FTB 08-31-2017: Disturbance To Trigger Widespread Showers/Storms, But Intensity Limited

Issue Date: Thursday, August 31, 2017
Issue Time: 9:35AM MDT

MODERATE flood threat for Junkins and Beulah Hill burn scars
LOW flood threat for Hayden Pass burn scar

Changes are on the way this morning for Colorado’s weather. As shown in the water vapor image, below, a strong shortwave disturbance has made it to the Great Basin as of this morning. The dynamics with this disturbance are forcing upward motion to its east – seen by the wide swath of mainly mid-level clouds across UT, WY and northern CO. Precipitable water values have increased slightly to 0.82 inches at Grand Junction (mostly mid-level moisture with surface dew point of only 36 F) and 0.65 inches at Denver. As the disturbance continues to move eastward, it will generate widespread afternoon and evening showers and thunderstorms. The highest coverage will be over the High Country where instability will be uncapped. Farther east of the Plains, limited instability will only allow for isolated to widely scattered showers and perhaps a weak thunderstorm.

Rainfall rates this afternoon are expected to stay below flood threat levels, with the only exception being across the burn scars of the Sangre de Cristo and Wet mountains. These fresh scars only require 0.5 inches per hour of rainfall to cause mud flows and flash flooding. This appears probable today, especially over the Wet Mountains. Thus, a Moderate flood threat has been posted for the Junkins and Beulah Hill scars, while a Low threat has been posted for the Hayden Pass scar.

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:

Partly cloudy this morning, then increasing cloudiness with numerous showers and thunderstorms possible. Highest coverage will be over the higher terrain east of the Continental Divide as well as the Cheyenne, Palmer and Raton ridges. Farther east, coverage will be isolated to scattered. Max 1-hour rain rates up to 0.9 inch closer to the foothills and 1.3 inches across the eastern plains. Max 24-hour rainfall up to 1.3 inches possible across the High Country. Gusty winds could accompany the strongest storms. A Moderate flood threat has been issued for the Junkins and Beulah Hill scars, while a Low threat has been issued for the Hayden Pass scar for mud flows and flash flooding.

Primetime: 1PM to 9PM

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

Partly to mostly cloudy with numerous showers and thunderstorms likely this afternoon. Highest coverage will be over the foothills and higher terrain. Max 1-hour rainfall up to 0.75 inches is possible, with max 24-hour rainfall up to 1.2 inch especially over higher elevation locations. Gusty winds will accompany the strongest cells. Flooding is not expected today.

Primetime: 12PM to 9PM