Fall weather patterns may bring limited relief to Colorado’s thirst for moisture, but experts at the Colorado Climate Center at Colorado State University warn that enough fall moisture to make a significant difference to the drought-ridden state is unlikely.
July proved to be another month with hotter than average temperatures and below average precipitation across the state, further contributing to drought conditions. A few mountain showers provided localized moisture, but most areas were dry. Colorado’s eastern plains were particularly dry with several areas receiving less than a quarter-inch of rainfall for the entire month and a few locations without measurable precipitation at all during July. In some areas, July’s formidable weather broke heat and dry conditions records.
"Weather patterns have been changing in August," said state climatologist and atmospheric science Professor Roger Pielke Sr. "We’ve already experienced three strong, fall-like fronts that have dropped moisture in localized storms around the state. Large thunderstorms in late August have behaved more like spring and early summer storms, dropping locally heavy rains and hail over portions of the plains."
Although those storms have released some moisture and probably will continue to do so for a few weeks, Colorado Climate Center experts said the storms are not as much help as one might hope.
"The potential for more widespread precipitation in the coming weeks means that some increase in soil moisture this fall is possible," said Nolan Doesken, research associate at the Colorado Climate Center. "This is critical for Colorado grasslands and winter-planted wheat, which could have a better year next year if we can muster up a few good fall rains and wet snows. However, fall is usually not a period that supplies enough precipitation to impact drought. "In fact, fall often holds periods of sustained dry, sunny weather that can be accompanied by periods of strong winds," Doesken said. "Fast-spreading wildfires have been a problem in Colorado in September when these conditions are common, so we might be particularly vulnerable to additional fall fires this year."
Summer and fall rains also contribute little or nothing to streamflow and reservoir levels. Despite some recent rainfall, most Colorado rivers and streams continue to flow at or below record levels and reservoirs continue to be drawn down. Many irrigation reservoirs are nearly empty, and the summer irrigation season has come to a premature end for some of Colorado’s irrigated crops.
Continued lower than average streamflow this winter means that many municipal-use reservoirs will continue to be slowly drawn down. Urban water restrictions will likely continue to tighten as surface-water reserves dwindle.
In addition, reservoirs are so depleted that a single average snowpack and precipitation year will not replenish reservoirs, especially the larger ones. A good portion of the precipitation that does arrive this winter will first recharge soil moisture instead of reservoirs. This means that, with average snowpack this year, Coloradoans should still expect below average runoff and surface water supplies for next year.
Current indicators make it difficult to confidently predict weather patterns for this winter, according to Climate Center researchers. But 110 year’s worth of historic data shows that, although two consecutive winters of extreme low snowpack are unprecedented, it usually takes at least one and sometimes several years to truly come out of an extreme drought of the magnitude of the current year. With average snowpack, some parts of the state may recover more quickly than others, but it is rare for the entire state to recover at the same time.