FTB 06-28-2016: Two Distinct Low Flood Threat Areas

Issue Date: 6/28/2016
Issue Time: 10:21 AM


Two distinct areas, for two distinct reasons, will feature low flood threats during this period. The Northeast Plains will experience a period very similar to yesterday’s isolated-to-scattered thunderstorms, which included a few severe storms and bouts with moderate-to-heavy rainfall. The other distinct area will be across southwestern Colorado, namely the Southwest Slope and San Juan Mountains regions. There, better moisture aloft is being transported in from the west/southwest (as shown by the water vapor image/annotations below).

During the afternoon, isolated-to-scattered showers/thunderstorms will be high-based across southwestern Colorado, mainly over the higher terrain. Gusty outflow winds in combination with the high-based thunderstorms producing lightning will heighten fire concerns, mainly over the lower elevations of the Southwest Slope. With that said, as the afternoon turns to evening, moisture will mix down as outflow helps to saturate the lower levels. This increase in the depth of moisture, particularly near the surface, will allow for locally heavy rainfall. Storm motions will help mitigate the flood threat somewhat, but a low flood threat is warranted.


East of the mountains, today will be very similar to yesterday. The main difference is that moisture will be a bit less in comparison, especially along/near the higher terrain. This, combined with the northwest flow regime, will keep the stronger storms further to the east, mainly over the Northeast Plains. For the other regions (Palmer Divide, Urban Corridor, Southeast Plains, and Raton Ridge), isolated showers/thunderstorms will bring mainly gusty winds and lightning, with brief bouts of moderate rainfall. Relatively speaking, the Southeast Plains and Raton Ridge will see the least amount of activity.

For more details, 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

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

Isolated-to-scattered thunderstorms expected. The best coverage will occur over the Northeast Plains, as will the strongest storms. The main threats from storms over the Northeast Plains will be strong winds up to 60 mph, large hail (up to 2.5 inches in diameter), and a brief isolated tornado or two.

The Urban Corridor, Palmer Ridge, Raton Ridge, and Southeast Plains will see more isolated coverage, with more “garden variety” intensity. The main threats from these storms will be gusty winds, lightning, and small hail. Maximum rain rates are as follows:

Northeast Plains: 2.0-2.8 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 0.4-0.8 inches/hour
Southeast Plains: 1.0-1.5 inches/hour

Timing: 2 PM – Midnight, with a couple isolated storms continuing over the Plains into the early morning hours

Front Range, Northern Mountains, Central Mountains, San Luis Valley, and Southeast Mountains:

Isolated-to-scattered showers/thunderstorms expected. Storms will develop over the higher terrain, briefly drifting over lower valleys. The main impacts from any activity will be gusty winds, lightning, and light rain. Maximum rain rates will be 0.5-0.8 inches/hour.

Timing: 11 AM – 10 PM

Northwest Slope and Grand Valley:

Mostly sunny and hot will be the main weather story today. Over the higher terrain, isolated, high-based, dry thunderstorms will develop this afternoon/evening. This will elevate fire concerns in these regions as gusty outflow winds and very little rain will accompany any cloud-to-ground lightning.

Timing: 2 PM – 10 PM

San Juan Mountains and Southwest Slope:

Isolated-to-scattered thunderstorms are expected, mainly over the higher terrain. During the afternoon, storms will be high-based, producing more wind and lightning than rain. As the afternoon turns to evening, however, moisture will mix down into the low-levels, providing the opportunity for locally heavy rainfall. Thus, the issuance of the low flood threat. Steep terrain, burn scars, and low lying areas will be the main areas of concern for any flood/heavy rain issues. Maximum rain rates will be 1.0-1.5 inches/hour.

Timing: 11 AM – 9 PM