Time: 727 PM Wed July 21, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S CONTINUE VALID, HEAVY RAINFALL THREAT DIMINISHING - Message 1's will continue valid although the threat for heavy rainfall is diminishing now that temperatures are cooling. - Strong/slow moving thunderstorms concentrated just S and W of the District over Clear Creek County earlier this afternoon and more recently over SE Douglas County. Currently there is a gust front travelling northward from the Douglas County storms but is failing to initiate new thunderstorms with temperatures now in the 80's. - There is weak thunderstorm activity to the NW of the District at this time and should these storms survive their journey E/SE into the District or interact with the boundary moving northward heavy rainfall may still occur in areas that have had minimal storm activity up to this point. However, with the cooling temperatures thunderstorms will likely not be as strong as earlier in the day but it will not necessarily require a strong thunderstorm to produce brief heavy rainfall. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce 0.1-0.5" in 10-30 minutes. Strong thunderstorms have the potential to produce 0.5-1.5" of heavy rain in 10-30 minutes. WORST CASE SCENARIO: A nearly stationary strong thunderstorm may result in up to 2.5" in 60 minutes or less. COUNTY MESSAGE VALID TIMES PRIME TIME Boulder County 1 100 PM TO 1000 PM Current TO 900 PM Jefferson County 1 100 PM TO 1000 PM Current TO 900 PM Broomfield County 1 100 PM TO 1000 PM Current TO 900 PM Douglas County 1 100 PM TO 1000 PM Current TO 900 PM Adams County 1 100 PM TO 1000 PM Current TO 900 PM Denver County 1 100 PM TO 1000 PM Current TO 900 PM DIA 1 100 PM TO 1000 PM Current TO 900 PM Arapahoe County 1 100 PM TO 1000 PM Current TO 900 PM the City of Aurora 1 100 PM TO 1000 PM Current TO 900 PM Arvada 1 100 PM TO 1000 PM Current TO 900 PM Wheat Ridge 1 100 PM TO 1000 PM Current TO 900 PM Lakewood 1 100 PM TO 1000 PM Current TO 900 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 1000 PM WED 0.1" (40%) to 0.5" (20%) to 1.5" (10%) ISSUED Arapahoe Current TO 1000 PM WED 0.1" (80%) to 0.5" (50%) to 1.5" (20%) ISSUED Boulder Current TO 1000 PM WED 0.1" (75%) to 0.5" (50%) to 1.5" (20%) ISSUED Broomfield Current TO 1000 PM WED 0.1" (60%) to 0.5" (30%) to 1.5" (15%) ISSUED Denver Current TO 1000 PM WED 0.1" (40%) to 0.5" (20%) to 1.5" (10%) ISSUED Douglas Current TO 1000 PM WED 0.1" (80%) to 0.5" (50%) to 1.5" (20%) ISSUED Jefferson Current TO 1000 PM WED 0.1" (75%) to 0.5" (50%) to 1.5" (20%) ISSUED Foothills above 6500ft       Boulder Current TO 1000 PM WED 0.1" (80%) to 0.5" (40%) to 1.5" (20%) ISSUED Douglas Current TO 1000 PM WED 0.1" (80%) to 0.5" (40%) to 1.5" (20%) ISSUED Jefferson Current TO 1000 PM WED 0.1" (80%) to 0.5" (40%) to 1.5" (20%) 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]