Overview

April was warm and dry, but generally not quite as much as March was. Nonetheless, the 2-month combination was an unusually warm and dry period. Oddly, a year ago we experienced one of the coolest and wettest March-April combinations in Oregon’s history. 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. Figure 1 shows the percentage of seasonal precipitation statewide.

Basin Summary

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

	Precipitation			Snow	Stream Flow		SWSI
BASIN	(1)	(2)	(3)	(4)	(5)	(6)	(7)
OWYHEE	40	69	96	45	53	77	-0.6
MALHEUR	70	93	96	52	7	37	0.0
GRAND RONDE, POWDER, BURNT	78	97	96	62	88	80	-0.6
UMATILLA, WALLA WALLA, WILLOW	97	102	99	58	104	98	1.0
UPPER JOHN DAY	100	94	94	29	83	86	0.8
UPPER DESCHUTES, CROOKED	97	103	91	82	81	59	0.4
LOWER DESCHUTES, HOOD RIVER	49	95	88	72	85	73	-0.5
WILLAMETTE	70	92	89	77	71	84	0.4
ROGUE, UMPQUA	77	98	94	92	54	82	0.4
KLAMATH	51	97	92	82	62	68	-1.3
LAKE COUNTY, GOOSE LAKE	61	80	87	47	74	66	0.2
HARNEY	79	75	98	49	68	78	0.1
NORTH COAST	64	87	n.a	n.a	59	79	-0.4
SOUTH COAST	91	100	n.a	n.a.	109	89	-0.9

n.a. Not available
(1) Percent of normal April 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 April 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 May-July appear below. Temperatures for western Oregon are likely to be above normal, with equal chances of above or below normal east of the Cascades. Precipitation probabilities are not significantly different from average conditions. CPC also says:
“ENSO-neutral conditions are expected to continue during the next three months. For the Pacific basin as a whole, oceanic and atmospheric conditions continue to reflect the neutral phase of the ENSO cycle. However, sea surface temperature (SST) anomalies in the equatorial Pacific increased during April 2004 in the Niño 3.4 and 4 regions, and decreased in the eastern Pacific, as the equatorial cold tongue strengthened. By the end of the month, positive SST anomalies greater than +0.5°C (~1°F) were observed in the region between Indonesia and 180°W, and negative anomalies (less than -2°C in some places) were observed between 120°W and the South American coast.” In other words, “La Niña-like” conditions are showing up now, but CPC doesn’t expect them to continue.

Oregon Climate Service predicts near-normal temperatures and precipitation for May. For the three-month period May-July we predict normal temperatures and below-normal precipitation.

Oregon Water Supply Outlook Report as of May 1, 2004, from by USDA-NRCS
For the second consecutive month, conditions in Oregon can be summarized as dry and warm. The well above average snowpack that was measured on the first of March has largely melted. As of May 1, the snowpack in the mountains of Oregon was between 96 percent of average in the Rogue and Umpqua Basins and 40 percent of average in Lake County. This can be compared to March 1 when the snowpacks were between 153 and 109 percent of average. Precipitation for April was below average in all basins, ranging from 90 percent of average in the Owyhee/ Malheur Basins to 45 percent of average in those basins surrounding Mt. Hood. Since the start of the water year the total amount of precipitation has ranged from 97 percent of average in the Upper John Day Basin to 81 percent of average in Lake County. Water stored in the 27 major irrigation reservoirs in the state increased from last month. As of April 30, there were 2,099,500
acre feet of water stored, representing 81 percent of average and 67 percent of the capacity. Observed stream flows have generally decreased since last month. The streamflow forecasts for the remaining spring and summer months are between 95 percent of average on Tumalo Creek and 21 percent of average on Silver Creek near Silver Lake. Careful water management of limited supplies will be necessary in many areas of the state to meet the water demand, but some users can expect water shortages this season.

SNOWPACK

As of May 1, the snowpack in the mountains of Oregon was between 96 percent of average in the Rogue and Umpqua Basins and 40 percent of average in the Lake County area. At some locations even these values are misleading. Much of the snow in all the basins of Oregon has melted, in some instances anywhere from one to one and a half months early depending on location and elevation. The snow remaining is generally at the higher elevations and doesn?t represent a large amount of snow available for runoff. The impact of the below average precipitation and the above average temperatures on the mountain snowpack since March 1, has produced a decline of substantial proportions. On March 1, the snowpack was between 153 percent of average in the Harney basin and 109 percent of average in northeast Oregon. Generally, the maximum accumulation of snow occurs between April 1 and April 15, depending on the elevation. Even the deepest measured snowpacks began melting in March this season.

RESERVOIRS

Most reservoirs in the state continued to store water during April, but there were a few where drafting of the stored water has already been necessary. The 27 major irrigation reservoirs in the state had 2,099,500 acre-feet of water stored at the end of April, representing 81 percent of average and 67 percent of the capacity. This is an increase of 74,100 acre-feet since last month. Many reservoirs will not fill this season. Last year the same 27 reservoirs had 1,866,700 acre-feet of water, or 70 percent of average and 57 percent of the capacity.

STREAMFLOW

Observed streamflow in April were generally lower than last month. Many streams have already experienced the peak of the runoff derived from snowmelt and are receding. The streamflow forecasts for the remaining spring and summer months are between 95 percent of average on Tumalo Creek and 21 percent of average on Silver Creek near Silver Lake. Water uses in many locations of the state will experience shortages this season. In other areas, careful water management will be necessary to make the supplies last. The following table summarizes the forecasts for selected streams in the state.

Hotly Disputed UW Analysis Makes a Case for Warming
The Seattle Times, 6 May 2004

http://seattletimes.nwsource.com/html/localnews/2001921103_globalwarm06m.html

By Sandi Doughton Seattle Times staff reporter

Seattle scientists say the lower atmosphere is heating up, a discovery that, if true, would overturn one of the main arguments against global warming. But even before the results were published in today's issue of the journal Nature, critics launched into a scholarly version of trash-talking, claiming the University of Washington group is flat wrong.

"It's going to be a very healthy scientific debate," predicted Mike Wallace, a UW climate-change expert who was not involved in the research. "It will take a while to sit down and look at these arguments dispassionately." Qiang Fu, the lead scientist on the new analysis, said he expected controversy because the topic is central to the debate over climate change and the role of development and air pollution. "This is a very important question," he said.

Ample evidence shows that temperatures at the planet's surface have risen more than one degree Fahrenheit over the past century, causing glaciers to melt and sea ice to thin. But until now, studies of the Earth's lower atmosphere - the part where weather occurs - have shown little or no temperature increase. Global-warming skeptics say that suggests human activity is not changing the climate significantly.

Fu and his colleagues re-examined temperature data collected from weather satellites between 1979 and 2001. The satellites measure temperature in both the lower and upper atmosphere. While a human-caused global warming would be expected to raise the temperature in the lower atmosphere, computer models have shown it would have the opposite effect in the upper layer called the stratosphere. And indeed, temperatures there have been dropping steeply over the past several decades. Because satellite measurements from the different layers overlap, Fu suspected the cooling in the stratosphere might be masking any temperature increase in the lower atmosphere.

Fu's team developed a statistical approach to subtract the stratosphere's influence and found the hunch was correct: Temperatures in the lower atmosphere rose about one-third degree per decade, slightly more than the increase seen at the planet's surface during the same time frame. "I believe this shows the satellite temperatures can no longer be used as evidence to claim that global warming is not happening in the atmosphere," Fu said. "I think this could convince not just scientists but the public as well."

Some fellow scientists were not only unconvinced but dismissive of the study. John Christy, director of the Earth System Science Center at the University of Alabama at Huntsville, has been analyzing the same satellite data since the early 1990s, finding no evidence of a significant temperature increase. He issued a rebuttal yesterday, saying the UW group went too far in subtracting the stratospheric cooling. "The method they used creates a false warming signal," said Christy, who believes that humans are changing the climate, but that the changes are modest and not likely to cause ecological disaster. "Most of the predictions are too alarmist," he said.

Fu deflected the criticism and predicted his team's new study will be the final answer to the long-standing puzzle about atmospheric warming. "I'm confident this will not be an issue anymore," he said.

As an independent observer, Wallace said he thinks that Fu's approach seems reasonable, but that the debate won't be settled until all the scientists involved have time to hash out the data and the methods. "I won't profess to claim the verdict is in yet," he said.

Sandi Doughton: 206-464-2491 or sdoughton@seattletimes.com
Copyright © 2004 The Seattle Times Company

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

Wolf Read, Undergraduate Assistant

Emily Gibson, Student Assistant

Cadee Hale, Publications Assistant

Kelsey Kuykendall, Undergraduate Assistant

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