Time: 104 PM Wed July 21, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S ISSUED FOR THE ENTIRE DISTRICT - Message 1's have been issued for the entire District and will be valid until 10pm this evening. - Thunderstorms are beginning to develop over the higher terrain to the west with thunderstorms expected to emerge onto the plains between 2-4pm. Prime time for thunderstorm activity is from 2:30-9pm. Additional showers and weaker thunderstorms will remain possible until midnight. 1-2 rounds of thunderstorms are expected with the initial round likely being the strongest. - Relatively slow storm motions from W to E at 10-15mph will allow for extended periods of heavy rain under stronger storms. Storm motions may become erratic at times due to outflow boundaries/gust front interactions. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce 0.2-0.6" in 10-30 minutes. Strong thunderstorms have the potential to produce 0.6-1.8" of heavy rain in 10-30 minutes. WORST CASE SCENARIO: A nearly stationary strong thunderstorm may result in up to 3.0" in 60 minutes or less. COUNTY MESSAGE VALID TIMES PRIME TIME Boulder County 1 100 PM TO 1000 PM 200 PM TO 900 PM Jefferson County 1 100 PM TO 1000 PM 200 PM TO 900 PM Broomfield County 1 100 PM TO 1000 PM 230 PM TO 900 PM Douglas County 1 100 PM TO 1000 PM 200 PM TO 900 PM Adams County 1 100 PM TO 1000 PM 230 PM TO 900 PM Denver County 1 100 PM TO 1000 PM 230 PM TO 900 PM DIA 1 100 PM TO 1000 PM 230 PM TO 900 PM Arapahoe County 1 100 PM TO 1000 PM 230 PM TO 900 PM the City of Aurora 1 100 PM TO 1000 PM 230 PM TO 900 PM Arvada 1 100 PM TO 1000 PM 230 PM TO 900 PM Wheat Ridge 1 100 PM TO 1000 PM 230 PM TO 900 PM Lakewood 1 100 PM TO 1000 PM 230 PM TO 900 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 900 PM 0.2" (80%) to 0.6" (60%) to 1.8" (30%) ISSUED Arapahoe 300 PM TO 900 PM 0.2" (90%) to 0.6" (60%) to 1.8" (30%) ISSUED Broomfield 300 PM TO 900 PM 0.2" (80%) to 0.6" (60%) to 1.8" (30%) ISSUED Denver 300 PM TO 900 PM 0.2" (80%) to 0.6" (60%) to 1.8" (30%) ISSUED Boulder 200 PM TO 900 PM 0.2" (80%) to 0.6" (60%) to 1.8" (30%) ISSUED Douglas 200 PM TO 900 PM 0.2" (90%) to 0.6" (60%) to 1.8" (30%) ISSUED Jefferson 200 PM TO 900 PM 0.2" (80%) to 0.6" (60%) to 1.8" (30%) ISSUED Foothills above 6500ft       Boulder Current TO 900 PM WED 0.2" (95%) to 0.6" (60%) to 1.8" (30%) ISSUED Douglas Current TO 900 PM WED 0.2" (95%) to 0.6" (60%) to 1.8" (30%) ISSUED Jefferson Current TO 900 PM WED 0.2" (95%) to 0.6" (60%) to 1.8" (30%) ISSUED MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]