GENERAL OUTLOOK

Beneficial rainfall and some new snow accumulations helped the water supply outlook slightly. The exception to this is on streams draining the Washington Cascades where forecasts decreased somewhat.

PRECIPITATION SUMMARY

COOLER THAN NORMAL IN APRIL, DRIER THAN NORMAL ACROSS SOUTHERN OREGON, NORTHERN WASHINGTON, AND SOUTHEAST IDAHO, AND NEAR OR ABOVE NORMAL PRECIPITATION ELSEWHERE ACROSS THE REGION IN APRIL

The split flow that has been bringing much drier than normal conditions to the Pacific Northwest during the winter finally broke down during April. With the lack of a persistent ridge of high pressure along the Pacific Northwest coast, storm systems over the Gulf of Alaska and Eastern Pacific Ocean were able to track into the Pacific Northwest on a more frequent basis and with greater intensity. This pushed precipitation totals to above normal levels across the Owyhee, Salmon, Kootenai, Flathead, and Middle Columbia River Basins.

Pacific Northwest mean temperatures departed -1.1 degrees from normal relative to 1961-1990 normals (31 stations). Mean temperature departures range from -3.2 to 2.3 degrees.

There were 5 new high temperature records established in April. They include: 80 at Pendleton(Downtown) on the 16th, 69 at Astoria, 77 at Klamath Falls, and 82 at Portland on the 25th, and 91 at Havre on the 28th.

There were 25 new low temperature records established in April. They are listed below according to the date they occurred:

April 3rd, -1 at Butte, 29(tie) at Pendleton, and 30(tie) at Eugene
April 4th, 13 at Kalispell, 15 at Redmond, 28 at Pendleton, and 30(tie) at Eugene
April 5th, 14 at Redmond and 30(tie) at Eugene
April 7th, 7 at Butte
April 8th, 22(tie) at Yakima
April 9th, 7 at Austin, 10 at Redmond, 12 at Prineville, 15 at Meacham, 17 at Klamath Falls, 20(tie) at Long Creek, 21 at Madras, 24(tie) at La Grande, 24 at Pendleton Exp. Station, 28 at Pendleton, and 32 at The Dalles
April 10th, 10(tie) at Butte
April 14th, 31(tie) at Astoria
April 29th, 18 at Burns

There were 9 new daily precipitation records established in April. They are listed below according to the date they occurred.

April 3rd, .12 inches at Yakima
April 6th, .51 inches at Portland
April 7th, .63 inches at Missoula
April 8th, .43 inches at Kalispell
April 10th, .17 inches at Yakima and .44 inches at Pendleton April 20th, .51 inches at Butte
April 30th, .57 inches at Salem and .74 inches at Astoria

For APRIL, PRECIPITATION is: 120 percent of normal (1961-1990) at COLUMBIA ABOVE COULEE, 106 percent of normal at THE SNAKE RIVER

ABOVE ICE HARBOR, and 117 percent at COLUMBIA ABOVE THE DALLES.

For the WATER SUPPLY SEASON, PRECIPITATION is: 65 percent of normal (1961-1990) at COLUMBIA ABOVE COULEE, 76 percent of normal at THE SNAKE RIVER ABOVE ICE HARBOR, and 67 percent at COLUMBIA ABOVE THE DALLES.

SNOW SUMMARY

Some increases in snow water equivalent percentages were observed in British Columbia, Montana and Northern Idaho. In contrast, snow percentages dropped sharply on the Snake river plain basins, on all Eastern Oregon tributaries and in Southwest Oregon. Snow percentages range from 75 percent on the Flathead River in Montana to 30 percent in Eastern and Southwest Oregon.

RUNOFF

Some rainfall and snowmelt runoff increased observed runoff in most areas of the basin. However, runoff still ranges from 30 to 60 percent in most areas. The exception is the upper Columbia in Canada, the upper Yakima river and most of the upper Snake river where April runoff ranged from 70 to 90 percent. Increases in volume forecasts occurred on most basins. Percentage change from April 1st was fairly small at 2 to 5 percent. The May 1st January - July forecast for the Columbia river at The Dalles is 56.5 million acre-feet (MAF) or 53 percent. This is an increase of 1 percent from April 1st. This compares to a runoff of 98.0 MAF last year.