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U lJ l I " I Snowpacks in ~outhern Utah have also been depleted. May I snowpacks in northern Utah are about 15 percent of average and limited to the highest elevations. In southern Utah. snowpacks are 40 to 60 percent of average, again at the higher elevations. Nevada's "best" snowpack is in the Walker River Basin. which reported 27 percent of aver.:Jge on May I. Six of the m.~or has ins in Nevada reported 0 per. cent of average snowpacks. Streamflow. April-July volume fore- casts as of May I range from 20 to 45 percent of the 1961-1990 average in northern Utah and 40 10 I ()() percent in southern Utah. April-July tlow volumes along the east slope of Lhe Sierra are expected to be about 25 percent of aver- age, but in the Humbolut River Basin only 12 percent of average. Many streams throughout Lhe north- ern portion of the Great Basin have peaked during the last two months. The remainder of the streams are expected to peak shortly. April streamflow volumes in Utah varied widely. ranging from 30 to 140 percent of average. TIle highest flows have been in southern portion of the state and in the headwaters of the northern basins because of an early snowmelt. Reservoir storage at the end of April ranged from 40 to 90 percent of capaci- ty i.1CroSS Utah, with a statewide average near 60 percent. Storage at northern Utah reservoirs changed very little from figures reponed last month. Reservoirs in southern Ulah show a decrease of 5 to 10 percent. Reservoir storage in Ne- vada was well below average 011 the last day of April. Statewide, storage is 10 percent of ci\pacity and 14 percent of average. Columbia Basin Most of the Columbin Basin received above average precipitation in April. but the water supply outlook remains bleak. Only the Upper Columbia in Canada showed slight volume increases. Record low nows are forecast on sever- al sub-basins in southern Idaho, on the lower main-~lem of the Snake and in several Oregon sub~basins. Abnonnally warm temperatures have caused an ex- tremely early melt. Lute seasun water supply is expected to be severely hmited. Precipitation. April precipitation was above average throughout most of the Columbia Basin. The heaviest precipi- tation fell in western Oregon. where amounts approached 200 percent of ~verage. The remaining sub-basins were in the 120 to 150 percem range, with the exception of the middle and upper Snake. upper John Day and the Great Basin in Oregon where precipita- tion ranged from 60 to 100 percent. October-April precipitatiun for the Col umbia Ri ver. above both Grand Coulee and The Dalles was 81 percent. The Snake River at Lower Granlte re- ported 76 percent uf average for the same period. SIIowpack cuntinued to decline in April. with the percentl)f average drop- ping 24 percent. Major contributing factors to the decline were large snow- pack losses in the Upper Columbia sub- basins. The Spokane and Salmon basins both dropped 22 percent in April, while the Kootenai .md Yakim<l basins dropped 18 percent. The Pend Oreille Basin dropped II percent and the Snake head- waters dropped 27 percent. nlese ba- sins combine to account for 49 percent of the Columbia Basin water supply. Streamflow forecasts range from near average in the Upper Columbia in Can- ada to less than 10 percent in the south- ern sub-basins. Foreca~lS in the Cascades, Flathead, and Kootenai are 60 10 80 per- cent of average, while southern sub-basin forecasts are 20 to 50 percent. With the warm temperatures., residual flow will be extremely low. falling into the 20 to 50 pen'em range. The JanuaJy-July forecast for the Columbia River at Grand Coulee is. 49.7 million acre-feet IMAF). or 79 percent of average, up I percent from April l. llle foreca"it for the Snake River at LQwer Granite for the January-July period is 9.8 MAF, or 45 percent of average. The January-July forecast at 'TIle Dalles, lIm.:hanged from last month, is 7\.2 MAF. or 67 percent of average. By comparison. the 1991 runoff was 107 million acre-feeL Reservoir storage on May I continues to be very poor in the southern part of the Columbia Basin. where many reser- voirs are at less than 20 percent of aver- ag.e contents. This lack of slOrage has 3 severely impacted inigation supply in these arcas. On the good side. reser. voirs in Wa~hington. northern Idaho and western Montana have near to slightly below average contents which will pro. vide adequate irrigation waters in these areas. San Joaquin, Sacramento and North Coastal Basins Water year runoff in 19Y2 is expected to be about 50 percent of average. similar to last year. This is the sixth consecu- tive year of much below average runoff. Precipitation. April precipitation was 125 percent of average in the Trinlty and Upper Sacramento river basins, but decreased rapidly to 70 percent of aver- age in the McCloud and Pit river drain- ages into Lake Shasta and also in the Feather and Yuba river basins. The American and Mokelumne liver basins received only 25 percent of the monthly average. Southward along the Sierra. April precipitation was almost non- existent at 7 percem of average in the San Joaquin and Tulare Lake drainage basins. Seasonal precipitatiun since October I is about 85 percent of average state- wide. The central valleys and the cen- tral and southern coastal areas received above average precipitation. Amounts in the major Sierra watersheds were generally 70 percent of the seasonal average. Sllowpack. April temperatures were near record high levels. melting the 111cager Sierra mowpack early. Only the highest elevations of the Sierra had snow cover on May I. The May I snow- pack water content was only 25 percent of average cum pared 10 65 percent last year. Reservoir. Total reservoir storage in California on the first of May was 20.2 million acre-feet, or 72 percent of aver. age. This is about 2 million acre-feet more than last year. However, because of the wann spring most of the snow- pi.tck has already melted and mountain stream runoff should recede rapidly. As a result. the current reservoir storage advantage is likely to fade during the nex! two monLhs to levels similar to last year.