Overview

December started wet, but quickly turned dry. A nearly two-week dry spell caused a stirring of “water worries.” But just after mid-month, the rains came. And came. And came.

By the second week in January, the rains were continuing, causing significant flooding in much of the state. More on that next month. But the very wet end of December enabled nearly every station in the state to exceed the monthly normal (see Table 3). Furthermore, the vast majority of Oregon stations are above normal for the Water Year – just about as far above normal, in fact, as they were below normal last winter. What a difference a year makes!!

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 December 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 December 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 January-March appear below. Temperatures for western Oregon are likely to be above normal, with equal chances of above-, near- and below-normal temperatures east of the Cascades. Precipitation probabilities show equal chances of above-, near-, and below-normal.

Oregon Climate Service predicts above-normal temperatures and above-normal precipitation for the next three months, followed by a relatively dry and mild spring.

EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION
CLIMATE PREDICTION CENTER/NCEP
January 12, 2006

Equatorial SST anomalies greater than +0.5†C were restricted to the region between Indonesia and 165†E during December, while negative anomalies less than –0.5†C were observed at most locations between the date line and the South American coast. By the end of the month the SST departures were negative in all of the Niño regions. During the last several months surface and subsurface temperature anomalies have decreased in the region between 180†W and the South American coast. During the same period persistent stronger-than-average low-level equatorial easterly winds were observed over the central Pacific. Since early November there has been a persistent pattern of enhanced tropical convection near 130†E (Indonesia) and suppressed convection near the date line (180†W). Collectively, the present oceanic and atmospheric anomalies are consistent with the development of La Niña conditions in the tropical Pacific.

Over the past several months most of the statistical and coupled model forecasts have trended towards cooler conditions in the tropical Pacific through mid-2006. The spread of the most recent statistical and coupled model forecasts (weak La Niña to ENSO-neutral) indicates some uncertainty in the outlooks. However, current conditions (stronger-than-average easterly winds over the central equatorial Pacific) and recent cooling trends in observed oceanic conditions support the continuation of La Nina conditions in the tropical Pacific during the next 3-6 months.

Lots and Lots of Wet Days…

In meteorology, we define “precipitation” as “water falling from the sky” in its various forms, including rain, drizzle, snow, hail, and several others. Precipitation is measured by its liquid water content, so in the case of snowfall the snow is melted prior to being measured. In the U.S., at least one one-hundredth of an inch (.01”) must occur before precipitation is considered “measurable”; a day with .01” or more is often called a “wet day.”

We’ve endured a lot of wet days recently, and it may seem like we’ve had the Biblical “40 days and 40 nights,” but it’s actually nowhere near that. However, if not for a dry day on January 5 we would have over 25 by now. The mid-valley record is 40 days, set in 1983 (November 6-December 15). Our records go back to 1889.

Meanwhile, our neighbors to the north are counting the days and watching the skies. Seattle’s all-time record for consecutive wet days is 33, set in 1953. At press time (Jan. 12) they were up to Day 25. They may make it.

Portland’s record is 29 straight days, set in January, 1950, but this record is “tainted.” January, 1950 was the snowiest month the Willamette Valley ever had. Portland had measurable snow on 21 out of the 31 days, and when it wasn’t snowing there was cold rain. Out Portland’s 29 wet days, 20 were snowy.

Corvallis reported a total of 51 inches of snow that month, far more than any other month in history. Other stations reported even more. Cottage Grove Dam, at 823 feet in elevation, totaled 121.5 inches for the month. Bend had 56 inches. Crater Lake reported 313!
Returning to Portland and its rainfall records, we find that the longest stretch of RAINY days was 24, in January, 1965. This is for Portland Airport, whose records extend back to 1941.

Salem, whose data go back to 1892, had 33 consecutive wet days in January 1950 – here we go again – with a record for consecutive RAINY days of 31, in February-March 1919.

What really surprises me is Eugene’s record. Granted, it’s been in existence for a shorter time than the other stations (since 1939). But the longest string of consecutive wet days is only 19, set in January 1946, December 2001, … and January 1950.

Since Portland, Salem and Eugene all had a dry day earlier this month, none of them are threatening the records. Ditto for central and eastern Oregon sites, which are in drier locations anyway.

A Look Back at 2005

It’s time to look back on a rather interesting weather year in the mid-Valley. Around here we seldom get an “average” year – our averages are made up of wet years and dry years that offset each other, as well as warm years and cool years. The year 2005 was not in any way “average,” but it sure was interesting.

The year began dry and cool, following dry and cool months of November and December. I remember thinking, “We’ve had two dry months in a row. Things HAVE to change soon!” But January had less than half the monthly average rain. And much to my surprise and chagrin, February was even worse. Only .47” of rain fell, the third driest February in history (our records extend back to 1889). This year’s dryness was surpassed only 1920’s .12” and 1929’s .36”.

Things looked bleak. Many folks, including the National Weather Service, were forecasting severe drought conditions during summer. But based on the indications I was seeing, I thought differently.

In February I attended an Oregon Drought Council meeting (I’m a member). Unlike many of our meetings, this one was of great interest to the media. A TV crew put a Weather Service guy on camera and asked him what was going to happen and he said “continued dry, with severe drought conditions developing.” Then they asked me, and I said, “I think spring is going to be quite wet.” Call it wishful thinking, call it foolish…but I sure HOPED it would come true.

It did. Rains began in mid-March (simultaneous with the beginning of spring break and the Governor’s declaration of a statewide drought) and didn’t let up until early July. Farmers, gardeners, and baseball players were disappointed, but the good news was: we avoided a drought! Lakes filled, ground water was recharged, water supplies were adequate – and none of that looked possible in February.

Summer was a little warmer than average, especially during the typical “hottest time of year” -- mid-July through mid-August. There were 18 days with temperatures in the 90s (in an average year we get 11), but no 100+ days (the warmest was 98 on the afternoon of August 4). September was very pleasant and rather dry.

And then came fall, and a curious pattern developed. Most of October was on the dry side, but a wet period at the beginning of the month and another one at the end pushed our monthly total above the October average. November had a lengthy dry spell in the middle of the month, but again saw a very wet beginning and end of the month and ended up near average. And December? Very wet in the first week, and then dry and quite cold for 2 weeks. Total precipitation for the period December 5-18 was only .02” (mostly fog drip, I suspect).

And then came the rains. In the last 13 days of the month we have received more than an entire month’s worth of rain. Local flooding is occurring. Nobody is talking drought.

One other pattern has emerged here. Each of the last 4 years has seen very cold temperatures in late October or early- to mid-November.

This year we got down into the 20s in mid-November, with consecutive days of 26, 26, and 27 degrees – very cold for that early in the season. This is a phenomenon reported in other parts of the west: fall coning earlier, at the same time that spring seems to be coming earlier.

For early 2006, expect the mild, wet weather to continue. And I’m expecting spring to be a lot drier and warmer than last year. The farmers, gardeners, and baseballers will rejoice if that happens.

Happy New Year, one and all!

Oregon Climate Service

George H. Taylor, Oregon State Climatologist

Wayne P. Gibson, Programmer/GIS mngr.

Eileen Kaspar, Research Assistant/Manager of Data Services

Melanie Mitchell, Undergraduate Assistant

Wolf Read, Undergraduate Assistant

Emily Gibson, Student Assistant

Cadee Hale, Publications Assistant

Sara Joos, Student Assistant

Sean Daly, Student Assistant

Kirk Borgerding, Undergraduate Assistant

Kelsey Kuykendall, Undergraduate Assistant

Oregon Climate Service, Strand 326,                             	     Phone: (541) 737-5705  
Oregon State University                                                      Fax: (541) 737-5710   
Corvallis, Oregon  97331                                                     E-mail: oregon@coas.orst.edu   
                                                                             Web: http://www.ocs.oregonstate.edu