Are you ready for flood season?

November is historically the wettest month of the year in Western Washington and flood season usually continues into March.

So now is a good time to review a number of key flood related topics before the first flood event of the season arrives. First, some terminology. What is flood stage? That is the water level when the river begins to create some public threat such as cover some roads and threaten property. Flood stage at river forecast points are reviewed each year with local authorities since rivers do evolve and conditions in the rivers change.

There are three flood categories. Minor flood category is flood stage where relatively minor flood impacts occur. The next category is moderate – where river waters rise to the point where some inundation of structures occurs and some evacuations are needed. The final category is major flood. This category does not happen very often and involves extensive inundation of property and significant evacuations are needed.

The National Weather Service (NWS) has over 40 river forecast points in Western Washington. These locations represent a stretch of the river. River forecasts for these locations are available via the NWS Advanced Hydrologic Prediction Service. Visit NWS Seattle to find the river forecast point near you for the latest readings and forecasts. Flood stage and flood categories are listed there along with historical flood information as well.

The latest winter weather outlook from the NWS’s Climate Prediction Center anticipates a quite warm or strong El Nino for this winter season. The history of western Washington flooding during El Nino winters indicates flooding often occurs yet tends to involve only minor flooding. Significant widespread flooding can occur, but it less often compared to La Nina or neutral winters. The last significant flooding during an El Nino winter occurred in November of 2006.

El Ninos often bring above average temperatures and that is the outlook for this winter. Warmer temperatures mean, on average, a higher snow level that translates into a less than average mountain snowpack. Yet a repeat of last winter’s meager snowpack is not anticipated. This winter’s mountain snowpack should be much better than last winter, though still likely below average by next spring.

What can you do to get ready for flooding? For tips on what to do before, during and after a flood, visit NWS Flood Safety Turn Around Don’t Drown. The number one cause of flood related fatalities is people driving through or walking on water covered roadways. A couple of feet of moving water can easily lift and sweep a vehicle away.

In addition, the Take Winter By Storm preparedness campaign underway right now offers a number of flood and winter weather readiness tips and information.

Pacific Northwest NWS offices are conducting a Pacific Northwest Winter Weather Awareness Week from November 1 through the 7. Flooding is among the winter weather hazards addressed.
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