Overview

The first half of February was rather dry, but cold; the second half was much wetter and somewhat milder. Overall, the month was wetter than average in most parts of the state. Temperatures were generally below average on the coast and at higher elevations and above average elsewhere.

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 February 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 February 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

TThe Climate Prediction Center’s (CPC) forecasts for March-May appear below. Temperatures for Oregon show a slight tendency toward above normal temperatures, 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 ---basically agreeing with CPC.

ENSO Update
1. From the Bureau of Meteorology (BOM) of Australia, March 7, 2007
“The eastern equatorial Pacific Ocean has continued to cool rapidly following the demise of the El Niño event. While current conditions are neutral, the cooling has increased the likelihood of, though not guaranteed, a switch to La Niña conditions over the coming months. The Trade Winds have mostly been close to or somewhat stronger than normal since December, the SOI has been neutral for three of the past four months and is now close to zero and cloudiness has shifted to the western Pacific. There would now appear to be little chance of a return to El Niño conditions in 2007, with a continuation of neutral, or a switch to La Niña conditions, the more likely scenarios.

“ What does this mean for Australia? Firstly, whilst a rapid cooling of the Pacific at the end of the El Niño would normally be associated with a return to more normal, or in some cases above normal rainfall patterns, it is unlikely such rain will be enough to make up for the long-term drought through eastern and southern Australia. This particularly applies to water supplies, which in some instances require several years of healthy rainfalls to recover to a satisfactory level. Nonetheless, we continue to be cautiously optimistic that there will be a general easing of dry conditions in drought-affected areas over the next one to two seasons.”

A La Niña in 2007?

“ The chance of a La Niña developing in 2007 is thought to be higher than the long-term average (which is about one in five or 20%) because (a) they have a tendency to follow an El Niño; (b) the El Niño has decayed somewhat earlier than normal thereby giving time for a La Niña to begin developing during the critical March to June period; and (c) a large pool of cold sub-surface water remains in the central to eastern tropical Pacific Ocean and is starting to affect surface temperatures in the region. La Niña events are generally associated with wetter than normal conditions across much of the eastern half of the country from about autumn. Computer models generally indicate further cooling in the Pacific Ocean.”

2. El Niño/Southern Oscillation (ENSO) Diagnostic Discussion
Climate Prediction Center/NCEP, 3/8/07

“ The pattern of anomalously warm SSTs associated with El Niño disappeared from the equatorial Pacific east of the date line during February. By the end of the month, SSTs were near average in the vicinity of the date line, and below average over the eastern equatorial Pacific between 140°W and the west coast of South America.

“ Also, the main area of anomalously warm SSTs along the equator had become centered well west of the date line, which is also consistent with the disappearance of El Niño. The latest weekly SST departures have decreased to near 0.5†C in the Niño 4 region and to near 0 †C in the Niño 3.4 region, and have become slightly negative in the Niño 3 and Niño 1+2 regions. Accompanying this drop in SST anomalies, the equatorial upper-ocean heat content (average temperature departures in the upper 300 m of the ocean) decreased rapidly during December 2006-January 2007, as the upper ocean cooled and negative temperature anomalies developed (see figure below). These trends in surface and subsurface ocean temperatures indicate that the warm (El Niño) episode has ended and that conditions are becoming favorable for La Niña to develop.”

Anomalous equatorial upper-ocean heat content averaged over the longitude band 180†-100†W. Heat content anomalies are computed as departures from the 1982-2004 base period means.

Volcanoes and Climate
George H. Taylor
Most of the statistical and coupled models, including the NCEP Climate Forecast System (CFS), indicate additional anomalous cooling during the next 2-3 months. Some of the forecast models, especially the CFS, indicate a rapid transition to La Niña conditions during March-May 2007. This scenario is supported by the latest surface and subsurface oceanic conditions, and the persistence of stronger than-average low-level easterly winds over the central equatorial Pacific.

When I give public talks, I usually talk about “things that affect climate.” One of the questions frequently asked by someone in the audience is, “do volcanoes affect climate?” The answer is a qualified “yes,” because some of the evidence is circumstantial and a volcano-climate connection can be tough to prove.

The effects also depend on the location and character of a volcanic eruption. Generally speaking, tropical volcanoes that emit a large quantity of dust and fly ash have the biggest effects on climate.

One such volcano erupted in 1982 in Mexico. It was called “El Chichon,” and it was the first major eruption to have its atmospheric effects studied in detailed by modern instruments. Although the volume of the eruption was small (about the size of the Mt. St. Helens eruption), El Chichon released an unusually large volume of dust and ash, which contained large quantities of sulfate, a substance that affects climate by reflecting sunlight. El Chichon’s dust caused the stratosphere to warm, the Earth’s surface to cool, and may have contributed to the huge 1982-83 El Nino, one of the biggest in history.

Much earlier, the Tambora (1815) and Krakatoa (1883) eruptions caused significant worldwide effects. But in modern times, the Mt. Pinatubo event in the Philippines was the most important. Pinatubo’s 1991 eruption was the second largest of the 20th century (trailing only Mt. Novarupta, Alaska, in 1912). Pinatubo released so much ash and dust that sunrises and sunsets were unusually colorful for several years, and global temperatures cooled. In 1992 and 1993, the average temperature in the Northern Hemisphere was reduced by about 1°F and the entire planet was cooled by .75°F. Pinatubo may have also been responsible for what may have been the strangest weather year Oregon (and the U.S.) ever had.

First came the drought. Following seven straight drier than normal years, the very dry winter and spring of 1992 were devastating. A statewide drought was declared in Oregon and adjacent states. Water was rationed. Lake levels were very low. Wells ran dry. Agriculture suffered. Trees, weakened by drought, succumbed to pests and diseases.

A relatively dry fall and early winter later that year did little to promote optimism. And then came the cold. January of 1993 saw temperatures in the mid-valley dip as low as 10°F. Snow fell, and remained on the ground throughout the month.

Cold and ice persisted into February. Then, on the 18th and 19th, one of the biggest 24-hour snow events ever seen here dropped 12 inches of snow. And then the air warmed, the snow melted, and spring arrived.

Water supply folks were nervous. The winter had been much drier than average. Predictions of a summer drought were rampant. Things were looking even worse than they had in 1992.

And then came the rains. Beginning in mid-March, rains soaked the Northwest. April was as wet as an average January. May was almost as wet. June and July were wetter than average. All told, it was the wettest spring western Oregon ever had. For the months March through July, we received more than 19 inches; in an average year, we get about 11.

Water supply worries vanished. Instead, folks wondered “what happened to spring?” and “if it’s summer, why is it so cloudy and cool?” On the other hand, allergy sufferers rejoiced because the wet weather kept the pollen counts way down.

Meanwhile, to the east, even bigger events were happening. In March, the famous “Storm of the Century” struck the eastern U.S. Record low pressures, wind speeds, low temperatures and large snowfall amounts were recorded. More than 250 people were killed and 25% of the United States' airline flights were cancelled for two days.

Not to be outdone, the Midwest saw record-setting flooding in July, in what was one of the most significant and damaging natural disasters ever to hit the United States. Damages totaled $15 billion, 50 people died, hundreds of levees failed, and thousands of people were evacuated, some for months.

All that in the space of 12 months. Drought, ice and snow, wettest spring ever, and two really huge regional events. Did Pinatubo cause these, or contribute to them? It’s a tough question to answer, and a difficult hypothesis to prove.

But my answer would be that it probably did.