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GREAT BASIN The water supply outlook for the Great 8asin 1s for much above normal runoff throughout most of the basin, ranging from 81 percent on the Virgin River in Southern Utah to tHO percent for the local inflow on the Lower Sevier River at Gunnison. The Humboldt River Hasin Is an area of major concern for spring runoff with expected Apri I-Ju 1 y volume to be over JUll pe rcell t . Hos t 5 t reams are forecast between 125 to 2L5 percent of average. Forecasts increased 15-:'w percent from those issued last month. April precipitation was gent;>rally much above average basin wine, but the heaviest arl'3S were the Beaver <lnd Sevier Hasins 1n south central Utah and the Humboldt Basin in Nev",da. The only dry portion of the basin during April l.Ias o....er the Upper Sevier, Virgin, and eaDt slope Sierra basins. Seasonal precipitation, Uctober through April, was generally 120 to 15U percent o....er most of the basin and has exceeded previous observations o....er the Inst 5U years at se....eral locations. April snows pUDhed some snow courset; to record amounts for May I on several drainages, including the Humbuldt, Utah Lake, LOI.I~r S~vier, San Rafael, and Oquirrh Hountains. However, a dry pattern persisted over southern Utah, which was below normal. Some average basin snowjJacks include: Be.lr River - 142 percent. Logan _ 135 percent, LJgden - i4l:l percent, Weber - 144 percent, Jordan - 176 percent, Pro....o - 152 percent, Beaver - 177 percent, Upper Sevier - 131 percent, Lower Sevier - 226 percent, and Humboldt - 2!H percent. Obser....ed streamflow continues to reflect the saturated soil conditions and high ground water flow. The se....en index stations measured by the USGS in Utah averaged 149 percent for April and since October I, 19l:lJ, have averaged 162 percent. The combined contents of '1.4 reservoIrs in Utah is 3.7 million acre-feet, 123 percent of average and 91 percent of ~apdc[ty. Th[s is about the same stor6ge as last year at this time, but the Weber and Ogden drainages have been dral.ln dololO to nearly half of average. High inflows to both Utah Lake and the Great Salt Lake are likely to push Utah Lake to a higher level than last year and the Great Salt Lake to l.Iithin 3 feet of the record HI73 level of 421 L.6 feet. COLORADO BASIN A cool wet April pro....ided additional snowfall throughout most ot Colorado pushing water supply forecasts upward 15 to 20 percent over most of the basin with some areas experiencing increases of 25 to 40 percent. The snowmelt runoff will be more than adequate for irrigation needs with some headwater areas experiencing higher flows than li1st year and lower basin drainages flows similar to last year with some flooding likely. Streams most likely to experience problems include: Uncompdhgre, Dolores, San Miguel. Plateau Creek. Lower Gunnison mainstem and the Colorado maIns tern between Grand Junction and the Moab area. Streamflow forecasts range from 144 percent in the headwaters of the Gunnison river to 2U<J percent on the Colorado Ri....er at Cisco, Utah. The April-July inflow forecast to Lake Powell is 13.U million acre-feet, 174 percent of the 2U-year (1961-19!lU) average. Deficient flows are likely in Arizona with most streams producing less than 30 percent of normal runoff. April precipitation was hea....y .110ng the Continental Divide into southwest Wyoming, 140 to ll:lU percent. The central Gunnison Basin was near normal, but most of western Coiorado and eastern Utah was 1'1.0 to 150 percent of average. Arizona precipitation was 5U to I:HJ percent of normal. Seasonal precipitation, October thru April, ranges from less than tlO precent o....er northern Arizona to more than 150 percent in portions of western Colorado and southwest Wyoming. Several records or near seasonal records were recorded in western Coloradu. The mountain snowpack generally increased throughout the month with Hay snow sur....eys showing significant increases except at the lower elevation courses where snowmelt is occurring. Some average basin water contents include: Upper Color~do : 16~ percent, Up~er Gunnison 156 p~rcent. San Juan Basin 116 percent, Green above flaming Gorge - 93 percent, Duchesne - 12'1. percent, Yampa _ 141 percent and White drainage - 164 percent. May readings !'lhow that at 44 snow courses, new records were set mostly in Ul>per Colorado and Gunnison drainages. some dating back to the late 1931J '5. Runoff in Upper Colorado during A.pril was near normal [n the headwater areas but increased significantly in the lower basins with the onset of the low elevation snowmelt. Reservoir storage remains high with the combined storage of ten major reser....oirs above Lake Powell of 5.!l3 million acre-feet, 73 percent of capacity, 130 percent of average, and about 34U,OOU acre-feet lower than last year at this tIme. Storage in Lake Powell is 21.Ub million acr~-feet, l:l4 percent of capacity and about 1.7 million acre-feet less than last year at this time. Reservoir releases on the Colorado Ri....er below Lake Mead continue to increase to provide room for the snowmelt runoff anticipated. But flows i'lre not expected to reach the flood levels of lalit year between l'arker and the Hexican border unless adverse weather should occur dgain during Hay and June. RIO GRANDE BASIN The water supply outlook for the kio Grande Basin calls for good water supplies for the entire basin. Forecasts increased the expected amounts slightly fronl a month ago, along the mainstem, and now range from 110 to 150 percent of average. Higher percentages are predicted for tributaries flowing from the Sangre De Cristos mountains, including the Pecos River Basin, and range from 130 to near twice long-term averages. Above normal precipitlltion was reported for much of the basin during the month of April. Several wet storm systems resulted in nlany New Hexico stations receiving 2 to 3 times monthly normals with amounts as high as 5 times normal around Taos. In the Colorado portion of the basin. slightly above average amounts were reported but totals as high as twice normal were included. Seasonal totals since October I, 1'::ll:S3, increased and now range from near normal to around twice normal but isolated areas as 10101 as only 50 percent of normal. Above normal snowfall in the San Juan Mountains of Colorado increased sno-wpack amounts about 10 percent in that portion of the basin abo....e Del Norte. Basin average in Colorado is now 117 percent of average which is about 88 percent of last year at this time. In New l~exico, only a few snow courses were scheduled to be read and they averaged about 136 percent of normal. Reservoi r storage is well above normal throughout the basin. ARKANSAS BASIN The Arkansas Ri 'o'er Basin wate r supply au t look ca IlG for much abo....e normal runoff. Predicted streamflow volumes have increased 10 to 20 percent over April 1 forecast and now range from 145 to 175 percent of the 2a-year (1961-19l:S0) a....erage. Several lDoderate to strong storm systems during April produced abo....e normal precipit.ation over most of the basin with the majority of the basin recei....ing l'1.U to 150 percent of average, with some isolated areas in the north recei....ing below normal totals. Seasonal totals October through April now range from near normal in the northern valleys to around twice normal further south and east along the Sangre De Cristos mountains and the southeastern quarter of Colorado. May 1 snowpack increased from a month ago at many of the higher ele....ation snow courses and continued much above normal at all observing points including some maximums of record for this time of year. Overall, the