May 11, 2020 (UT, WY, CO)
- A very dry April in Utah and southern Colorado caused an acceleration of snowmelt, a decrease in forecasted seasonal streamflow volumes and a major expansion of drought in southern and eastern Colorado. While Utah and southern Colorado precipitation was much below average, near-average precipitation and near- to below-average temperatures prevailed in northern Colorado and Wyoming. Snowpack conditions are generally below to much below average in Utah and southern Colorado, but near average in northern Colorado and Wyoming. Regional May 1 seasonal streamflow forecasts are generally below average, with a few basins forecasted to have near-average or much-below-average seasonal streamflow.
- April precipitation was below average throughout the region except for isolated areas in north-central Colorado, southwestern Utah and western Wyoming, where precipitation was 100-150% of normal. Large swaths of eastern Utah, southwestern and eastern Colorado experienced less than 25% of normal precipitation. Much of the Wasatch Front also received less than 25% of normal precipitation. Wyoming was relatively wetter than Colorado and Utah, but precipitation in much of the state was 50-100% of average.
- April temperatures were generally below average in northern and eastern portions of the region and slightly above average in southern and western portions of the region. Temperatures in much of Utah during April were slightly above average, while temperatures in Wyoming were below average. Slightly above-average April temperatures in Utah were driven by much-above-average temperatures (10-20°F) during the last week of the month; the first three weeks of April were slightly cooler than average. April temperatures in Colorado were a mix of above average in the southwestern portion of the state and slightly below average in northern and eastern Colorado.
- Snowpack conditions across the Intermountain West as of May 4th mainly fall into the below-normal and near-normal categories . Warm temperatures and below-average precipitation caused snowmelt to accelerate during April in much of Utah and southern Colorado. Snowpack in much of Utah and southern Colorado is 50–70% of normal. Northern Colorado and much of Wyoming have near-normal snowpack. The increase in melt of Intermountain snowpack over the last month was driven largely by below normal regional precipitation and exacerbated by very warm temperatures in Utah and southern Colorado during the last week of April.
- The NOAA CBRFC May 1st seasonal runoff forecasts for the Upper Colorado River Basin and the Great Basin are generally below average; near-average and much-below-average conditions are forecasted for a few sub-basins . Near-average seasonal runoffs (90-110%) are forecasted for the Upper Colorado, Upper Green, Virgin and Lower Bear River basins. Below-average seasonal runoff (70-90%) is forecasted for the mainstem of the Colorado, Lower Green and Upper Bear River basins and the Six Creeks basin. Much below-average season runoff (<70%) is forecasted for the Gunnison, San Juan, Sevier and Weber River basins. In general, forecasted runoff volumes have decreased by 10-25% in the Great Basin, largely due to very low April precipitation. The inflow to Lake Powell on the Colorado River is forecasted to be 4.65 million acre-feet (65% average), which is a significant decrease from the April 1st forecast of 5.6 million acre-feet. The NRCS May 1st seasonal runoff forecasts are generally similar to NOAA CBRFC forecasts in the Upper Colorado and Great Basins . East of the Continental Divide, seasonal streamflow forecasts are near average for the South Platte River basin and below average for Arkansas River basin.
- A significant worsening of drought conditions in Colorado was driven by extremely low April precipitation and slightly above-normal temperatures. Total coverage of drought (D0 – D2) in Colorado expanded slightly in April, from 68% to 76% . In southern and eastern Colorado, precipitation was only 25% of average with isolated areas receiving less than 5% of normal precipitation. D3 drought emerged in portions of southern and eastern Coorado during April. D2 drought in this region of Colorado also significantly expanded. Coverage of D2 and D3 drought in Colorado was only 3% of the state on March 28th, but expanded to over 40% of the state by May 5th. Total coverage of drought in Utah remained mostly unchanged during April despite low precipitation and warm temperatures. A small area of D2 drought emerged in central Utah during April. D0 drought in Wyoming expanded significantly in the north-central portion of the state and covers 17% of the state.
- Ocean temperatures in the tropical Pacific Ocean were approximately 0.5°C above normal and ENSO phase was neutral during April . Tropical Pacific Ocean sea surface temperatures continue to trend towards average . During late spring and summer, ENSO is most likely to remain neutral, but by fall there are equal chances of each ENSO phase . NOAA one-month precipitation and temperature outlooks show a tilt in the odds towards below-average precipitation and above-average temperatures for much of the region. The three-month outlook shows no tilt for precipitation and a strong tilt towards warmer-than-normal temperatures for the entire region .
- Significant weather event for April. Record cold temperatures and snow impacted the Front Range and elsewhere in Colorado from April 11-16. Temperatures on April 13th in Denver dropped to 15°F, breaking the 1933 record of 17°F. On the same morning, temperatures in Grand Junction fell to 19°F, also breaking a 1933 record for that date. The peach crop in western Colorado sustained severe damage from the deep freeze. Light snow fell throughout the Front Range during the cold wave, but heavy snow developed near the foothills in Boulder County where over 30” fell over the five-day period. By the end of the storm cycle, the 2019-2020 winter season had set the record for the snowiest winter in Boulder, CO, with 152.0”, eclipsing the record set in 1908-1909.
