FTB 07-28-2016: Hot and Dry West, a Few Strong/Severe Storms East

Issue Date: 7/28/2016
Issue Time: 9:56 AM


A fairly complicated flood threat situation for eastern Colorado awaits us today as different atmospheric components will work against one another. On one hand, the moisture profile that exists currently is top heavy, meaning the most of the moisture lies in the mid-levels. On the other hand, outflow boundaries from earlier convection have moistened the boundary layer over the plains, making it more conducive to heavy rain. How far westward this moistening can go, while fighting dry westerly winds from the mountains, is a big question mark with respect to any storms over the Urban Corridor producing heavy rainfall.

Additionally, the outflow boundaries will have a negative effect on potential for thunderstorms – the cooling associated with them, underneath warm mid-level temperatures, will act to “cap” the environment, effectively limiting thunderstorm potential. And on the other side of that coin, the convergence associated with outflow boundaries could overcome the cap, and strong instability will await with steep mid-level lapse rates. All in all, isolated-to-widely scattered thunderstorms are expected across eastern Colorado, with coverage increasing from west to east. The low flood threat is issued for the potential of heavy rainfall due to increasingly moistened low-levels by outflow boundaries. Storm motions will also be moving fairly briskly to the southeast, so storm motions will help mitigate the flood threat somewhat.


For areas along the Continental Divide and westward, only a couple isolated, high-based showers/thunderstorms are expected. The atmosphere is drier over western Colorado, and nearly all of the moisture resides approximately 4-5.5 km above the surface. This means that any storms that develop will produce gusty winds and lightning, but very little, if any, rainfall at the surface. Virga will likely be the best that any activity can do. Otherwise, it will be a hot day across the region, with lower valleys reaching into the 90s and above 100 in the Colorado River valley near Grand Junction.

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-widely scattered showers/thunderstorms expected throughout today and tonight, with a couple lingering into the morning hours tomorrow. The scenario is a bit jumbled, as described at length above, but the overall result will be a few strong/severe thunderstorms, mainly across the Northeast Plains, northeastern sections of the Southeast Plains, and eastern portions of the Palmer Ridge. These storms will be capable of producing large hail (up to 2-2.5 inches in diameter), strong winds (gusts up to 70 mph), and an isolated tornado or two.

Further west, any strong/severe development will be capable of producing hail up to 1.25 inches in diameter, wind gusts up to 60 mph, and an isolated, weak tornado cannot be ruled out. Storm motions will help mitigate the flood threat, making today a low-end, low flood threat. Maximum rain rates are as follows:

Urban Corridor: 0.8-1.2 inches/hour
Palmer Ridge: 0.8-1.4 inches/hour
Northeast Plains and Southeast Plains: 1.5-2.0 inches/hour

Timing: Noon – 6 AM

Front Range and Southeast Mountains:

A few isolated showers/thunderstorms are expected throughout today and into tonight. Stronger storms will produce gusty winds and small hail, as well as brief bouts with moderate rainfall. There is a low chance (~15%) for redevelopment after midnight tonight as outflow boundaries from plains thunderstorms move into the foothills. Maximum rain rates will be 0.6-0.8 inches/hour.

Timing: 1 PM – 11 PM, with potential redevelopment between 11 PM and 3 AM.

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

A couple isolated, high-based showers/thunderstorms will be all the environment can muster, mainly over the higher terrain of the San Juan Mountains and Southwest Slope. Any activity will produce mainly gusty winds and lightning, with very little, if any, rainfall reaching the surface. Maximum rain rates are less than 0.10 inches/hour. Temperatures will be hot and run about 10 degrees above normal everywhere.

Timing: Noon – 8 PM