FTB 05-31-2020: Diurnal Thunderstorms Return to the Mountains

Issue Date: Sunday, May 31st, 2020
Issue Time: 9:20AM MDT

— A LOW flood threat has been issued for the Deckers and Spring Creek burn areas

Slight pattern shift from the previous few days. The upper low that was off the coast of California is now an open, upper wave over the Pacific Northwest (dashed purple line). There is some lift still associated with the trough (upper jet) as seen by the cloud cover to our northwest. Several small mid-level disturbances are expected to continue to move through the flow around the ridge. In fact, these are what is helping produce the cloud cover currently seen over western Colorado and the mountains. Meanwhile, the axis of the ridge is building to our east with an elongated 500mb high over northern New Mexico and Texas. What does all of this mean for rainfall chances today?

As seen by the cloud cover below, there is still quite a bit of moisture trapped under the ridge. This will help produce another round of diurnally driven thunderstorms. Storms will again favor the mountains for coverage, although with only weak mid-level disturbances moving through the flow, storms are not expected to be as widespread today. Additionally, southwest flow aloft has picked up over the state, which will turn more westerly throughout the day. This will decrease the rain rate efficiency as surface moisture begins to mix out. Therefore, expecting a downtick in dew points, and the main threat from storms today to be wind. With storm motion from east to west this afternoon, storms will likely spill into the adjacent plains again. They have the best chance of survival over the ridges (Cheyenne, Palmer, Raton), and are not expected to survive too far into the eastern plains.

A Low flood threat has been issued for the Deckers and Spring Creek burn areas due to trailing storms increasing totals and semi-saturated soils from rainfall the last few days. Elsewhere, flooding is not expected.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. If there is a threat, hover over the threat areas for more details, and click on burn areas to learn more about them. For Zone-Specific forecasts, scroll below the threat map.

Zone-Specific Forecasts:

Front Range, Southeast Mountains, San Juan Mountains, Northern Mountains, & Central Mountains:

The Northern Mountains look to remain mostly dry this afternoon, but a few dry thunderstorms may be possible over the northern border. Over the Central and San Juan Mountains, storms will favor the areas near and along the Continental Divide. Max 1-hour rain rates up to 0.50 inches will be possible along with strong downdraft winds. Over the Front Range, rain rates up to 0.75 inches will be possible under the strongest cores. The Southeast Mountains will likely see a drop in rain rates with max 1-hour rain rates just over 0.50 inches possible. Should a storm or multiple storms track directly over burn areas, flash flooding, debris slides and mud flows may be possible. A Low flood threat has been issued for the Deckers and Spring Creek burn areas due to 1-3 hour totals likely exceeding 0.50 inches in this scenario and rain helping to saturate flood prone soils over the last few days. Weak rainfall may persist overnight over the southern mountains, but overnight flooding is not forecast.

Primetime: 1PM to 12AM

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

Storms will push off into the plains earlier this afternoon with steering winds turning more westerly. Best chance for rainfall will be over the Raton and Palmer Ridge where isolated max 1-hour rain around 0.75 inches will be possible. Storms are not expected to survive long if they make it over the Northeast and Southeast Plains (lower elevations), but a quick 0.25-0.50 inches still seems feasible. Strong outflow winds and small hail will be the main threats from the storms today.

Primetime: 1:30PM to 12AM

Northwest Slope, Grand Valley, Southwest Slope, & San Luis Valley:

Less chance for rainfall at the lower elevations this afternoon, but chances of storms producing strong wind gusts will go up (50 mph+). Max 1-hour rain rates will be around and under 0.15 inches for storms that do move off the mountains in the lower terrains. The best chance for accumulations will be over the Northwest Slope. As expected, flooding is not forecast.

Primetime: 1PM to 9PM