Flash Flood Prediction Program

Time: 1147 AM Fri June 25, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- HEAVY RAINFALL PRODUCING THUNDERSTORMS EXPECTED THIS AFTERNOON AND EVENING - Trough of low pressure moving through NE CO will result in a wet period setting up later today into the weekend. As the upper level disturbance approaches thunderstorms will be on the increase early this afternoon becoming scattered to numerous at times into the evening. With abundant moisture at the surface thunderstorms that develop today will be very capable of producing heavy rainfall that may lead to excessive runoff and possibly flash flooding. - Individual thunderstorms will be relatively fast moving from W to E at 20-25mph helping limit point rainfall amounts from a single storm. A cold front moving through this afternoon may be a focus for stronger storms with the potential to produce extended periods of heavy rainfall. Training of thunderstorm cells could also be a culprit for linger duration heavy rainfall. Prime time for thunderstorms is from roughly 1pm to 11pm. - After 10 or 11pm the convective nature of the precipitation is expected to transition to a more stratiform rainfall and the heavy rainfall threat is expected to wane with additional light to moderate rain showers continuing overnight. If precipitation does not transition to a general rain then Message 1's may need to be extended late this evening. STORM RAINFALL POTENTIAL AND DURATION: Moderate to strong thunderstorms will have the potential to produce 0.4-1.2" in 10-30 minutes. WORST CASE SCENARIO: A large slower moving thunderstorm or training of thunderstorm cells will have the potential to produce up to 2.5" in 45-75 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Denver County 1 Current TO 1159 PM 1230 PM TO 1100 PM Adams County 1 Current TO 1159 PM 1230 PM TO 1100 PM Douglas County 1 Current TO 1159 PM 1230 PM TO 1100 PM Broomfield County 1 Current TO 1159 PM 1230 PM TO 1100 PM Jefferson County 1 Current TO 1159 PM 1230 PM TO 1100 PM Boulder County 1 Current TO 1159 PM 1230 PM TO 1100 PM DIA 1 Current TO 1159 PM 1230 PM TO 1100 PM Arapahoe County 1 Current TO 1159 PM 1230 PM TO 1100 PM the City of Aurora 1 Current TO 1159 PM 1230 PM TO 1100 PM Arvada 1 Current TO 1159 PM 1230 PM TO 1100 PM Wheat Ridge 1 Current TO 1159 PM 1230 PM TO 1100 PM Lakewood 1 Current TO 1159 PM 1230 PM TO 1100 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Arapahoe Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Boulder Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Broomfield Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Denver Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Douglas Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Jefferson Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Foothills above 6500ft       Boulder Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Douglas Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) ISSUED Jefferson Current TO 1159 PM FRI 0.1" (100%) to 0.5" (75%) to 1.2" (50%) 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]