Recent monsoon storms have delivered much-needed moisture to southwest Colorado after a dry spring and record-low snowpack.
But the National Weather Service says the rain has not erased the region’s deeper drought conditions.
Erin Walter, a service hydrologist with the National Weather Service in Grand Junction, said the monsoon arrived later than usual this year, with moisture increasing more noticeably during July.
Many areas around the Four Corners have since received above-average precipitation for the month.
Walter said the rain has improved some short-term drought indicators, particularly surface soil moisture. In parts of southwest Colorado, the upper layer of soil is now close to saturated.
Conditions remain drier farther underground, however.
“So far, the monsoon has provided some improvements via that meteorological indicator,” Walter said. “However, you still have other categories or ways of defining and measuring drought.”
Those other measurements include streamflow, reservoir storage, crop conditions and the health of trees and other vegetation.
Walter said soil moisture estimates roughly one meter below the surface continue to show below-normal saturation. That deeper moisture is important for trees and other plants with longer root systems.
Streamflows also remain low across much of the region. Some monitoring stations have reported flows below average or near record lows for this time of year.
The difference illustrates why a landscape can turn green after several storms while the larger water system remains under stress.
Walter said monsoon rainfall can contribute some water to rivers and reservoirs, but southwest Colorado’s water supply depends much more heavily on winter snowpack and spring runoff.
“The monsoon rain can help, but we do rely on that snowpack to supply all of our reservoirs,” Walter said.
She cited McPhee Reservoir as an example. Average inflow during May can exceed 84,000 acre-feet as mountain snow melts. Average July inflow is less than 12,000 acre-feet.
That means even an active monsoon usually cannot replace the water lost during a poor snow year.
The storms can still provide meaningful benefits. Rain can improve soil moisture, support vegetation and temporarily reduce some fire-weather concerns.
Higher atmospheric moisture generally reduces the hot and dry conditions associated with critical fire weather. But monsoon thunderstorms can create a different set of hazards, including flash flooding, hail and strong outflow winds.
Walter said a recent thunderstorm in Cortez produced flash flooding, hail and wind damage.
Heavy rainfall can be especially dangerous over recently burned areas.
Severe fires can change the structure of the soil, making it harder for water to soak into the ground. Intense rainfall can then run quickly downhill, increasing the risk of flash floods and debris flows.
Walter encouraged people traveling or recreating near flood-prone areas and recent burn scars to check the forecast before heading out.
She also encouraged residents to report hail, flooding, wind damage and other storm impacts to the National Weather Service.
Those reports are particularly important in southwest Colorado because radar coverage is limited. Forecast offices in Colorado, Utah, Arizona and New Mexico all provide partial coverage of the Four Corners, but localized storms can still be difficult to observe remotely.
The Climate Prediction Center’s outlook continues to favor wetter-than-normal conditions across southwest Colorado through the remainder of the summer.
Walter said the region has roughly a 30% to 40% chance of receiving above-normal precipitation. The outlook for August through October also leans wetter than normal, although confidence is higher over Arizona.
Continued rain could provide additional relief for soils, vegetation and fire conditions.
But Walter said long-term water supplies will still depend largely on what happens during the coming winter.
The monsoon has helped. For reservoirs, streams and the deeper drought, however, the region still has substantial ground to make up.
