FTB 05-27-2020: Scattered Storms Return to the Mountains with the Passage of Another Shortwave

Issue Date: Wednesday, May 27th, 2020
Issue Time: 9AM MDT

— A LOW flood threat has been issued for the Deckers and Spring Creek burn areas

Below is a lower-level water vapor image with a 500mb pressure and wind analysis overlaid on top. You can still see the main low still to our southeast, and a distinct shortwave moving through the flow that is currently located over the Great Basin (dashed orange line).  North and northwest flow over Colorado will send this moderately strong shortwave across the state today, which will help produce scattered afternoon storms over the mountains and Northwest Slope. With shallow surface moisture and a lot of dry air aloft, storms for the most part are expected to be high-based, produce gusty winds and possibly small hail. Only moderate rainfall is forecast to accompany the strongest storms, but trailing storms may help increase totals over certain areas in a 2 to 3 hour period. Thus, a Low flood has been issued for the Deckers and Spring Creek burn areas, which have lower thresholds for flash flooding criteria. Storms will spill into the adjacent plains with the northwest steering winds, and the best chance for rainfall at the lower elevations will be over the Palmer Ridge and south.

Today is the annual sediment flushing exercise at Cherry Creek Reservoir, so please use caution along the trails. More information can be found here: Annual Sediment Flush – Cherry Creek

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:

Northwest Slope, Northern Mountains, Front Range, Central Mountains, & Southeast Mountains:

Scattered afternoon showers and thunderstorms return to these forecast regions this afternoon. Over western Colorado, storms will favor the higher terrains and areas near the Continental Divide with 1-hour rain rates up to 0.40 inches possible. With coverage more spotty, trailing storms are less likely, but a few areas could receive just over a half inch by late Wednesday evening.

Coverage is expected to increase over the southern Front Range and Southeast Mountains due to slightly higher moisture values. Max 1-hour rain rates up to 0.60 inches will be possible with 2-3 hour totals up to 0.75 inches possible over isolated areas. Thus, a Low flood threat has been issued for the Deckers and Spring Creek burn areas as chances for trailing storms increase over these areas. Storms are expected to start dissipating over the Southeast Mountains and adjacent plains by midnight.

Primetime: 1PM to 1AM

Urban Corridor, Palmer Ridge, Northeast Plains, Raton Ridge, San Luis Valley, & Southeast Plains:

Activity over the mountains will likely spill over into the immediate adjacent plains later this afternoon favoring the Palmer Ridge and south for accumulations. Max 1-hour rain rates up to 0.60 inches will be possible with most lower elevations areas receiving under 0.15 inches and plenty of gusty outflow winds. A couple storms may wander off the eastern San Juan Mountains into the San Luis Valley with isolated 24-hour totals up to 0.20 inches possible by morning.

Primetime: 3PM to 1AM

Grand Valley, Southwest Slope, & San Juan Mountains:

An isolated, high-based storm or two may form over the western San Juan Mountains, but more storms are more likely to form over the eastern San Juans. Max 1-hour rain rates up to 0.40 inches will be possible, but most storms will produce less than 0.15 inches. Other lower elevation areas will remain dry this afternoon with high temperatures forecast to reach the mid to upper 80Fs.

Primetime: 1PM to 10PM