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The Willamette Valley Flood of November 1996

(didn't we do this last february )

We could see it coming

Update for Nov 20:

The worst is clearly over. No new flood warnings have been issued. Flooding on the Willamette upstream from Harrisburgh is expected to be fairly minimal today. Cold air has rapdily moved in to stabilize snow melt which is keeping the Santiam river from becoming the source of the upstream flooding as it was in February.

Some of you may be wondering what's up with the weather this year to have produced two such extreme events. That's a good question. There are sound scientific reasons to believe that this is more than just a statistical quirk. It may be related to changing jet stream patterns as we alter the heat balance of the earth through global warming --> most of that goes into heating the oceans. Stay tuned ...

Some Images are available here

This resource is under construction. It will contain official information from the National Weather Service, the Army Corps of Engineers and other such federal agencies. Here you will find the latest weather forecasts, weather warnings, flood warnings, river levels as well as an explanation of what caused this event and what the near future may hold. The material is somewhat disorganized but this is a near real-time resource! There are also likely to be spelling errors and other typos.

Current Weather Situation

Local Forecast: 

Weather Conditions at 9 AM PST on 19 NOV 96 for Eugene, OR.
Temp(F)    Humidity(%)    Wind(mph)    Pressure(in)    Weather
========================================================================
   57          93%          SSE at 18       29.23      light rain

SOUTHERN WILLAMETTE VALLEY INCLUDING EUGENE
1000 AM PST TUE NOV 19 1996

 TODAY...RAIN CHANGING TO SHOWERS. HIGHS IN THE UPPER 50S. WIND
BECOMING SOUTHWEST 15 TO 30 MPH.
 TONIGHT...SCATTERED SHOWERS. LOWS IN THE MID 30S. EVENING SOUTHWEST
WIND 10 TO 20 MPH.
 WEDNESDAY...SCATTERED SHOWERS. HIGHS 45 TO 50.
 <                    TEMPERATURE     /    PRECIPITATION
EUGENE                59  34  48      /    100  50  40

Latest Weather Warnings

Road Conditions:

River Levels:

What happened to cause this flood event:

A very unusual jet stream split focussed a hell of a lot of moisture at Southern Oregon. Some satellite loop images referenced below effectively show this. Basically, a cold polar jet coupled with zonal flow brought cold here as far south as Portland and produced snow from Portland to Seattle. To the south or Portland, a strong sub-tropical jet was tightly coupled to the east-west flow of the Jet Stream. This produced essentially a stationary front and cold rain pummelled the entire Southern Oregon area for about 24 hours. The largest rainfall recorded in this 24 hour period was in Lawson Creek at 19 inches . Eugene received about 5 inches during this period. By early Tuesday morning, the warm front associated with the sub-tropical jet had reached the southern willamette valley. The freezing level measured over Salem this morning was 9200 feet. Rapid snow melt will hence contribute to the runoff. This coupling of the sub-tropical jet to strong zonal flow is what caused the December 1964 flood. The main difference this time is reduced snowpack at higher elevations and the fact that cold air should rapidly be moving in to stablize melt at higher elevations.

What to Expect in the Near Term Future

The situation is somewhat unpredictable. A lot depends on how fast the warm front moves north and how fast the cold air replaces it thus stabilizing the snowmelt. Since this is only mid November the snow pack is less than it would be mid winter. This means that large scale flooding on the major rivers should be less than was observed last February. However, small scale flooding is likely to be worse in some areas due to 1) increased sediment load and stream channel changes from last february and 2) the tremendous amount of 24 hour rains that hit already saturated ground in Southern Oregon.

How are the Reservoirs Holding Up

The main control points on the Upper Willamette Basin are nowhere near capacity. Currently the Army Corps of engineers have a 4:1 release rate. Meaning that water is flowing into the reservoir at a rate which is 4 times greater than that which is being released. At last report, Doreena and Cottage Grove were 20-25 feet below capacity so there is ample room to accomodate the increased intake.























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