Overview

What a month! A dry, mild October gave way suddenly on November first to a wild, wet, windy month. The record-setting wet weather in the first 10 days of the month gave way to a major wind storm (which knocked down trees and closed some roads), followed in turn by an unusual (for November) low-elevation snow event, followed by still more rain. Whew!

Table 1 is a summary of monthly averages and totals at selected stations throughout the state. Table 2 lists daily temperatures and precipitation for most of the locations listed in Table 1. In Table 3, monthly and seasonal precipitation totals throughout the state are listed.

Basin Summary

Here is a summary of water indicators at the end of the month, by river basin:

n.a. Not available
(1) Percent of normal November precipitation, from NOAA Cooperative sites
(2) Percent of normal seasonal precipitation (since Oct. 1), from NOAA Cooperative sites
(3) Percent of normal seasonal precipitation, from Natural Resources Conservation Service (NRCS) SNOTEL sites
(4) Percent of normal snow water equivalent, from NRCS SNOTEL sites
(5) Percent of normal November stream flow, from U.S. Geological Survey (USGS)
(6) Percent of normal seasonal stream flow (since Oct. 1), from USGS
(7) Surface Water Supply Index, from NRCS (-4 = very dry, 0 = normal, +4 = very wet)

Forecasts

The Climate Prediction Center’s (CPC) forecasts for December-February appear below. Temperatures for Oregon (and much of the northern half of the U.S.) are likely to be above normal, while precipitation probabilities show equal chances of above-, near-, and below-normal.

Oregon Climate Service predicts above-normal temperatures and normal precipitation for the next three months.

ENSO Update
Australian Bureau of Meteorology, December 5, 2006
El Niño conditions continue to dominate the equatorial Pacific Ocean. Ocean surface temperatures have continued to warm, and are now more than 1°C above average right across the central and eastern equatorial Pacific Ocean. Strongest recent warming has occurred in areas near the dateline, supported by slightly weaker than average Trade Winds and above normal cloudiness in this region. Equatorial Pacific subsurface temperatures also remain warm. The 2006/07 El Niño is entering its mature phase, when the Pacific ocean temperatures, winds and cloud patterns reinforce each other. Computer model guidance continues to suggest that Pacific Ocean temperatures, and hence the El Niño, may peak around January or February 2007. This timing would be consistent with the breakdown of past El Niño events.

In the eastern Indian Ocean, waters which have been cool since June, warmed to near normal during November. Cool conditions in this region have also been linked to reduced rainfall over southern and eastern Australia.

CPC ENSO Forecast (December 7, 2006)
El Niño conditions are likely to continue through May 2007. Equatorial Pacific SST anomalies greater than +1șC were observed in most of the equatorial Pacific between 170șE and the South American coast. The latest SST departures in the Niño regions are between 1.1șC and 1.3șC, except for Niño 1+2. The increase in SST anomalies during the last several months has been accompanied by weaker-than-average low-level equatorial easterly winds across most of the equatorial Pacific and negative values of the Southern Oscillation Index (SOI). Collectively, these oceanic and atmospheric anomalies are consistent with the early stages of El Niño in the tropical Pacific.

Record-setting Rain Storms in a Record-Setting Month
George Taylor and Cadee Hale
Following an unusually dry and sunny late summer and early autumn, Pacific Northwest weather changed dramatically in early November as a series of strong, wet storms began to affect the region. The most significant was a multi-day rain event caused by copious amounts of subtropical moisture, resulting in one of the wettest periods ever seen in the Northwest. Oregon, Washington and Idaho saw new 24-hour rainfall records set:

WASHINGTON
June Lake (elev. 3,340 ft.): 15.20 inches on November 6-7, 2006
Former Record: 14.26 inches on November 23-24, 1986 (Mt. Mitchell #2, elev. 3,600 ft.)

OREGON
Lee's Camp (elev. 660 ft.): 14.30 inches on November 6-7, 2006
Former Record: 11.65 inches on November 19, 1996 (Port Orford, elev. 150 ft.)

IDAHO
Bear Mountain (elev. 5,400 ft.): 9.40 inches on November 6-7, 2006
Former Record: 7.17 inches on November 23, 1909 (Rattlesnake Creek, elev. 4,000 ft.)

Numerous locations in northwest Oregon and southwest Washington reported more than 7 inches in a single day (most of them on November 6 or 7), as well as other very significant weekly and monthly totals. Table 1 below shows Oregon and Washington one-day totals exceeding 7 inches (not necessarily complete). Nehalem 9 NE, with the second highest one-day total for Oregon (11.77 inches) had a two-day total of 20.69 inches for the 6th-7th.

Table 1 – Daily Totals Over 7 inches

Many sites set new monthly records for any month of the year. Among them:

Table 2 – New Monthly Records

Other sites recorded new November records:

Table 3 – New November Record

A complete report, including satellite pictures and on-the-ground photographs, is at http://www.ocs.oregonstate.edu/page_links/whats_new/november_flooding.html