FTB 08-22-2017: Heavy Rainfall for Western Colorado

Issue Date: Tuesday, August 22, 2017
Issue Time: 10:15AM MDT

MODERATE flood threat for Southwest Slope, San Juan Mountains and Southeast Mountains

LOW flood threat for all of Colorado excluding eastern plains

Increased cloudiness this morning with the passage of the cold front last night, and temperatures are a bit cooler to start the day. Heavier clouds over the eastern plains is expected to cap convection this afternoon. Some light showers are still occurring across the southern border of the state. Precipitable Water (PW) values are on the rise with Denver at 0.86 inches and Grand Junction at 0.77 inches. PW over the SE Plains is currently 1 inch. A surface boundary may set up over the over the Urban Corridor this afternoon. With a fair amount of instability building throughout the day as the cloud cover breaks up, a few stronger storms may be possible. Over the western portion of the state, more widespread showers are likely. A shortwave trough, associated with the mid-level low pressure system over southern California, will move north throughout the day helping support storms that fire from the diurnal flow. With increase moisture in the atmosphere and slow steering winds under the ridge, these storms have the potential to drop heavy, local precipitation.

Storms that fire over the higher terrain will be more numerous than the previous few days. The storms east of the Continental Divide will favor the higher terrains of the Palmer and Raton Ridge as they slowly drift S/SE off the mountains. A few stronger storms may be found along the southern Urban Corridor this afternoon associated with a convergence boundary. West of the Continental Divide, very widespread showers are likely beginning around 10AM and will intensify with daytime heating. These storms will slowly move north with the shortwave. Storm totals up to 2 inches are possible. Threats include mud flows, debris slides, and road and small stream flooding, especially over burn scars. Sufficient confidence rain rates will be at least 0.5 inches over the Hayden and Junkin burn scars, so a Moderate Flood threat has been issued. Most activity should end around 11PM, but a few showers may linger with the increased mid-level energy overnight. There is a Moderate/Low flood threat for today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below (hover over threat areas for more details). For Zone-Specific forecasts, scroll below the map.

Flood Threat Legend

Zone-Specific Forecasts:

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

Fog and low-level clouds should burn off this morning (west) with mostly cloudy skies over the eastern plains. An increase in thunderstorm activity is expected over the SE Mountains and Front Range. Threats include brief, heavy precipitation. Gusty winds and small hail are possible with the stronger storms. Storms that form near burn scars need to be monitored closely due to high confidence storms that form will have 1-hour rain rates greater than 0.5 inches. 1-hour rain rates will be up to 1.1 inches. A Moderate/Low flood threat has been issued.

Primetime: 12PM to 10PM

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

Showers beginning this morning and increasing in intensity throughout the day. Storm totals up to 2 inches are possible over the San Juan Mountains with other storm totals near 1.5 inches. Threats include mud slides, debris flows and road and small stream flooding. A Moderate/Low flood threat has been issued.

Primetime: 11AM to 11PM