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001C7;l PRECIPITATION DURING JANUARY WAS MUCH BELOW NORMAL OVER NEARLY ALL THE WE;l:iTERN U.S. FOR MANY AREAS, THIS WILL HAVE BEEN THE DRIEST JANUARY OF THIS CENTURY. A5 A RESULT NEARLY ALL STREAMFLOW VOLUME FORECASTS HAVE BEEN DOWNGRADED FROM. JANUARY I AMOUNTS. HOWEVER WATER SUPPLIES ARE STILL EXPECTED TO BE ADEQUATE OVER HOST OF THE WEST, BECAUSE OF ULJNDANT FALL PRECIPITATION. WHICH IN IUl{N LIW TO VERY HIGh. EARLY SEASON SNOWPACKS. OF CONCERN ARE THE TRIBUTARIES EMANATING PROM THE MONtANA ROCKIES. WHICH ARE EXPECTED TO YIELD BELOW NORMAL STREAMFLOW VOLUMES LATER ThIS SPRING AND SUMMER. 1984 Snowmelt Seaeon a8 of February 1 General Outlook With' most of the West receiving below average precipitation during January, most torecasts indicate volume flows to be less thsn those forecaBt on January 1. In spite of the low rainfall. much above average streamflow is still expected from atreams heading in the Sierra Nevada, Wasatch, and Colorado Rocky Mountains. along with streams in the Great Basin. Streamflows will be normal in o!1l1 other areas, with the exception of the tributaries heading in the Montana Rock.ies and the central Arizona streams, which will be below to much below normal. Precipitation was much below normal over the western U.S. with a few exceptions. January 1984, over a large portion of the West. will go down as the driest or nearly the driest JSllUary this century. The only areas with above normal monthly precipitation were western Washington, the extreme northern portion of the Columbia Basin in Britiah Columbia, central Wyoming, and small portions in eastern Colorado and northeastern New Me~ico. Even January. tied the though precipitation was below average in several snow courses in western Colorado set or msximum of record for February I. Many other areas in the West have much above normal snoWpack accumulations, a9 well, as a result of the tremendous snow accumulations in December. Much below norlllal snowpscks exist in weatern Oregon, western Wo.shington. central and northern Idaho, central Arizona, all of western Montana, and nesrly all of the areas draining into the Missouri River. Spring and summer runoff is forecast to equal or exceed normal in nearly all of the West's major rivers. The Missouri River is the major exception and is expected to yield only 79 percent of average at Fort Peck. Montana. The Columbia River 18 expected to yield 94 percent of its sverage and the Snake River 101 percent. The Colorado River is forecast to produce 166 percent of its average flow into Lake Powell, the Rio Grande 174 percent, and the Arkansas 170 percent of normal. Nearly all of the Great Basin streams are expected to flow in excess of 130 percent, with sin percent expected for the Lower Sevier drainage. Sierra Nevada streams will produce slightly above normal on the west side and much above normal on the east side. Reservoir storage is still above average throughout the West. High inflows are likely to push all lakes in the Creat Basin to even higher water levels than last year. in fact. higher water levels than have been experienced in almost a century. Basin by Basin Summary SAN JOAQUIN, SACRAMENTO AND NORTH COASTAL BASINS After two lIIOnths of much above normal rainfall. a large high pressure system became anchored over the west c~ast, virtually ending all precipitation in California. January 1984 will go dO\m in the record books aa the driest or nearly the driest January this century. Precipitation for the month of January averaged 5 percent of normal throughout the state. Some locations in the Southern Sierra reported no precipitation for the month. However, due to large amounta of precipitation received in November and December the seasonal precipitation is still much above normal, averaging ISO percent of norlPSl in the Sierra. The extremely high water contents that existed on January 1 have sustained the snowpack in the Sierra. The water contents contributed during January are generally 10 percent of the normal January additions. Low elevation snowpacks are well below average overall. The maximum January contribution occurred at Jess Valley in the northeastern corner of California with 30 percent of its normal January increase. Upper San Joaquin aitea at Huntington 1..s.ke and Plorence Lake had no snow water content addition. Overall snowpack in the Sierra is near average. The annual water supply picture i9 still healthy. The water year streamflow volumes are expected to range from 115 - 120 percent of average in the Northern Sierra, 140 - 160 percent of average in the Central Sierra. and 135 - 145 percent of. average in the Southern Sierra. COLUMBIA BASIN The water supply outlook for the Columbia River and Pacific coaatal basins shows a significant drop in the projected runoff volume from the January 1 forecast. The drop in projected volumes resulted from extremely dry weather during the month of January. Overall the water aupply outlook for the basin falls into the near-normal to below-normal category. Precipitation during the 1DDnth of January was 'Well below-normal over the bulk of the basin. The Columbia above Grand Coulee. Washington received 76 percent of normal while the Snake River Basin above Ice Harbor received only 40 percent of normal. Precipitation for the Columbia Baain above The Dalles. Oregon was jU9t 63 percent of normal. With essentially dry weather during the month of January, percentages of snoa/pack fell substantially throughout the basin. In Canada. snoWp8cks in the Upper Columbia were near norlll8l to slightly below normal. In the Kootenay drainage and in much of Hontana and northern Idaho the snoa/pack decreased to less than 70 percent. The Salmon and Clearwater drainages reported in 80-90 percent. Snake River tributaries in southern Idaho remained above normal in the 120 to 190 percent bracket but showed significant decreases from the January I readings. Central Oregon snowpacks averaged about 140 percent of normal. Higher elevation measurement in thljl Oregon and Washington Cascades were slightly less normal and lower elevations reported lesa thsn 50 percent of normal. Near normal snoWpacks a/ere measured in the interior basins of northern Washington and southern Canada. The January-July forecaat for the Columbia River at The Dalles, Oregon calls for 103.0 million acre-feet or 97 percent of the 1961-1980 average. At Grand Coulee. Washington. the January-July Columbia River flow is forecast to be 60.0 million acre-feet or 93 percent of normal. The total contribution from the Snake River Basin. aa measured at Lower Granite Project, is forecast to be 60.0 million acre-feet or 93 percent of norlPSl. The total contribution from the Snake River Basin. as measured at LOa/er Granite project. is forecast to be 34.6 million acre-feet for the January-September period or 105 percent of normal. The forecasts for the Pacific ~oastal basins of Washington slipped into the 80 to 90 percent of norlllSl bracket. The April-September forecast for the Willametle River at Salem fell to 92 percent of normal.