Overview

March was a rather cool month throughout Oregon. Precipitation totals were about equally divided between above- and below-normal monthly totals, but most values were reasonable close to normal. Oregonians eagerly await the arrival of warm, dry weather, and we think it will arrive very soon!

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 March 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 March 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 forecast for April-June (see maps below) suggests an equal chance of above-, near-, and below- temperatures and precipitation. Oregon Climate Service continues to predict a warmer and drier than average period during those months.

ENSO Update

World Meteorological Organization (WMO)— http://www.wmo.ch/index-en.html
March, 2006
Since around the turn of the year, sea-surface temperatures (SSTs) in the central and eastern equatorial Pacific have ranged between half and one degree Celsius below normal. Combined with broader tropical Pacific Ocean and atmosphere conditions, this is consistent with the early stages of a basin-wide La Niña event. However, the development of basin-wide La Niña conditions at this time of the year is highly unusual, hence there is some additional uncertainty over the extent to which typical La Niña rainfall and temperature patterns will occur for this event. Furthermore, the La Niña conditions are expected to be relatively short-lived, with a return to neutral conditions across the equatorial Pacific likely by mid-year or shortly thereafter.

At this time of the year, a continuation, or persistence, of prevailing conditions in the tropical Pacific is least likely, with the March to May period often witnessing marked transitions between phases of El Niño/La Niña. Although most computer models and expert interpretation project La Niña conditions to continue, at least through the next couple of months, a return to neutral conditions is considered most likely by mid-year. As predictions are least reliable at this time of year, careful monitoring will be needed over the next several months for indications of La Niña conditions persisting further into the year, or of the onset of a rapid evolution toward El Niño conditions. Neither of these two scenarios is considered likely, but cannot be ruled out at the current time.

SSTs first became colder than normal close to the South American coast in September 2005. This likely influenced local climate patterns through the latter months of 2005, but did not at that time constitute a basin-wide La Niña event. While conditions remained mostly neutral in the central equatorial Pacific, SSTs in the western equatorial Pacific were, and have continued to be, substantially warmer than normal. Combined with ocean patterns in the Indian Ocean, this situation continues to contribute to unusual and, in places, very damaging climate conditions in surrounding continental regions of the western Pacific and the Indian Oceans.

“It Rains All The Time”

We all know that rain occurs frequently in western Oregon. When it comes to the number of rainy days in an average year, the coastal Northwest is among the nation’s leaders. Here in the mid-valley we average about 160 wet days a year – nearly half of all days are wet. Most of these occur in the cool season: 126 of the 160 wet days are observed between October and April, on average. Thus, between October and April we get rain on 60% of all days, while for the May-September period it rains less than one-fourth of the time.

By the way, I recognize that not all readers live in western Oregon, but I’ll use it as one of the benchmarks because I do! And I’ll reference the local station several times, for several reasons: (1) it’s local! ; (2) it’s a long-term station (since 1889) located in a rural area that hasn’t seen much change; (3) the observers, especially Richard Mattix, almost never miss an observation, and the quality of the data they collect is second to none.

One aspect of rainfall in the Northwest is that rain tends to last a long time be relatively gentle – “long but not hard.” We seldom get a “cloudburst” of high intensity rain, and if we do it never lasts very long.

At locations that measure rainfall on an hourly basis in the Willamette Valley, the all-time records are a little over one inch per hour. That’s pretty intense, and would seem remarkable to us. Yet consider this: on July 4, 1956, Unionville, Maryland received 1.23 inches of rain. No big deal? Well, that amount occurred in one minute! Now THAT’S a cloudburst!

Bend, Oregon averages about 12 inches of precipitation a year. On June 22, 1947, Holt, Missouri received 12 inches of rain in 42 minutes! The world record for one hour is 15.78 inches in Inner Mongolia in 1977.

In Corvallis-Albany the average annual precipitation is about 43 inches. That amount fell on Alvin, Texas in only 24 hours, during Hurricane Claudette in July, 1979.

Our local record for rainfall in one day is 4.45 inches, set on November 18-19, 1996. I remember that day well. It rained really hard all day and all night, and significant local flooding occurred. That storm produced Oregon’s all-time one-day record, 11.65 inches near Port Orford.

Now consider this: in January, 1966 at Foc Foc on the Indian Ocean island of Reunion, 72 inches of rain fell in one day. Think about that: 3 inches an hour for 24 hours. Fortunately Reunion is a sandy volcanic island with very good drainage, or the flooding would have been legendary.

The most rain the mid-valley ever had in a single calendar month was 18.28 inches in November, 1973. The Oregon record is 57 inches at Glenora (near Tillamook) in 1909. The world record? How about 366 inches in Cherrapunji, India, in the Himalaya foothills, in July, 1861?

Our wettest single year was 1996, when the Corvallis-Albany station received a little over 73 inches. The Oregon record was set the same year – 206 inches at Laurel Mountain in the Coast Range. The latter is also the one-year record for any station in the continental U.S.

Compare that with Cherrapunji, which received 1,042 inches of rain in the 12 months between August 1860 and July 1861. Since Cherrapunji is affected by the Indian monsoon, most of that fell during just half the year. The big July month mentioned above was included.

Doubtless some of you enjoy “gullywashers,” and I wouldn’t mind experiencing a record-setting rainfall event, just once, to see what it’s like. But on a day-to-day basis I greatly prefer the frequent-but-gentle rains that characterize our local climate.

Out on a Limb with a Super El Niño Prediction
Roger Pielke Jr., R.: http://sciencepolicy.colorado.edu/prometheus/archives/climate_change/000771out_on_a_limb_with_a.html
I’m not really sure what to make of this, other than there is a dark line being drawn in the sand by NASA’s Jim Hansen and colleagues:

We suggest that an El Nino is likely to originate in 2006 and that there is a good chance it will be a "super El Nino", rivaling the 1983 and 1997-1998 El Ninos, which were successively labeled the "El Nino of the century" as they were of unprecedented strength in the previous 100 years.

Here is what NOAA/NCEP/CPC says:

Most of the statistical and coupled model forecasts indicate ENSO-neutral conditions in the tropical Pacific through the end of 2006 (Fig. 6). The spread of the most recent statistical and coupled model forecasts (weak La Niña to weak El Niño) indicates uncertainty in the outlooks for the last half of the year. However, current conditions (stronger-than-average easterly winds over the central equatorial Pacific and below-average upper-ocean heat content) support those forecasts indicating that La Nina conditions will continue for the next 1-3 months.

It would of course be incorrect to evaluate the science underlying a single prediction based on a single forecast. Nonetheless, the reality is that Dr. Hansen has bet some of his public credibility in making such a forecast, for better or worse. If he is proven right with this forecast, contrary to all of the models and statistics, then his credibility will rise far beyond its already stratospheric levels. If he is wrong, he will be brought a bit back to Earth by his critics who will use this against him. In short, he is taking a big risk, with potential for a big payoff or a big cost. A final note worth thinking about – a strong El Niño event is typically inconsistent with a very active hurricane season, so if Dr. Hansen is proven right, then a bunch of other folks will likely be wrong (including Bill Gray, NOAA, and others who are anticipating another active hurricane season). Time, and not much of it, will tell.