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00-:G71 FOR THE SECOND MONTH IN A ROW. DRY WEATHI:.R PATTERNS UVEH. ALMUST ALL OF Tl-U:. WESTERN U.S. HAVE CAUSED DECREASES FOR NEARLY ALL STREAMFLUW VULUME FORECASTS. WATeR SUPPLIES IN THb GREAT, COLORADO, ARKANSAS, AND RIO GRANDE BASINS ARE STILL EXPECTm TO BE AllOVE AVERAGE BECAUSE OF Hu\VY. EARLY SEASON PRECIPITATIUN WHICH SATUI{ATED MOUNTAIN SOILS AND BUILT UP HEAVY S~OWPACKS. HOST OTHER WATERSHEDS ARE EXPI:.CTED TO PRODUCE NORMAL TO BELOW NORMAL RUNOFF. WITH THE EXCEPTION OF THE UPPER MISSOURI AND UPPER COLUMBIA BASINS IN MONTANA AND THE CENTRAL ARIZONA BASINS, WkERL PRECIPITATION OVER THE LAST TWO MONTHS HAS BEEN ALMOST NONEXISTENT. 1984 Snowmelt Sea80n all of March 1 General Outlook Even though some streams in the West are expected to produce above normal runoff volumes, nearly all forecasts are lower than the February I values. Two straight montha of generally below normal precipitation has reduced potentially disastrous streamflow volumes to the normal to above normal range, and below average streamflow volumes to the much below normal range. Some areas in Arizona are expected to produce less than 20 percent of average runoff volume. As previously mentioned, February was a repeat of January, with below normal precipitation over mOBt of the West. Parts of northwestern Hontana and Ariz.ona have gone two months without measurable precipitation. If this trend continues, there could be severe water shortages for some uses in these areas. Areas of above normal precipitation were lDainly limited to the eastern half of the Great Basin, southwest Oregon. the Platte River Basin, and the Upper Arkansas Basin. Consistent with the below normal precipitation, snowfall was below normal over almost the entire West in February. This has caused reductions. sometimes significant, in the average basin snoW' water content In relation to normal for most watersheds. The normally heavy snowfall areas in northwest Hontana would require 200 to 300 inches of snowfall durlng March in order to reach average April 1 water content levels, while in Arizona it is very difficult to find any snow to measure. Spring and sUllllDer runoff is still forecast to be above normal in the Great, Colorado, Arkansas, and Kia Grande Basins. Elsewhere, streamflows are expected to be slightlY below to much below normal. The tHssouri River is expected to yield 6Y percent of average at FQrt Peck, Hontana.. The Columbia River 18 expected to yield H8 percent of its average and the Snake River 91 percent. The Colorado River is forecast to produce 151 percent of its average flow into Lake Powell, with the Rio Grande and the Arkansas both near 160 percent of normal. The yield from the Great Basin streams is expected to vary from near normal to over 60U percent of average in the Sevier drainage. Reservoir storage continues to be a throughout the West, with all states at reservoir storage levels for March l. augmentation from these reservoirs will needed throughout the West this year. bright spot above normal Srreamflow be very much Basin by Basin Summary SAN JOAQUIN. SACRAMENTO AND NORTH COASTAL BASINS The dry and mild weather pattern which became established over the west COBst during January continued through February. At many southern California stations, this January-February period 16 the driest ever recorded. However, in the Sierra Nevada. which provides the bulk of California's water supply, the precipitation is much closer to normal. As a consequence, the annual runoff is still expected to be above normal. Precipitation for the month of February was only above normal on the extreme north coast, 120 percent of average. Precipitation throughout the Sierra Nevada ranged from 55 percent of average on the northern and southern ends to 90 percent of average in the Central Sierra. Because of the heavy precipitation in the faU months, the seasonal precipitation totals are mostly above normal, ranging from near normal in the Kearn River Basin to ISO percent of normal in the American River Basin. Forecast water streamflow volumes have remained the same or dropped only slighly since last month and are still above normal. COLUMBIA BASIN The 'oIater Bupply outlook for the Co1.umbia River and Pacific coastal basins calls for slightly below normal runoff volumes. Lighter than normal precipitation during February resulted in volume forecast decreases that averaged roughly 5 percent basin wide. Expected runoff from the Canadian portion remains slightly below normal while the Clark Fork. Flathead. and Pend Oreille Basins fell into the well below-normal range. The volume forecast for the Snake River Basin calls for slightly below-normal runoff. Above-average runoff is forecast for basins in southeastern Oregon and southwestern Idaho. Precipitation during February was well below normal over the bulk of the Columbia Basin. West-central Oregon received the heaviest rain due primarily to a sIngle storm that dropped 4.51 inches at Eugene, Oregon. The Columbia above Grand Coulee. WashIngton, received 52 percent of normal; the Snake River Basin above lee Harbor received 97 percent of normal; and the ColumbIa above The Dalles received 79 percent of normal February precipitation. Snowfall continued below normal for the Columbia Basin during February. Storms durIng the last two weeks of the month brought significant snow into the Oregon and Washington Cascades increasing the snowpack to slightly below normal. The main stem tributary basins of the Columbia in Canada continue to report below normal snowpscka. Some western Montana and northern Idaho anowpacks are 3D to 40 percent of normal. Southern Idaho has fared much better where southern Snake tributaries are reporting snowpacks well above normal. Central Oregon anowpacks are about normal for March 1. The January-July forecast for the Columbia River at The Dailes, Oregon, calls for 97.6 million acre-feet or 92 percent of the 1961-1980 average. At Grand Coulee, Washington, the January-July Columbia River flow is forecasr to be 57.8 miUion acre-feet or 89 percent of normal. The total contribution from the Snake River Basin. as measured at Lower Granite project, is forecast be be 32.2 rnilion acre-feet or 98 percent of normal for the January-September period. Reservoir storage is excellent. was above normal in all areas and meet summer water supply needs. Storage as of Harch 1 should be adequate to GREAT BASIN 1 The water supply outlook for the Great Basin is for above to much above normal runoff with most forecasts ranging from 110 to It,5 percent. Host forecasts changed only slightly from those issued last month, however, heavy fall precipitation and saturated Boil conditions