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002192 1985 Snowmelt Season as of May 1 WARM AND DRY APRIL WEATHER OVER MUCH OF THE WEST STARTED HEAvY SNOWMELT WHICH SEVERLY DEPLETED SNOWPACKS, CAUSED HIGH STREAM FLOWS , AND LED TO DOWNWARD REVISIONS IN THE SEASONAL FORECASTS. STREAMS IN SOUTHERN COLORADO AND NEW MEXICO WILL PRODUCE MUCH AROVE NORMAL RUNOFF VOLUMES THIS SEASON. General Outlook April weather conditions contributed to further decrease streamflow forecasts over a large portion of the West. EXpected volumes are below to much below normal for the Missouri, Great, and California Basins. Also, portions of the Snake and Upper Columbia Basins will receive beIo.... normal runoff d.mounts. Conditions in the Colorado, Arkansas, and Rio Grande Raains were not so hleak, ho....evet". Wet April conditions will keep maar of these basins ahove average. especially so in the San Juan and Rio Grande dt"ainages. A very wann and dry Apri I weather pattern dominated much of the Western U.S. Califot"nia stations only reported 15 percent of nOTillal precipitation state-wide, with the Missouri, the Great. and much of the Columhia Basins showing similar re!!ults. On the other hand, the Colorado, Ar}(ansas, and Rio Crande Basin!! received above normal precipitation during April. The Rio Grande Bssin experienced the wettest April in 40 years. As previously mentioned, a very warm April has greatly depleted the snowpack throughout the West. The very rapid depletion of the snow caused high runoff in most western streams and rivers during April, with many peake probably occurring during the month. The only area with a much ahov(:: normal snowpack is in the high elevation portions of southern Colorado and northern New Mexico, where rapid melt~ng is just getting underway. The Rio Grande River is going bananas this year and i9 now expected to produce 195 percent of average seasonal runoff. This is in stark contrast with other major rivers in the West, where forecasts are either staying the same or decreasing. Percent yields from other major rivers are as follows: Snake-98, Missouri-82, Columbia- 96, Colorado-145, Arkansas-98, Green-88, North Platte-68, and South Platte-IOO. Reservoir storage is Weat. The way things users are going to have of stored water. good to excellent throughout the look in many states, the water to rely heavily on this ahundance Basin by Basin Summary SAN JOAQUIN, SACRAMENTO AND NORTH COASTAL BASINS Following a cool and damp March in much of California, April weather patterns reverted to the dry conditions which have prevailed most of the winter. Statewide precipit8ti.:m averaged ahout 15 percent of nomal. Only a few sit~s in the .state reported TIIore than an inch of precipitation. Mt. Sh.asta City and Red Bluff reported their second dnest April on l:"ecord. Several locations in the Southern Sierra and Southern Cal i fornia recDrded no rain dUTing the month. April had very warm temperatures throughout the state, with every reporting station in California recording ahove norm.,l temperatures for the month. Average temperature anomalies of 3 to 5 degrees were most c~mmon for the month. Record Apri I average temperatures were established at Bll.1e Canyon with 53.4 degrees (10.1 degrees ahove normal) and at Mt. Shasta City with 51.7 degrees (6.1 degcee9 ahove normal). The Blue Canyon Apri I average temperat.ur~ ....as higher than t.he nonr.al May average of 51.5 degrees. As a result of the warm weather, the runoff from the snowpack began earlier than usual giving higher than normal streamflows for the month. However, expected water year streamflow volumes have continued to decrease and are expected to average 63 percent of normal. COLUMBIA BASIN The water suppLy outlook for the Columhia River and Pacific coastal basins calls for near normal runoff volumes this season. The conditions of April hoosted forecast volumes in the Canadian portion of the hasin and lowered forecast volumes in the Snake River Basin. The forecast for the Columhia River at The Dalles remained essentially unchanged norma 1 vo I ume. Mos t forecast to produce volumes this season. frow last month and refl~cts a near has ins in the Cascade Range are normal to slightly ahove normal Warm, dry days persisted across the Pacific Norrh....est during April with significant cooling only between the 18 .snd 28. Monthly temperatures generally averaged 2 to 6 degrees ahove normal. Precipitation was helow normal over the hulk of the hasin. l.Iet areas were limited to the Northern Cascades of Waahington, the Upper Columbia, and the upper portion of the Kootenia Basin. Mountain index stat ions received 6 to 24 i.nches of new snoW' late in the month. Precipitation for the month of April was 114 percent of average for the Columhia lIasln above Grand Coulee, 57 percent of average for the Snake River Basin ahove Ice Harhor, and 83 percent of average for the Columbia Basin ahove The Dalles. By May I, very warIP spring weather and small precipitation amounts dramatically changed the snowpack in the Columhia Basin. Only small, high elevation areas in the Oregon Cascades were still reporting at above normal level~. The snowpsck in the rest of the Cascade range was r~port.ed to be near nor~al for May 1. Central and eastern Oregon snowpacks fell to helow or much below average foe May 1. From the Salmon and Clearwater Basins in Idaho to the southern boundary of the Snake River drainage, the snowpack also fell to below to much beloW' normal. The snowpack in the Upper Snake Drainage in WyolDing and the entire northern parr ion of the Columbia River Basin was reported at normal to slightly below normal levels for May 1. The January-July forecast for the Columbia River at The Dalles, Oregon, calls fa 98.6 million acre-feet or 92 percent of the 1961-1980 average. At Grand Coulee, Washington, the January-July Columhia river flow is forecast to he 57.0 million acre-feet or !:I8 percent of normal. The total contrihution of the Snake River Basin, as measured above Lower Granite Project is forecast to be 30.8 million acre-feet or 94 percent of normal for the January-September period.