— The HIGH<\/strong> threat will persist through at least the early overnight hours<\/em><\/span>
— A MODERATE<\/strong> flood threat has been posted for parts of the Northeast Plains, Northern Mountains, Central Mountains and San Juan Mountains<\/em>
— A LOW<\/strong> flood threat has been posted for parts of the San Luis Valley, Northwest Slope, Grand Valley and Southwest Slope<\/em>
— An afternoon update is possible today<\/em><\/span><\/p>\n
On the 45th anniversary of the devastating Big Thompson floods that changed the way flood detection was done in Colorado, we are expecting a very active day of heavy rainfall and flooding across major parts of the state. In fact, all 14 of our forecast zones are under some kind of flood threat today.<\/p>\n
Let’s start first with the most vulnerable areas, which will be the I-25 corridor south of Denver through the New Mexico border as well as southeast Colorado. A cold front raced through the state overnight, bringing down high temperatures from the recent heat wave. In fact, this will mean instability will not be all that impressive today anywhere in the state, with perhaps up to 1,500 J\/kg at most expected in the Southeast Plains. However, the lack of instability will be easily overcome by very high moisture content through the entire atmosphere. Denver’s PW<\/span> came in at 1.20 inches today, significantly above normal for the date. Up to 1.5 inches of PW<\/span> is currently estimated in eastern Colorado and this plume of moisture will move southward today after the cold front passage. A decaying mesoscale storm complex, with a distinct anti-cyclonic circulation aloft, was noted along the northeast CO border. The main impact of this will be to limit instability over the I-76 corridor, likely suppressing heavy rainfall activity. Further south and west, enough breaks in the clouds today will support moist adiabat type soundings with extremely efficient rainfall generation expected. With the sheer amount of moisture available, we expect multiple rounds of heavy rainfall along the entire high terrain east of the Continental Divide<\/span>. Storms will then spill over into the foothills and Southeast Plains by later in the afternoon and persist well into the overnight hours towards the OK\/KS border. In particular, the threat today is not so much from short-term 1-hour rainfall but more so the 3-6 hour timeframe where multiple heavy rainfall cores could support up to 4-7 inches of rainfall over parts of the Palmer Ridge, Southeast Mountains, Raton Ridge and Southeast Plains. With the spatial extent of heavy rainfall, in addition to the normal threat of flash flooding<\/span>, riverine flooding of creeks and streams will be likely today. Base flows on the larger rivers are not all the high, mitigating any large-scale riverine flooding. However, there is a chance of a flood wave, albeit brief, along the Arkansas River this evening and overnight.<\/p>\n
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