Time: 919 AM Sat August 21, 2021 Forecaster: Brad Simmons

Heavy Precipitation Outlook
Flash Flood Prediction Program

SEASONABLY COOL WITH WIELY SCATTERED AFTERNOON THUNDERSTORMS
-Temperatures will be seasonably cool over the District today with highs reaching the upper 70's to lower 80's over the plains with 60's and 70's in the Front Range foothills. Normal high for Denver today is 87 degrees.
-An upper level disturbance will move in from the SW this afternoon and produce widely scattered showers and thunderstorms over the District into the early evening. Showers and thunderstorms will first develop over the foothills between 1-2pm, then push out onto the plains between 2-4pm with best chances through about 8 or 9pm this evening. 1-2 rounds of showers and thunderstorms are expected.
-Storms will be relatively fast moving from SW to NE at around 20mph and moisture levels are only modest at the surface with dew points in the 40's resulting in storms that develop today generally producing light to briefly moderate rain. A strong slower moving storm or briefly anchored strong thunderstorm on a surface wind convergence line will pose a slight risk for heavy rainfall today.
STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.2" of rain. Weak to moderate thunderstorms will have the potential to produce 0.2-0.6" of moderate to briefly heavy rain in 10-30 minutes.

WORST CASE SCENARIO: A large/slower moving strong thunderstorm may result in up to 1.2" of rain in 60 minutes or less.

A LOOK AHEAD: High pressure will quickly build over the District on Sunday leading to dry conditions and temperatures warming into the upper 80's and lower 90's over the plains.

Location Prime Time 30-Minute Rainfall
and % Probability
Message
Potential
Plains      
Adams 300 PM TO 900 PM
0.1" (90%) to 0.3" (40%) to 0.6" (10%) LOW
Arapahoe 300 PM TO 900 PM
0.1" (90%) to 0.3" (40%) to 0.6" (10%) LOW
Broomfield 300 PM TO 900 PM
0.1" (90%) to 0.3" (40%) to 0.6" (10%) LOW
Denver 300 PM TO 900 PM
0.1" (90%) to 0.3" (40%) to 0.6" (10%) LOW
Boulder 200 PM TO 900 PM
0.1" (90%) to 0.3" (40%) to 0.6" (10%) LOW
Douglas 200 PM TO 900 PM
0.1" (90%) to 0.3" (40%) to 0.6" (10%) LOW
Jefferson 200 PM TO 900 PM
0.1" (90%) to 0.3" (40%) to 0.6" (10%) LOW
Foothills above 6500ft      
Boulder 100 PM TO 900 PM
0.1" (95%) to 0.3" (50%) to 0.6" (15%) LOW
Douglas 100 PM TO 900 PM
0.1" (95%) to 0.3" (50%) to 0.6" (15%) LOW
Jefferson 100 PM TO 900 PM
0.1" (95%) to 0.3" (50%) to 0.6" (15%) LOW
MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS.
https://f2p2.udfcd.org/