While drought conditions and wildfires have been the big story across Colorado early this summer, today’s outlook is for widespread thunderstorms with heavy rainfall potential across the eastern mountain ranges and adjacent foothills and plains of Colorado. This wet pattern will only be temporary as conditions will dry out again over the weekend, but as the main ridge of high pressure shifts from the Southeast U.S. to the Southwest U.S., southeasterly low level winds around the center of high pressure are transporting significant amounts of moisture into Eastern Colorado.
The image below (courtesy of weathermodels.com) is from the European (ECMWF) Model, showing the projected percent of average precipitable water anomaly for this afternoon. Precipitable water is essentially a measure of total moisture in the atmosphere from the surface to the upper levels, and is a good general indicator of heavy rainfall potential with thunderstorms during the summertime. For this afternoon, we will see well above average precipitable water values – as much as 150% of average across Eastern Colorado!
In addition, weak upper level winds are going to result in slow storm motions with thunderstorms this afternoon. With significant moisture in place and the potential for strong, slow moving thunderstorms, there is going to be an elevated threat for heavy rainfall and flash flooding across the Front Range today. Recent fires across portions of the Southern Front Range will result in elevated concerns for flash flooding as well, since recently burned areas can absorb very little moisture in a short period of time before excessive runoff occurs. It’s the caveat often experienced in Colorado and the Western U.S. when moisture is needed during periods of drought and fire activity, but too much too quickly can also cause big problems.
Our brief period of high moisture and heavy rainfall potential will come to an end this weekend with a return to drier weather and hot temperatures. The North American Monsoon is expected to get going this weekend and early next week, but initially the deepest monsoon moisture will be located farther west across Arizona and Utah with less moisture over Colorado. Portions of western Colorado should start to see a gradual increase in moisture heading into next week, but it may take a bit longer for a more favorable and consistent fetch of monsoonal moisture to take hold across the Front Range.