Flash Flood Prediction Program

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. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]