Issue Date: Thursday, August 8th, 2019
Issue Time: 10:15AM MDT
–A MODERATE flood threat has been issued over portions of the Northeast Plains, Southeast Plains, Raton Ridge and Palmer Ridge. This includes the Junkins burn area.
-A LOW flood threat has been issued for the Front Range, Urban Corridor, Northeast Plains and the Spring Creek burn area.
PM update (3PM): An additional MODERATE flood threat has now been issued over the Northeast Plains. Dew points over the area have been steadily increasing from this morning, resulting in higher instability and increasing rain rates. Another round of storms are expected to move in off of the Cheyenne Ridge this evening, and we have increasing confidence that storms should produce 1-hour rain rates around 1.75 inches. Isolated storm totals due to multiple rounds of rainfall are forecast to be just over 2.5 inches. The threat over this area will end after midnight.
Another round of widespread thunderstorms is expected today across the eastern plains. Surface moisture is high throughout the state again with dew points (green contours below) measuring in the 50°Fs and 60°Fs over the western valleys and eastern plains respectively. PW values this morning at Denver were measured at 1.17 inches and should continue to increase throughout the day, which is very high for this time of year. The subtropical high is now centered over south-central New Mexico, which will create westerly steering flow aloft over our area. A jet streak, which can be seen in the yellow shading of the mid-level water vapor imagery below, will bring in dry air and fast winds to the west today. This should mix out a lot of the mid-level moisture seen in today’s Grand Junction sounding. This feature will also help to keep storms moving and keep rain rates below flood threat criteria. A vorticity maximum is forecast to form in the lee of the Rockies over southern Wyoming this afternoon, which will provide forcing for widespread severe thunderstorms over the adjacent and far eastern plains. In the moisture rich environment, all storms that form today will be capable of heavy rainfall, thus the large Low threat area.
Morning cloud cover over the northern mountain ranges and portions of the eastern plains will help retain surface moisture this morning. Surface winds from the east and southeast should keep low level moisture from mixing out as well. The surface low pressure system centered over the Oklahoma Panhandle (marked “L”) below will help drive these low level winds.
Storms are forecast to begin over the Continental Divide by mid-day and move over the adjacent plains early this afternoon. Slow upper level steering flows from the northwest between 10 and 15 mph will allow storms to produce heavy rainfall over a 1-2 hour period. Storms will likely be crossing the I-25 interstate around rush hour, so please use extra caution as water will likely pool with the heavy rainfall this afternoon. As the storms move east, a few severe thunderstorms will be possible as indicated by the skinny CAPE profile in the Denver sounding this morning. Threats further to the west include wind gusts in excess of 60mph and hail between 1.75 and 2 inches (isolated). Rain rates will also increase as storms slow down and enter dew points in the 60°Fs to the east. Thus, there is a Moderate flood threat issued, which is anticipated to last until 4AM tomorrow morning.
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.
Zone-Specific Forecasts:
Front Range, Urban Corridor, Southeast Mountains, Raton Ridge, Palmer Ridge, Northeast Plains, Southeast Plains:
Cloud cover over the mountains has limited instability, which will confine max 1-hour rain rates over the northern Front Range and northern Urban Corridor to 0.75 inches. Over the foothills of the southern Front Range and southern Urban Corridor max 1-hour rainfall rates up to 1 inch are possible. The southeast mountains will have weak downsloping winds and faster upper level winds, which will keep max 1-hour rainfall rates around 0.4 inches. If a storm tracks over the Spring Creek burn area, there may be some flash flooding issues, so the Low flood threat has been pulled over this area. Due to the more eastern location of the Wet Mountains, higher dew points will be likely, so a Moderate flood threat has been issued over the Junkins burn area. Threats over the recent burn areas (if a storm tracks over them) include flash flooding of small rivers and streams, debris slides and mud flows. The National Weather Service has issued a Flash Flood Watch over the eastern mountains to the south of Teller County, as well as El Paso, Pueblo and eastern Las Animas Counties.
Over the Northeast Plains, a Low flood threat has been issued with more isolated max 1-hour rainfall rates up to 1.5 inches possible. Looks like multiple rounds of rainfall (including overnight rain) could create isolated storm totals up to 2.25 inches by morning. Further south, max 1-hour rainfall rates up to 2 inches are possible over the Southeast Plains, with up to 1.75 inches possible over the eastern Palmer Ridge. Due to slow steering winds mentioned above, isolated 2-3 hour storm totals up to 2.75 inches are possible by morning. Threats today include local stream/creek flash flooding, field ponding, street flooding and arroyo flash flooding. This is an overnight Moderate threat with the heavy rainfall ending by 4AM.
Primetime: 11AM to 4AM
Northwest Slope, Northern Mountains, Grand Valley, Southwest Slope, Central Mountains, San Juan Mountains, San Luis Valley:
Westerly dry air and fast wind speeds will keep rainfall below threat criteria today. Chances for precipitation are high over the higher terrain favoring the southeastern San Juan Mountains and the Roan Cliffs/Flat Top region. Max 1-hour rainfall rates to 0.8 inches will be possible over these areas with other storms producing closer to 0.25 inches. There are some isolated storms possible over the San Luis Valley, but totals will likely remain below 0.10 inches.
Primetime: 11AM to 6PM
