FTB 09-17-2017: A Few Stronger Storms for Eastern Colorado

Issue Date: Sunday, September 17th, 2017
Issue Time: 9:00 AM MDT

— Flooding is NOT expected today

A couple ingredients will come together for a more active period, and each have been highlighted on the surface map below. First of all, southwesterly flow aloft (red arrow) has increased in the wake of yesterday’s exiting trough and today’s approaching shortwave disturbance. This has helped to increase moisture across the state as well, pushing precipitable water values near, or just above, normal for the date. At the surface, a quasi-stationary front is draped along the I-25 corridor, allowing moist upslope flow to continue into eastern Colorado. The different flow directions create a “turning” with height, which will provide the necessary shear for a few strong-to-severe thunderstorms across eastern Colorado today/tonight.

Across the high country, showers and thunderstorms are expected to be of the garden variety, producing brief periods of rainfall and gusty winds. All activity across the state is expected to move east-northeastward at a decent pace, limiting rainfall in any one location, so flash flooding is not a concern. For more details, please see the zone-specific forecast 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, scroll below the map.

Zone-Specific Forecasts:

Urban Corridor, Palmer Ridge, Raton Ridge, Northeast Plains, and Southeast Plains:

Scattered showers and thunderstorms are expected, first impacting western areas near the interface with the mountains and moving east-northeastward with time. A few strong-to-severe storms are likely for areas along/south of I-70, with the main threats being large hail, strong winds, and an isolated tornado or two. Brief periods of heavy rain will accompany stronger storms, but storm motions will limit the amount of rainfall in any one location. Due to this, flash flooding is not a concern, but isolated locations of street flooding in poorly drained areas are possible. Maximum rain rates are as follows:

Urban Corridor: 0.5-0.8 inches/hour
Palmer Ridge: 0.5-1.0 inches/hour
Northeast Plains, Southeast Plains, and Raton Ridge: 0.8-1.25 inches/hour

Timing: 1 PM – 10 PM for the Urban Corridor, Noon – Midnight for the Raton Ridge, 2 PM – Midnight for the Palmer Ridge, and 2 PM – 3 AM for the Southeast Plains and Northeast Plains

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

Scattered showers and thunderstorms are expected today, beginning later this morning and continuing into the nighttime hours. A couple showers/weak thunderstorms may persist into the early morning hours tomorrow over the higher elevations of central Colorado. As mentioned above, storm motions will keep storms from producing flash flooding, but brief periods of heavy rain will attend the strongest storms. Otherwise, gusty winds and lightning will be the main threats. Maximum rain rates are as follows:

Northwest Slope: 0.05-0.15 inches/hour
Northern Mountains, Front Range, Central Mountains, and Southeast Mountains: 0.5-0.9 inches/hour
San Juan Mountains, Southwest Slope, Grand Valley, and San Luis Valley: 0.4-0.8 inches/hour

Timing: 11 AM – 9 PM, with a few lingering showers/weak thunderstorms into the early morning hours.