Record-breaking precipitation throughout much of Oregon caused local flooding, landslides, and power outages over much of the state during November 18-20. The rain resulted from a broad upper-air weather system of moist subtropical air which originated over the tropical Pacific. The air mass reached central California over the previous weekend, producing rainfall daily amounts as much as 8 inches. Gradually the system moved northward, reaching southwestern Oregon on the 17th and spreading to the remainder of the state the following day. High rainfall amounts were reported throughout the state.
The infrared satellite image for November 18 shows the areas of warm and cold air over the Northwest. To the north of the frontal boundary, the air mass was quite cool; snow was reported from Portland northward into Washington. South of the front, very mild air and heavy rains prevailed. Winds were also very strong, exceeding 70 mph at some coastal locations in southern Oregon.
Using a Log III Pearson analysis, we computed the return periods for daily precipitation amounts and created a map for western Oregon.
Records
All-time one-day precipitation records were set at many locations. Some of these included:
| location | amount (in.) | records began | old record (in.) | year set |
| Corvallis | 4.45
|
1889
|
4.28
|
1965
|
| North Bend | 6.67
|
1931
|
5.60
|
1981
|
| Portland | 2.70
|
1939
|
2.48
|
1948
|
| Redmond | 2.38
|
1948
|
1.81
|
1969
|
| Roseburg | 4.35
|
1931
|
3.28
|
1965
|
Daily and monthly records were set at many sites as well. At Portland Airport, 3.86 inches was recorded between 4 p.m. on the 18th and 4 p.m. on the 19th. This broke the November 24-hour total of 2.82 inches, which was set November 10-11, 1995. Doubtless when more observations are received, many additional records will become apparent.
River levels
As expected, rivers rose very quickly; many reached flood stage. Here are USGS hydrographs for several stations in Oregon:
Willamette River at Harrisburg
For the latest river and stream reports, check here.
Local Pictures
(Corvallis, November 20, 1996)
Highway 34, closed eastbound. Big image and Small image
Martin Luther King (Water) Park, east of the river.Big image and Small image
Willamette River (background) spills into MLK Park. Big image and Small image
Willamette River, with Corvallis in the background. Big image and Small image
Willamette River nearly overflowing westside bank. Big image and Small image
Willamette River, carrying lots of junk. Big image and Small image
The Corvallis BMX track (B as in boat?) Big image and Small image
Avery Park playground. Big image and Small image
George Taylor
State Climatologist
Oregon Climate Service
Local Pictures
(Corvallis, November 21, 1996)
Highway 34, closed eastbound. Big image and Small image
Highway 34, closed junction east of Corvallis. Big image and Small image
Under the junction from Hwy 34 to South Corvallis. Big image and Small image
Path swallowed by Willamette River. Big image and Small image
Path swallowed by Marys River.Big image and Small image
Willamette Park with the river high on its banks. Big image and Small image
Chris Hannan
Research Assistant
Oregon Climate Service
George Taylor, Oregon State Climatologist