FTB 07-30-2020: High Moisture Associated with the Passing Trough Returns the Flood Threat

Issue Date: Thursday, July 30th, 2020
Issue Time: 9:50AM MDT

— A LOW flood threat has been issued for the Northeast Plains, Southeast Plains, Front Range, Urban Corridor, and portions of the Palmer Ridge

Back to issuing flood threats after a quick, one-day break. The satellite image below shows two strong and distinct air masses at play over the state. The much drier air to our west/southwest from the High (clear conditions) and the more unsettled, wetter air mass to the northeast from the passing trough (generating showers and cloud cover). This upper trough, that has been affecting the weather the last couple of days, will finally push south and brush Colorado’s eastern border producing unsettled weather over the eastern plains. Mid-level energy and ample moisture with the feature is expected to generate non-severe thunderstorms and multiple rounds of rainfall over the Northeast Plains. With these storms starting by late morning, increasing in intensity by this afternoon, and lingering through the evening, a Low flood threat has been issued. While precipitation totals could be on the higher end, hopefully the expected lower 1-hour rain rates can temper the flood threat somewhat. Threats include field ponding, road flooding, and flooding of low-lying areas.

A second, weaker shortwave will slide south in to the northern high terrains later this afternoon with the NNW flow aloft, and help spark some isolated thunderstorms in tandem with upslope flow over the Front Range. It’s likely that the storms that form over the Northeast Plains will push a moisture boundary back to the west, so decent rainfall accumulations will be possible under the stronger storms as dew points in the plains are in the upper 50Fs to low 60Fs. Again, storm motion will be relatively fast, so the flood threat will be limited to only the stronger storms that develop. Additionally, a quick 0.5 in 30-min could cause some nuisance road flooding or ponding as storms track south along the I-25 corridor. A Low flood threat has been issued for these regions.

Over western Colorado, it has quickly dried out from the monsoon moisture early this week with PW measured at 0.50 inches this morning. Capping aloft and a dry atmosphere will drop-off the rainfall chances to nearly nil today. Outsides of some cloud cover over the mountains near the Continental Divide, it should be a bluebird day.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Urban Corridor, Front Range, Northeast Plains, Palmer Ridge, Southeast Plains, Southeast Mountains, & Raton Ridge:

Multiple rounds of rain with some non-severe thunderstorms will be possible over the Northeast Plains by late this morning into the evening with the passing trough. Isolated storm totals up to 2.2 inches will be possible by Friday morning with the training rainfall. A stronger storm could also push into the area that forms over the Cheyenne Ridge. A Low flood threat has been issued for field ponding and flooding of roads/low-lying areas.

Over the Front Range in to the Urban Corridor, isolated max 1-hour rain rates up to 1 inches will be possible if the moisture can push westward into the foothills and I-25 corridor. A quick 0.5 inches in 30 minutes could also produce some nuisance flooding in roads and low-lying areas. A Low flood threat has been issued. Unsure how far south across the I-25 corridor storms will be able to track before decreasing instability puts a cap on the convection.

Primetime: 11AM to 9PM

San Juan Mountains, Central Mountains, Northern Mountains, Southwest Slope, Northwest Slope, Grand Valley, & San Luis Valley:

High temperatures will be on the rise today with the bluebird conditions. Highs are expected to reach into 90Fs over the lower elevations with 70Fs in the mountains. A few clouds are forecast by this afternoon over the peaks near the Continental Divide, but rainfall is not forecast.