May 6, 2021 Water Supply Forecast Discussion — Colorado Basin River Forecast Center #ColoradoRiver #COriver #aridification

Click here to read the discussion from the Colorado Basin River Forecast Center. Here’s an excerpt:

The Colorado Basin River Forecast Center (CBRFC) geographic forecast area includes the Upper Colorado River Basin, Lower Colorado River Basin, and Eastern Great Basin.

Water Supply Forecast Summary

Early May water supply volume forecasts are below to much below normal throughout the Colorado River Basin and Great Basin. Upper Colorado River Basin water supply forecasts range between 15-75% of the 1981-2010 historical April-July average. Great Basin water supply forecasts are 10-70% of average. Water supply guidance as a percent of average decreased by 10-20% across the majority of the Upper Colorado River Basin and decreased by 5-15% across the majority of the Great Basin over the past month. Many April-July volume forecasts fall in the bottom (driest) five on record. Water supply forecast ranges (percent of normal) by basin are listed below.

April average temperatures were slightly below normal across the north and slightly above normal across the south. April precipitation was mostly below to well below normal across the Upper Colorado Basin and Great Basin. Several SNOTELs in the San Juan, Gunnison, and Yampa River Basins were below the 10th percentile for April precipitation. Below normal soil moisture and snowpack conditions in addition to below average April precipitation and relatively mild (near normal) April temperatures across the Upper Colorado River Basin and Great Basin lead to mostly below normal and in some cases record low observed April flows (unregulated streamflow volumes) across the region. A number of streamflow sites had record low April flows with many locations falling in the bottom five of their period of record.

Snow water equivalent (SWE) at the majority of SNOTEL stations across the region peaked between 70-85% of the normal peak SWE. Early May SWE conditions are below to much below normal (median) throughout the CBRFC forecast area. Upper Colorado River Basin SWE conditions generally range between 50-75% of the 1981-2010 historical median and Great Basin SWE generally ranges between 30-60% of normal.

April-July unregulated inflow forecasts for some of the major reservoirs in the Upper Colorado River Basin include Fontenelle 380 KAF (52% of average), Flaming Gorge 450 KAF (46%), Green Mountain 150 KAF (55%), Blue Mesa 340 KAF (50%), McPhee 81 KAF (27%), and Navajo 325 KAF (44%). The Lake Powell inflow forecast is 2.0 MAF (28% of average), a 17% decrease from April.

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