FTB 08-10-2019: Rinse and Repeat Pattern with More Widespread Thunderstorm Activity and Overnight Rainfall for the Mountains

Issue Date: Saturday, August 10th, 2019
Issue Time: 9:12AM MDT

— A MODERATE flood threat has been issued for the 416 burn area
— A LOW flood threat has been issued for the San Juan Mountains, Central Mountains, Southeast Mountains, southern Front Range, southern Urban Corridor, Palmer Ridge, Raton Ridge, Northeast Plains and portions of the Grand Valley and Southwest Slope. This includes the following burn areas: Junkins, Hayden Pass, Spring Creek and Lake Christine. This includes the following burn areas: Junkins, Hayden Pass, Spring Creek and Lake Christine.

Similar set up to yesterday with the moisture tap still in place. The subtropical high is currently over Texas, so this feature has shifted a little bit more to the east. In turn, high moisture has re-worked its way back into western Colorado. Shortwaves continue to work across the state as they round the high moving to the NNW. The shortwave that brought late night showers to the high terrains is still moving north, so some isolated thunder and light rain is currently occurring over the Northern Front Range the adjacent Urban Corridor. Today and tomorrow, more pronounced shortwaves will work their way into the state from New Mexico and Arizona. With PW still near an inch at Denver and 0.86 inches at Grand Junction this morning, expecting widespread rainfall throughout the day with some thunderstorms later this afternoon. Moisture will increase throughout the day as well, so heavy rainfall will be possible with the storms today.

Storms are anticipated to kick off around noon over the higher elevations with help from the approaching shortwave. Storm motion will be fairly quick, but with the moisture rich environment, storms will still be capable of producing some impressive rain rates in a 30-45 minute span. Note, that as the storms move into the eastern plains they will gain a more westerly steering component. Another flooding issue will be multiple storms tracking over the same area, which if this happens, will cause an increase in accumulations over the mountains or adjacent plains. Therefore, special attention should be paid to the Palmer Ridge area this afternoon as it has been pounded by rainfall the last couple of days. This means soils are saturated and primed for increased runoff and flash flooding. It may only take a quick 0.5 inches in 30 minutes or less. A few severe thunderstorms are likely over the far eastern Plains as storms make their way into the high CAPE and decent, but low, shear environment. Large hail (1 to 1.25 inches) and brief strong wind (gusts 40 – 50 mph) will be possible with these storms. An additional set severe thunderstorms, capable of very heavy rainfall are anticipated to set up along a dry line, but guidance is showing the heaviest rainfall to our east, over Kansas.

Lastly, there are also flooding concerns over recent burn areas. Please use caution if storms track over any recent burn area as flash flooding, debris slides and mud flows are possible. We have included the 416 burn area in the threat area today due to heavy rainfall from yesterday making the burn scar more susceptible to flooding issues. Additional showers and weak thunderstorms are possible overnight in the southwest mountains with the next passing shortwave, which would affect this burn area. Rain rates should be gradual enough they won’t cause many other issues, but storms may linger over one area for a bit. Thus, the Low flood threat.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Flood Threat Legend

 

Zone-Specific Forecasts:

Front Range, Southeast Mountains, Urban Corridor, Palmer Ridge, Raton Ridge, Northeast Plains, Southeast Plains:

Widespread showers and thunderstorms anticipated today favoring the Front Range and northern Southeast Mountains. Max 1-hour rain rates up to 0.75 inches (north) and 0.6 inches (south) will be possible. As storms move into the adjacent plains, the best moisture will be along the Palmer Ridge and over the Northeast Plains. Storm totals will be close to 1 inch (west) and up to 1.75 inches to the east near the CO/NE/KS borders. Slightly lower totals are anticipated over the far northeast corner associated with the passing shortwave, which will begin around 11AM. Some isolated severe thunderstorms may also be possible along the dry line over the far Southeast Plains. Max 1-hour rain rates up to 1 inch may be possible. This area lies in the Low flood threat, which includes the Junkins, Hayden Pass and Spring Creek burn areas. Threats today include flash flooding of local streams/creeks, lowland flooding of roads/ditches and field ponding. Additionally, mud flows and debris slides may be especially possible over the Spring Creek burn area. A few storms may linger over the Southeast Mountains overnight, which may affect the Spring Creek burn area.

Primetime: Noon to 5AM

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

Storms this afternoon should be mostly confined to the high terrains over and along the Continental Divide. Very isolated max 2-3 hour totals (trailing storms) up to 0.75 inches will be possible. The higher terrains of the adjacent plains may see up to 0.5 inches in isolated pockets as well, but most storms will produce around 0.3 inches. Another set of storms with more coverage moves into the San Juan and Central Mountains between 10PM and midnight. This could cause (isolated) storm totals between 1 and 1.25 inches by morning with more general totals near 0.75 inches. The most likely locations of the heavier rainfall is forecast over the San Juan Mountains and southeast corner of the Central Mountains. The 416 burn area has a Moderate threat issued because of this and a lot of rainfall near/over the scar yesterday. The Lake Christine burn area is also included in the Low threat, although the higher totals will likely be to the east of the area.

Primetime: 12PM through Morning