FTB 06-23-2020: Slow Moving Storms Return the Flood Threat to the Southeast Mountains and Raton Ridge

Issue Date: Tuesday, June 23rd, 2020
Issue Time: 9:05AM MDT

— A MODERATE flood threat has been issued for the Spring Creek burn area

— A LOW flood threat has been issued for the Southeast Mountains and Raton Ridge

Similar set up to yesterday with the main difference being that jet is well to the northeast over Nebraska. The High pressure system is located off the Baja/California coast, and it will keep weak northwesterly flow aloft over the state. Taking a look at the low-level water vapor imagery below, there looks to be moisture over the majority of the state (blue shades) minus the dry southwest corner (orange/yellow shade). Moisture in the boundary layer may decrease a bit throughout the day, but overall decent moisture should remain east of the green dashed line below. With slow storm motion to the southeast, storms should be able to drop a little more rainfall today, and trailing storms will also help increase 24-hour totals. Additionally, without much upper level support and no shortwave insight upstream, storms should be on the weaker end today and will likely pulse in intensity. Still, a couple weak thunderstorms may pop up near the southern border with the main threats being small hail and brief, gusty winds.

Guidance is indicating decent moisture along and just west of the southern Southeast Mountains, and enhanced convergence along the Raton Ridge/Wet Mountains may allow max 1-hour rain rates to reach up to 1.1 inches. Thus, a Low flood threat has been issued for the area. There’s also a good chance that a storm may form or track over the Spring Creek burn area. With max 1-hour rain rates in that area up to 0.75 inches possible, a Moderate flood threat has been issued. Burn scar flood threats include flash flooding of local streams, mud flows and debris slides, so use caution near the area.

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:

Southeast Mountains, Front Range, Palmer Ridge, & Raton Ridge:

Easterly and southeasterly flow of the surface winds will help initiate convection over the eastern mountains by early afternoon. Storms will be slow moving, which will allow rain totals to increase when compared to yesterday; however, storms will be small in area. With the weak steering flow, storms will barely make it into the Urban Corridor and will favor the elevated ridges as they make their way southeast. Max 1-hour rain rates up to 0.50 inches will be possible over the Front Range with very isolated totals just under 1 inch possible over the southern Palmer Ridge.

Rain rates will increase further south due to slightly higher lowl-level moisture, so rain rates up to 1.1 inches will be possible over the Palmer Ridge and Wet Mountains. Therefore, a Low flood threat has been issued. There is also a good probability that totals near the Spring Creek burn area will reach around 0.75 inches, so a Moderate flood threat has been issued. Field ponding, local stream flash flooding and mud flows/debris slides (burn area) will be possible this afternoon. Without any upper level support, storms should end a couple hours after sundown.

Primetime: 1PM to 10:30PM

Southeast Plains & Northeast Plains:

The Northeast Plains look to remain relatively dry this afternoon. There may be a weak storm that moves into Weld County that forms on the Cheyenne Ridge, but 1-hour rain rates will only reach about 0.50 inches. Further south over the eastern Palmer Ridge and Southeast Plains, coverage of storms looks a little better this afternoon when compared to yesterday. The severe threat is a little less, but small hail and wind gusts up to 45 mph may be possible under stronger thunderstorms that form. Isolated max 1-hour rain rates up to 1.25 inches will be possible.

Primetime: 1PM to 11PM

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

It should be mostly dry again with highs similar to yesterday or a couple degrees warmer. A couple high-based showers may develop over the highest terrains of the San Juan, Northern, and Central Mountains near the Divide this afternoon. However, totals should remain under 0.10 inches. The best chance for weak rainfall will be over the eastern San Juan Mountains, and a weak storm may track into the southern San Luis Valley. Expect brief gusty winds as the storms evaporate off the high terrains. There may also be some light rainfall over the western facing Southeast Mountains, but totals should remain under 0.25 inches. Lastly, a Red Flag Warning has been issued for portions of the Southwest Slope. Even though there will be lighter surface winds under the building ridge, patchy 10 to 15 mph winds are still expected in a region with very dry fuels and low relative humidity, which would allow fires to spread quickly. Please tune into NWS Grand Junction for the latest on the fire weather.