GENERAL OUTLOOK

Below average monthly rainfall and a depleted snowpack produced a slight

drop in volumes in most areas.

Precipitation Summary

WARMER AND DRIER THAN NORMAL MAY

Early in the month, a series of frontal systems moved across the region and had their greatest impact across Washington, Northwest Oregon, Northern Idaho, and Southern British Columbia basins. Late in the month, drier than normal conditions dominated as the main storm track lifted north into Canada.

Pacific Northwest mean temperatures departed +2.0 degrees from normal relative to 1961-1990 normals (31 stations). Mean temperature departures ranges from -1.3 to 6.4 degrees.

There were many new high temperature records established in May. They include:

86(tie) at Burns on the 11th, 82(tie) at Butte, 90 at Great Falls, 92 at Helena, 92 at Pocatello, and 93 at Havre on the 12th, 89 at Helena and 92(tie) at Great Falls on the 13th, 96 at Medford on the 21st, 90 at Eugene, 93 at Salem, 95 at Portland, and 100(tie) at Medford on the 22nd, 87 at Kalispell, 89 at Burns, 89(tie) at Helena, 95 at Medford, and 95 at Boise on the 23rd,

88 at Pocatello, 88(tie) at Burns, 89(tie) at Kalispell, 93 at Helena, 96 at Havre, and 97 at Boise on the 24th, 91 at Pocatello on the 25th, and 93 at Portland and 100(tie) at Medford on the 31st.

There were several new low temperature records established in May. They include: 22 at Pocatello and 31(tie) at Eugene on the 2nd, 23 at Kalispell on the 3rd, 24 at Pocatello on the 4th, 22 at Kalispell on the 6th, 24(tie) at Kalispell on the 7th, 32 at Eugene on the 10th, 41(tie) at Portland on the 18th, 28 at Kalispell on the 20th, 26 at Pocatello and 30 at Great Falls on the 21st, 28(tie) at Burns on the 29th, and 26 at Kalispell on the 30th.

There were just 2 new daily precipitation records established in May. Both were recorded at Astoria, where 1.32 inches fell on the 14th and .76 inches fell on the 15th.

For MAY, PRECIPITATION is:

59 percent of normal (1961-1990) at COLUMBIA ABOVE COULEE

48 percent of normal at THE SNAKE RIVER ABOVE ICE HARBOR

AND 62 percent at COLUMBIA ABOVE THE DALLES.

For the WATER SUPPLY SEASON, PRECIPITATION is:

64 percent of normal (1961-1990) at COLUMBIA ABOVE COULEE

72 percent of normal at THE SNAKE RIVER ABOVE ICE HARBOR

66 percent at COLUMBIA ABOVE THE DALLES.

SNOW SUMMARY

On June 1st the snowpack is mostly depleted. Only the upper Columbia in Canada, the North Cascades in Washington and the Flathead River in Montana have any noteworthy snow remaining. Even in these areas the June 1st snow water equivalent percentages are less than 40 percent of average.

RUNOFF

A period of warm temperatures early in May produced moderate snowmelt runoff basinwide. May runoff ranged from 30 to 80 percent of average. Some Snake river tributaries had observed May runoff of less than 30 percent.

Streamflow forecasts decreased slightly in most areas. The June 1st forecast for the January-July period at The Dalles is 55.5 million acre-feet (MAF). This compares to a runoff of 98.0 MAF last year.