maximum °F (°C) | 38.5 (3.6) | 43.2 (6.2) | 49.0 (9.4) | 57.2 (14.0) | 66.1 (18.9) | 70.3 (21.3) | 78.1 (25.6) | 78.8 (26.0) | 71.3 (21.8) | 57.5 (14.2) | 44.7 (7.1) | 38.1 (3.4) | 57.7 (14.3) |
| Daily mean °F (°C) | 34.0 (1.1) | 36.7 (2.6) | 41.1 (5.1) | 47.4 (8.6) | 55.2 (12.9) | 59.8 (15.4) | 65.8 (18.8) | 66.4 (19.1) | 60.1 (15.6) | 49.5 (9.7) | 39.8 (4.3) | 34.2 (1.2) | 49.2 (9.6) |
| Mean daily minimum °F (°C) | 29.5 (−1.4) | 30.3 (−0.9) | 33.1 (0.6) | 37.5 (3.1) | 44.2 (6.8) | 49.4 (9.7) | 53.4 (11.9) | 53.9 (12.2) | 48.9 (9.4) | 41.5 (5.3) | 34.8 (1.6) | 30.2 (−1.0) | 40.6 (4.8) |
| Mean minimum °F (°C) | 17.4 (−8.1) | 21.2 (−6.0) | 25.5 (−3.6) | 30.7 (−0.7) | 35.8 (2.1) | 42.5 (5.8) | 47.3 (8.5) | 47.3 (8.5) | 41.4 (5.2) | 31.8 (−0.1) | 24.4 (−4.2) | 19.1 (−7.2) | 11.2 (−11.6) |
| Record low °F (°C) | −2 (−19) | 0 (−18) | 9 (−13) | 24 (−4) | 28 (−2) | 33 (1) | 38 (3) | 37 (3) | 31 (−1) | 18 (−8) | 5 (−15) | −2 (−19) | −2 (−19) |
| Average precipitation inches (mm) | 12.25 (311) | 7.38 (187) | 8.16 (207) | 4.60 (117) | 2.71 (69) | 2.25 (57) | 1.25 (32) | 1.51 (38) | 3.41 (87) | 8.64 (219) | 13.66 (347) | 11.57 (294) | 77.39 (1,965) |
| Average snowfall inches (cm) | 12.2 (31) | 9.9 (25) | 4.2 (11) | 0.3 (0.76) | 0.0 (0.0) | 0.0 (0.0) | 0.0 (0.0) | 0.0 (0.0) | 0.0 (0.0) | 0.0 (0.0) | 3.1 (7.9) | 16.0 (41) | 45.7 (116.66) |
| Average extreme snow depth inches (cm) | 11.0 (28) | 7.7 (20) | 4.1 (10) | 0.1 (0.25) | 0.0 (0.0) | 0.0 (0.0) | 0.0 (0.0) | 0.0 (0.0) | 0.0 (0.0) | 0.0 (0.0) | 1.9 (4.8) | 9.7 (25) | 16.0 (41) |
| Average precipitation days (≥ 0.01 in) | 18.8 | 15.6 | 19.0 | 16.5 | 12.8 | 12.1 | 6.4 | 6.3 | 10.8 | 16.6 | 19.9 | 19.5 | 174.3 |
| Average snowy days (≥ 0.1 in) | 4.4 | 2.6 | 2.0 | 0.1 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 1.3 | 5.1 | 15.5 |
| Source 1: NOAA ||||||||||||||
| Source 2: National Weather Service ||||||||||||||