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Despite Higher Precipitation Lake Mead and Powell Not Expected to Recover From Drought

Drought Early warning System, Summary Feb. 26,2019.

News from The National Oceanic and Atmospheric Administration’s (NOAA) National Integrated Drought Information System (NIDIS) , February 26, 2019

Colorado River System
(Wikipedia commons)

Yesterday, the NIDIS reported that The Upper Colorado River Basin (UCRB) has reached the point where days begin to last longer, and temperatures start slowly upward. That said, winter 2019 will not be going anywhere without a fight.

Steam-flow and deep soil moisture continue to be low in most areas of the Inter-mountain West (IMW).

Storage in reservoirs in the northern half of the IMW are generally in good. However, conditions worsen further south. Notably, Lake Powell, Lake Mead, Navajo Reservoir, and Blue Mesa Reservoirs are all large, heavily-used, bodies of water showing deficits. It would be possible to fill Blue Mesa and Navajo Reservoir with a much above average snow year, but unlikely. Lake Powell and Lake Mead will not recover their multi-year deficits in any individual year.

The entire western United States saw below average temperatures over the past week. The Inter-mountain West was from five degrees below normal in the central Colorado Rockies to 25 degrees below normal east of the Bighorns in Wyoming.

Some parts of the Inter-mountain West (IMW) received major snowfalls. Payson, AZ recorded 31.8″ of snow in 48 hours. Totals in the Colorado San Juans were impressive. Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) stations in the Durango area recorded as much as 23″ in 24 hours. The Wolf Creek Ski area recorded 86″ of snowfall in a seven-day period. That’s an average of over one foot/day. While these are extreme examples, Pacific Moisture did grace a large portion of the region.

Following the big snows, long-term  Standardized Precipitation Index (SPI)  are improved but highly variable. Tailoring the drought map around individual stations is exhausting, and probably unnecessary. Regional snow-pack numbers tell a more consistent story. Snow-pack is now above average for nearly the entirety of the Inter-mountain West. The main exception is southern New Mexico. Parts of southern Utah and Colorado have even eclipsed average seasonal peak values.

Numerical weather prediction models indicate that cooler and wetter than average conditions are likely to persist over much of the IMW over the next two weeks. Seasonal guidance suggests a tilt towards wetter conditions across the region, with equal chances of above and below normal temperatures this spring.

Recommendations:

Researchers for the Sangre de Cristos Mountains (UCRB) recommend that all remaining D3 be wiped from Colorado and Utah. The remaining D3 area had highly variable precipitation over the past week (0.25″-5.50″), and long-term SPIs tell a muddy story with a mix of D to D4 at the 12-month time scale. Regardless of the variability, much of this area conforms to the same narrative: Snow-pack is above average at a critical point in the season, which renders “extreme drought” a disingenuous appraisal. However, soils, stream-flows, and reservoirs are going to need continued greater than average winter precipitation to fully recharge.

Sangre de Cristos Mountain Range

They recommend that D2 be improved to D1 for southeast and central San Juan County in Utah, and for western and central Montezuma County in Colorado. These areas have seen well above average moisture since the start of the water year. Cortez has had 149% of normal precipitation for the water year to date. Blanding, UT has had 167%. The SNOTEL stations feeding into McPhee Reservoir are at about 80th percentile snowpack.

However, after further consideration, they are a bit uneasy about removing D2 in Durango. The La Plata County Airport station is still only at 49% of normal precipitation going back to the start of Water Year 2018. For reference, Cortez is at 80% of normal. The impacts of Durango’s large precipitation deficit may already be water under the bridge (or lack thereof) at this point, but we’ll wait and see for now.

It is recommended that D2 be improved to D1 for the eastern San Luis Valley. The San Luis Valley Airport in Alamosa has received 164% of normal precipitation for the water year to date, has a near zero 12-month SPI, and was much colder than average over January due in large part to persistent, deep snow-pack.

It is recommended that D1 be changed to D0 for southern Sweetwater County, and southeast Uinta County in WY, far western Moffat, Rio Blanco, Garfield, and Mesa Counties in CO, and in much of eastern and southern Utah. This broad area is now showing positive SPIs for all timescales from 12 months down to 30 days. Snow-pack is well above normal throughout eastern and southern Utah with only a few isolated exceptions.

It is recommended based on feedback from the Farm Service Agency (FSA)  in Utah that D2 in western Utah potentially be improved. This area is data sparse, and out of our wheelhouse, so no official recommendation from the Colorado Climate Center.

Eastern Colorado: It is recommended that remaining D2 be improved by one category where it remains in Elbert, Lincoln, and eastern El Paso Counties. This area is still on the dry side, but long-term deficits are now similar in scale to surrounding areas of D1.

NIDIS researchers continue to monitor some areas of below average winter precipitation and above average evaporation demands on the northern urban corridor and northeast plains.

About Author

Michael McGreer Mesquite, Nevada
Dr. Michael Manford McGreer is managing editor of Nevada-today.com and writes on issues that impact public policy.

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