Overview

The first half of May was a continuation of March-April: wet and cool. Things changes significantly in the middle of the month, however, and the second half of the month was much warmer and drier than the first.

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. Figure 1 shows the percentage of normal precipitation for the Water Year.

Basin Summary

Here is a summary of precipitation, water supply, and snow pack as of the end of the month, by river basin:

	Precipitation			Stream Flow		SWSI
BASIN	(1)	(2)	(3)	(4)	(5)	(6)
OWYHEE	149	96	88	45	25	-1.5
MALHEUR	133	92	100	6	12	-1.4
GRAND RONDE, POWDER, BURNT	124	119	95	88	92	-0.7
UMATILLA, WALLA WALLA, WILLOW	72	103	95	73	102	-0.3
UPPER JOHN DAY	101	105	92	77	72	+0.3
UPPER DESCHUTES, CROOKED	97	89	84	50	63	-0.2
LOWER DESCHUTES, HOOD RIVER	75	101	84	76	75	0.0
WILLAMETTE	55	101	85	90	87	+1.8
ROGUE, UMPQUA	59	107	83	105	93	+0.7
KLAMATH	85	95	92	79	72	-1.1
LAKE COUNTY, GOOSE LAKE	89	97	88	83	40	+0.2
HARNEY	104	94	95	104	71	-0.4
NORTH COAST	63	95	n.a.	91	93	+0.4
SOUTH COAST	50	98	n.a.	113	108	+1.7

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)

Forecast

The Climate Prediction Center (CPC) predicts average temperatures and above-average precipitation for June; for the three-month period ending in August, there is a likelihood of average precipitation and average temperatures. Oregon Climate Service predicts above-average temperatures and below-average precipitation for June; for the three months we predict of average precipitation and average temperatures.

La Niña conditions appear to be developing in the Pacific. Stay tuned for news in the next several months.

COASTAL CITIES TURN UP THE HEAT ON RAINFALL

NASA, May 27, 2003

The old song, asking rain to "go away" and "come again another day," may get even older for people who live in large coastal cities, according to new NASA-funded research.

According to the study, urban heat islands, created from pavement and buildings in big coastal cities like Houston, cause warm air to rise and interact with sea breezes to create heavier and more frequent rainfall in and downwind of the cities. Analysis of Houston-area rain-gauge data, both prior to and since urbanization, also suggests there have been observed increases in rainfall as more heat islands were created.

Authors, J. Marshall Shepherd of NASA's Goddard Space Flight Center, Greenbelt, Md., and Steve Burian, a University of Arkansas, Fayetteville, Ark. researcher, believe the impact large coastal cities have on weather, and possibly climate, will become increasingly important as more people move into urban areas, with even greater concentrations in coastal zones. The paper is in the current American Meteorological Society and American Geophysical Union's journal, Earth Interactions.

A recent United Nations report estimates 60 percent of Earth's population will live in cities by 2025. Previous related studies have shown urban heat islands create heavier rainfall in and downwind of cities like Atlanta, St. Louis and Chicago. However, this is one of the first studies to provide evidence of such an effect around a U.S. coastal city. It is also the first to incorporate specific satellite-derived rainfall data for a coastal urban area.

Urban areas with high concentrations of buildings, roads and other artificial surfaces retain heat, which leads to warmer surrounding temperatures and creates heat islands. Rising warm air, promoted by the increased heat, may help produce clouds that result in more rainfall around cities. Buildings of different heights cause winds to converge, driving them upward, helping form clouds. The study shows the urban heat island/rain effect may be even more pronounced near coasts. In coastal cities like Houston, sea breezes also create rising air and clouds. The combination of urban converging winds and coastal sea breezes may enhance thunderstorm development.

"Recent publications have shown evidence of increased lightning activity over and downwind of Houston," Shepherd said. "Since lightning and rainfall are so closely related, we decided to use TRMM's Precipitation Radar, and a network of rain gauges, to see if urban-induced abnormal rainfall existed," he said.

Using data from 1998 to 2002, the researchers found mean rainfall rates, during the warm season, were 44 percent greater downwind of Houston than upwind, even though the regions share the same climate. They also found rainfall rates were 29 percent greater over the city than upwind. Rainfall rates indicate how hard it rains and can be an indicator of enhanced thunderstorm activity.

To rule out any effects from the coastline curvature near Houston on thunderstorm development, the researchers divided the entire Texas coast into seven zones extending 100 kilometers (62 miles) inland and

including four or five major inlets or bays. Analysis of rainfall data in these zones showed abnormal rainfall only occurred over and downwind of Houston, which suggested effects from the urban landscape were significant. At the coastlines, TRMM satellite data were important, because they allowed researchers to assess rainfall data in areas where there were no gauges and records, like over the ocean.

A companion paper by the researchers, presented in March at a Geological Society of America meeting in Kansas City, Mo., stated urban areas also affect the timing of rainfall. Compared to upwind areas, there were nearly two times as many occurrences of rainfall from noon to midnight in the urban area. This finding has significant implications for flood control in Houston, Burian said.

Wind Power in Oregon

George H. Taylor
Weather Matters column, Mid-valley Sunday, May 25, 2003

You probably already know that Oregon is really two states. West of the Cascades the chief characteristics are rain, clouds, lots of green, and people. East of the Cascades? We can talk about sun, temperature extremes, sagebrush, wide open spaces, lots of earth tones, few peopleand wind turbines!

Alternate energy sources are becoming more and more interesting and taking on a bigger place in the future of Oregon and the U.S. "Traditional" energy generation in our region has consisted primarily of fossil fuel operations (for example, natural gas electric generation) and hydropower. As population grows in the Northwest, demand for electricity and other power sources will continue to increase, forcing us to face the question: how should we meet this demand? Is it adequate to reduce demand through conservation? Should we increase traditional power sources? Turn to nuclear power? Or explore "alternate" sources?

Among most promising of the latter is wind energy. According to Phil Barbour of OSU, Oregon and Washington are leading the nation in new wind energy installations. Phil works with Stel Walker, who directs the Energy Resources Research Lab in the Mechanical Engineering Department here. They have worked in the wind energy field for a number of years, helping prospective "wind farmers" find the best places for new installations.

Phil told me that new projects are going in on a regular basis, with many more proposed. And for many of the small rural economies in central and eastern Oregon, these projects are increasingly popular. Farmers and ranchers in favorable wind energy areas are paid an annual fee for each wind turbine installed - typically $2000-4000 per turbine. And the farming and ranching can continue unabated.

Each turbine units consists of a tower several hundred feet high with a large propeller, usually with three blades, that drives a generator when it rotates. Each turbine can generate about one megawatt (MW) of electricity, enough to power about 300 average homes, but as the technology gets more sophisticated, the power output has gone up. New units in the 3-4 MW range are becoming available.

According to the Renewable Northwest Project (www.rnp.org), the Pacific Northwest has the potential to generate 133,000 average megawatts or more of electricity from wind power. The majority of the region's wind resources are in Montana, but some of the best sites are also in Idaho, Oregon and Washington. Montana alone has enough winds resources to supply 15 percent of U.S. electricity demand; Oregon and Idaho could meet all of their power needs with wind, and Washington could use wind power for about 3 million homes.

There have been some drawbacks to wind energy. The visual aesthetics have been a big issue (a 200 foot wind turbine is VERY visible!). And in areas such as California's Altamont Pass east of San Francisco a large number of eagles, hawks, and other avian species have been killed as they flew through the rapidly-rotating blades. Phil Barbour told me that by more careful siting (moving the units away from canyons) and lower rotational speed, the danger to birds has diminished. In fact, Phil said, the Audobon Society ahs been a big supporter of wind energy.

The most promising areas in Oregon for wind energy are the Columbia Gorge and the areas south of the Columbia in north central Oregon near Pendleton. Here in western Oregon, with the exception of the coast, there usually isn't enough wind for commercial generation. And there has been opposition to wind turbines in areas like Tillamook because of the visual impacts of wind energy. Meanwhile, our brothers and sisters on the east side say "Send those wind turbines over here. We think they're beautiful!" And so a new era of farming dawns above the wheat fields in eastern Oregon

Questions from readers

Q. Are we going to have water shortages this summer?

A. Depends on what you mean by "we." Locally, no. Western Oregon, no. Despite what remains a subpar snowpack, we've had a wet enough winter that no problems are anticipated west of the Cascades.

But then there's the Klamath. You'll recall the "water wars" 2 years ago, when a number of Klamath farmers were denied irrigation water. A low snowpack (59 percent of average at present) means that water supply will probably be rather short this summer, since a large portion of summer water comes from snow melt. According to U.S. Water News Online,

"The federal government has begun taking applications for $4 million in payments to Klamath Reclamation Project farmers who let their fields go dry and sell groundwater to provide higher springtime flows for salmon in the Klamath River.

"The payments are being made from a water bank started this year by the U.S. Bureau of Reclamation to meet its obligations to fish under the Endangered Species Act.

"The agency is hoping it will not have to repeat the 2001 irrigation shutoff that brought upheaval to the basin.

"The 55,000 acre feet of water purchased from farmers within the project will likely be used to augment springtime flows down the Klamath River, where coho salmon are listed as a threatened species, said Dave Sabo, Klamath area manager for the bureau.

"The bureau hopes to save about 30,000 acre feet of water by paying farmers not to irrigate up to 12,000 acres of land throughout the irrigation project that covers 235,000 acres straddling the Oregon-California border. It also hopes to buy about 25,000 acre feet of water from private wells."

Q. Are we going to have a bad fire year this year?

It's hard to say. Precipitation is only one factor affecting fire danger. The biggest variable is the occurrence of dry lightning storms. Two years ago, after one of the driest years in history in our area, we had a very benign fire year. Last year, following a near-normal winter, we had one of the worst fire years on record. Why? Not much dry lightning in 2001, and a LOT in 2002.

Oregon Climate Service

George H. Taylor, Oregon State Climatologist

Wayne P. Gibson, Programmer/GIS mngr.

Mandy Matzke, Research Assistant/Manager of Data Services

Melanie Mitchell, Undergraduate Assistant

Derek Gilbert, Undergraduate Assistant

Wolf Read, Undergraduate Assistant

Emily Gibson, Student Assistant

Oregon Climate Service, Strand 316,                                 Phone: (541) 737-5705  
Oregon State University                                                      Fax: (541) 737-5710   
Corvallis, Oregon  97331                                                     E-mail: oregon@oce.orst.edu   
                                                                             Web: http://www.ocs.oregonstate.edu