The heavy rainfall in January 2009 damaged the Howard Hanson Dam (located on the Green River in King County). The water was stored in the dam at a record high elevation of 1189 feet resulting in two depressions in the right abutment of the dam. Measures have been taken to temporarily fix the damage, and communities potentially affected have been making preparations since the damage was first discovered. Still, the Army Corps of Engineers warn that increased flooding along the Green River Valley is possible as we enter this wet season because of the dam's reduced capacity for holding water in the reservoir. The forecast of an El Niño is good news for the residents in the Green River Valley because drier conditions in WA are usually associated with the warm phase of ENSO. That does not mean that we won't get heavy rain events that would cause trouble for the dam, however, as an El Niño simply tips the odds towards drier average weather.

Figure 1 shows a map of the stations in the vicinity of the Howard Hanson Dam, with some of them labeled. The dam and the reservoir are enclosed in the black box on the map. To find out more about the stations near the dam, visit our Climate Inventory Map.

Two stations near the dam (Cougar Mountain SnoTel and Landsburg COOP) report real-time precipitation data, and the accumulated precipitation for the 2010 water year (Oct 1, 2009 through Sept 30, 2010) will be plotted on this page compared to the 1971-2000 normal (Figures 2 & 3). The 2009 water year accumulated precipitation is also plotted for the Cougar Mountain station. This information will be updated in near real-time to monitor the precipitation in the dam vicinity compared to the 30-year normal.

Figure 1: Stations around the Howard Hanson Dam (enclosed in the black box). Selected stations are labeled. Please click on the figure to see the full-size image.

Figure 2: 2010 water year accumulated precipitation for Cougar Mountain SnoTel (green) compared to the 30-year normal (dashed black). The accumulated precipitation for the 2009 water year is also plotted (dashed blue). Please click on the figure to see the full-size image.

Figure 3: 2010 water year accumulated precipitation for Landsburg (green) compared to the 30-year normal (dashed black). Please click on the table to see the full-size image.