Colorado, central Utah get Snow, rest of Rockies lagging in moisture
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Although much of Colorado and central Utah have been blessed with winter moisture so far, however; the all-important snowpack in other parts of the Intermountain West is generally behind schedule for this time of year, according to presenters at the Intermountain West December Drought and Climate Outlook webinar Tuesday, Dec. 10. Colorado and interior Utah reaped the benefit of a couple of high-impact snowstorms, which upped the snowpack for those areas, and reduced drought pressure.
However, a large portion of the Rockies has been experiencing snow drought, especially in Wyoming, southwest Montana, Arizona and New Mexico. That is due to low precipitation causing drought pressure. That combined with above-average temperatures has produced a warm, dry start to the water year that started on Oct. 1. These factors resulted in extensive deficits in snow water equivalent or SWE across those areas in the Rocky Mountains. Although November finally brought a cool stretch of temperatures, the fall season was one of the hottest fall seasons on record for the region.
“The winter months are not typically when drought impacts are felt, however, the conditions occurring at the end of fall and throughout the winter snow accumulation season are critically important for next year’s drought impacts. As of right now, there are signs of potentially re-emergence of widespread drought impacts, as regional snowpacks are behind schedule, so soil moisture deficits throughout the region lower the expectation for an efficient spring runoff,” said Jon Meyer, Ph.D., assistant state climatologist, Utah Climate Center at Utah State University, Department of Plants, Soils and Climate.
When you factor in low snowpack from the previous water year, drought was already being experienced in the region for the past year. The lower Colorado Basin, Utah and Wyoming have under-performed the most, Meyer said.
SOIL MOISTURE
“Soil moisture is something we keep a very close eye on as we head into the late fall months through the early winter months, because that translates to spring runoff efficiency when it comes time to melt our snowpack. We see a developing situation of soil moisture deficits in in areas that experienced the hotter and drier fall months, which may carry over to a less efficient spring runoff in March and April — when that snowpack melts,” Meyer said. Soil moisture deficits are showing up in the northern portions of the Intermountain West, as well as Arizona and western New Mexico.
However, at least for Colorado and central Utah, it’s a more positive scenario due to the beneficial late fall storms which drove up the topsoil moisture. Hopefully, that translates into a more positive spring runoff efficiency, Meyer added.
Current Drought Conditions across the Intermountain West:
- Arizona: 56.4% in drought — 11.2% in Extreme Drought D3 or greater
- Colorado: 10.4% in drought — 0.3% in Extreme Drought D3 or greater
- New Mexico: 29.1% in drought — 5.2% in Extreme Drought D3 or greater
- Utah: 18.9% in drought — 0% in Extreme Drought D3 or greater
- Wyoming: 96.3% in drought — 22.4% in Extreme Drought D3 or greater
Snow drought updates began being issued in 2018 by the National Integrated Drought Information System evolving from growing interest about its impacts and a need to assemble relevant snow drought data and tools.
“We will update these once a month, beginning this month (December) through June. We rely heavily on NRCS SNOTEL data (the SNOwpackTELemetryNetwork) which is an automated system of snowpack and related climate sensors operated by the Natural Resources Conservation,” said Dan McEvoy, Ph.D., Western Regional Climate Center and the Desert Research Institute. Fifty-seven percent of western U.S. SNOTEL stations are below the media SWE as of Dec. 8. Thirty-seven percent of these stations are below the 30th percentile SWE, McEvoy said.
SNOW MEASURING TOOL
It’s important to measure snowpack temperature related to the timing of snowmelt, which is critical for flooding forecasting and water supply.
“When the snowpack temperature reaches 0 degrees Celsius, it becomes ripe and ready and able to melt, which is part of operational (computer) models used, and it’s important to incorporate this into models to better predict snowmelt and water supply forecasts,” McEvoy said.
A research project, Cooperative Snow Temperature Survey, is now in its second year of development by McEvoy, and DRI’s Anne Heggli and other partners and funded by the Bureau of Reclamation Snow Water supply forecasting. The project uses a non-contact infrared Snow Temperature Profiler with updated technology to learn snow temperature and cold content observations.
Every month in the winter, snow surveyors can use this new non-contact infrared Snow Temperature Profiler, which goes down a hole in the snow, to get a temperature profile up and down the column of snow. This estimates the bulk cold content of the column of snow, which is then compared to model output.
La NINA UPDATE
La Nina hasn’t emerged yet, although it’s expected to become only a weak La Nina in the next couple of months and persist through January-March 2025, Meyer said.
Based on that La Nina expectation, the Climate Prediction Center continues its forecast for the next three months of warmer, drier conditions in the southern U.S., then gradually transitioning to wetter winter months for the northwestern half of Wyoming. In between these two forecast areas, (most of the central states going west to east) there are equal chance of having either warmer/drier or wetter conditions.
Although extended forecast models predict a weather pattern lacking high-impact winter storm systems, there is some hope with it still being early in the winter season, and with variability in late fall and early winter weather patterns, that snow drought conditions can improve, especially at lower elevations.
Recovery from snow drought can be slower in late winter and early spring when snowpack is typically near its peak.
COLORADO
Interestingly, November turned out to be an odd, but positive month, with all of Colorado’s precipitation recorded falling from two storm systems, a Colorado meteorologist said after the webinar.
“The first (of these two storm systems,) which was a very slow moving and moist storm, brought around two-thirds of the monthly accumulations from Nov 4-9. The remaining fell Nov 26-28,” said Kyle Mozley, meteorologist, National Weather Service, Pueblo, Colo. Outside of these two storm systems, it was dry.
The different mountain ranges in Colorado — the Central Mountains, Eastern Mountains and West Slope sites were all above normal.
“And most of the Eastern Mountains have been much-above normal. The San Juan Range didn’t pick up as much with the first system, but got a quick shot near Thanksgiving, which brought their accumulations to near normal. This just goes to show, that one storm, with a slow speed and lots of moisture can look deceiving, and outside of that one storm, the overall monthly totals were dry,” Mozley said.
The Intermountain West Drought Conditions and Outlooks are bi-monthly webinars hosted by the National Integrated Drought Information System.
