—<\/span> The HIGH<\/strong> threat persists into the late evening hours, especially for northern areas<\/em><\/span>
— A MODERATE<\/strong> flood threat has been posted for parts of the Northwest Slope, Grand Valley, Southwest Slope, Southeast Mountains and Front Range<\/em>
— A LOW<\/strong> flood threat has been posted for parts of the San Luis Valley<\/em>
— An NWS<\/span> Flood Warning<\/span> is in effect for the Arkansas River at La Junta and downstream areas<\/span><\/em><\/p>\n
While the past few days’ worth of elevated flood threats has been primarily reliant on copious moisture (and high elevation heating) to drive the heavy rainfall, an important new feature today ups the ante and warrants a HIGH flood threat for the higher terrain. As shown in the visible satellite picture below, this feature is a pronounced disturbance, currently over eastern UT, that is embedded in the upper-level monsoon<\/span> ridge. This disturbance will trek slowly eastward, bringing in cooling temperatures aloft, promoting a widespread<\/span> tropical-like rainfall for Colorado’s entire higher terrain.<\/p>\n A strong moisture gradient exists this morning with Denver’s PW<\/span> of 0.79 inches contrasting with Grand Junction’s 1.30 inches. For the western slope, this high of a PW<\/span> is within ~10% of their record. Furthermore, Albuquerque’s PW<\/span> of 1.26 inches and Salt Lake City’s 1.35 inches summarize just how expansive this monsoonal moisture plume is. An expansive cloud deck with showers and weak storms is already ongoing across the western slope, which will limit instability to ~600 J\/kg or less. However, just like with Saturday’s rainfall over the Arkansas River basin, instability is essentially a useless metric today since tropical rainfall can occur with almost no instability. The presence of synoptic scale upward motion from the disturbance will be enough to cause a ~12 hour period of persistently moderate to heavy rainfall over the higher terrain, which is what warrants the HIGH threat. In addition to the threat of heavy rainfall, widespread<\/span> areas have now received more than 1 inch of rain over the past week or so. Thus, there will be a particularly elevated threat of mud flows and debris slides that can respond to rainfall with very long lag times of days.<\/p>\n For the eastern Colorado plains, there will be a sharp gradient in the precipitation shield so that elevations below 8,000 feet are not expected to see much if any rainfall.<\/p>\n
![\"\"](\"https:\/\/archive-coftb.dewberryanalytics.com\/wp-content\/uploads\/2021\/08\/vis_markup.png\")
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