FTB 08-27-2016: Best Coverage of Storms Over the High Country/Western Slope

Issue Date: 8/27/2016
Issue Time: 9:25 AM

A LOW FLOOD THREAT IS FORECAST TODAY FOR PORTIONS OF THE SAN JUAN MOUNTAINS, SOUTHWEST SLOPE, AND GRAND VALLEY.

A LOW FLOOD THREAT IS ALSO FORECAST TODAY FOR PORTIONS OF THE SOUTHEAST MOUNTAINS, FRONT RANGE, URBAN CORRIDOR, PALMER RIDGE, AND SOUTHEAST PLAINS.

A few degrees of warming aloft will bring slightly warmer afternoon high temperatures across the state, along with a bit of capping to the environment. For the Northeast Plains to the north of I-70, this will act to suppress any shower/thunderstorm chances, keeping the area mostly sunny and warm. Further south, and west over the High Country/Western Slope, isolated-to-scattered showers/storms will overcome the slight warming aloft, owing largely to orographic effects and the passage of a weak, upper-level disturbance. The main impacts from any storm activity today will be gusty winds and lightning, with light-to-moderate rainfall.

IPW_20160827

With that being said, IPW values (shown above) continue to run about average at Grand Junction (green line), dipping to slightly below average at Boulder (blue line) and Schriever AFB (pink line). There’s enough moisture for some concern over locally heavy rainfall, especially with interacting outflow boundaries that locally enhance moisture content. Steeper terrain and burn scars will be the main focal points for today’s low flood threat areas, as well as urban areas with large amounts of impervious surfaces. For more information on timing and rain rates, please see the zone-specific discussions below.

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, jump below the map.

Flood Threat Legend

Zone-Specific Forecasts

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

Isolated-to-widely scattered showers/thunderstorms are expected, mainly along and south of I-70. The best coverage will occur over the Front Range and Southeast Mountains, where orographic effects will play a role in development. Spill over from High Country activity will be the main source of showers/storms over the Urban Corridor, Palmer Ridge, and western portions of the Southeast Plains. Over the far Southeast Plains, a few strong thunderstorms will develop this afternoon/evening, producing strong winds, periods of moderate-to-heavy rainfall, and small hail. Maximum rain rates are as follows:

Urban Corridor and Palmer Ridge: 0.8-1.4 inches/hour
Front Range, Southeast Mountains, and Raton Ridge: 0.6-1.0 inches/hour
Northeast Plains and Southeast Plains: 1.5-2.0 inches/hour

Timing: Noon – Midnight, with a couple showers/weak thunderstorms lingering into the early morning hours

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

A fairly active day is expected, with scattered showers and thunderstorms likely across much of the region. With IPW values around average, widespread heavy precipitation is not expected; rather, the main threats will be gusty winds, lightning, and light-to-moderate rainfall. Locally enhanced moisture from outflow boundaries will provide the opportunity for locally heavy rainfall, and this is taken into consideration with the low flood threat issuance. The best coverage will occur across the higher terrain of the Grand Valley, Southwest Slope, San Juan Mountains, and Southeast Mountains regions. As far as rainfall rates are concerned, most will be 0.25-0.5 inches/hour, with maximum rates of 0.6-1.0 inches/hour.

Timing: 11 AM – 9 PM, with a few lingering showers/weak storms over higher terrain into the early morning hours