FTB 07-22-2018: Another Unsettled Period for Colorado

Issue Date: 7/22/2018
Issue Time: 8:02 AM

A LOW FLOOD THREAT IS FORECAST FOR PORTIONS OF THE NORTHERN MOUNTAINS, FRONT RANGE, CENTRAL MOUNTAINS, SOUTHEAST MOUNTAINS, URBAN CORRIDOR, PALMER RIDGE, RATON RIDGE, NORTHEAST PLAINS, AND SOUTHEAST PLAINS.
A LOW FLOOD THREAT IS FORECAST FOR THE 416 FIRE AND BURRO FIRE BURN SCARS IN SOUTHWEST COLORADO.

The upper-level high pressure is centered over central New Mexico this morning, placing most of Colorado under moist west-southwesterly flow aloft. The high pressure is not expected to shift much throughout the day, so expect this mid-level moisture stream to continue into tomorrow. This moisture has already fueled a couple isolated showers over the northern high country this morning, and will set the stage for another day/night of scattered showers/thunderstorms across Colorado.

Due to hot temperatures expected again today, low relative humidity near the surface will once again work against the moisture aloft. This will reduce the precipitation efficiency of storm activity, especially during the afternoon and early evening hours when temperatures are at their warmest. Just as yesterday, it will take storms saturating the lower levels themselves to get heavy rainfall to the surface. This is most likely for storms east of the mountains, where outflow from adjacent storms will aid nearby storms’ efforts to moisten the near-surface air.

Dewpoints in the 50s and 60s across eastern Colorado suggest the threat for periods of moderate-to-heavy rain, as well as a few strong-to-severe thunderstorms. Relatively quick storm motions to the east at 15-20 mph will limit the flood threat somewhat, so a low flood threat is all that is warranted for those areas. For areas west of the Continental Divide, it looks like another day of more wind than rain. However, due to the higher terrain of the San Juan Mountains and Southwest Slope receiving about 0.05-0.1 inches of rainfall this morning, a low flood threat has been issued for the 416 Fire and Burro Fire scars.

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

Another day of scattered showers/thunderstorms expected. During the afternoon, activity will produce more wind than rain. As the day wears on, outflow from adjacent storms will help to moisten the low-levels, increasing the risk of heavy rain, especially for areas east of the mountains. Maximum rain rates are as follows:

Front Range and Southeast Mountains: 0.8-1.1 inches/hour
Urban Corridor, Palmer Ridge, and Raton Ridge: 1.0-1.4 inches/hour
Northeast Plains and Southeast Plains: 1.5-2.5 inches/hour

Timing: Noon – 10 PM for the mountains, 1 PM – 11 PM for the Urban Corridor, and 2 PM – Midnight for the Palmer Ridge, Northeast Plains, and Southeast Plains. A couple showers/thunderstorms will linger into the early morning hours near the CO/KS border.

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

Scattered showers/thunderstorms are expected again today. A few showers are ongoing north of I-70 already this morning. Due to warm temperatures, relative humidity remains low in the low-levels, and the monsoonal moisture remains confined to the mid-levels. This will lead to storms producing more wind than rain, with the exceptions being eastern portions of the Northern Mountains and Central Mountains, due to their proximity of better low-level moisture from the east, thus their inclusion in the low flood threat area. The 416 Fire and Burro Fire have been issued a low flood threat, due to the light rainfall that fell this morning adding a bit of moisture to the sensitive soils. Generally speaking, rain rates will be 0.1-0.3 inches/hour, with stronger storms in the low flood threat area having maximum rain rates around 0.8-1.0 inches/hour.

Timing: 11 AM – 8 PM for the Southwest Slope, San Juan Mountains, San Luis Valley. 11 AM – 10 PM for all other regions. A few showers will linger into the early morning hours over the higher terrain (mainly north of I-70 where moisture will be best).