Flash Flood Prediction Program

Time: 206 AM Fri August 20, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S ISSUED FOR PORTIONS OF THE DISTRICT - Message 1's have been issued for Adams, Boulder, Broomfield and Jefferson Counties and will be valid until 5am. Additional Counties may be added to the Message 1's over the next 30-60mins. - Upper level low pressure system is producing a nocturnal round of showers and thunderstorms that will impact NW areas of the District into the pre-dawn hours. The showers and thunderstorms are fast moving from SSW to NNE at around 30mph but will be capable of producing brief heavy rainfall that may lead to excessive runoff. - Best chances for thunderstorms will be through about 4am as a line of storms moves through N/NW areas of the District. By 5am the showers and thunderstorms are expected to have pushed to the N/NE out of the District. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.2" of rain. Moderate to strong thunderstorms will have the potential to produce 0.3-0.8"of heavy rain in 10-30 minutes. WORST CASE SCENARIO: Training of thunderstorm cells results in up to 1.5" of heavy rain in 45-60 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Lakewood 1 Current TO 500 AM 230 AM TO 400 AM Wheat Ridge 1 Current TO 500 AM 230 AM TO 400 AM Arvada 1 Current TO 500 AM 230 AM TO 400 AM Adams County 1 Current TO 500 AM 230 AM TO 400 AM Broomfield County 1 Current TO 500 AM 230 AM TO 400 AM Jefferson County 1 Current TO 500 AM 230 AM TO 400 AM Boulder County 1 Current TO 500 AM 230 AM TO 400 AM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 500 AM FRI 0.1" (60%) to 0.3" (40%) to 0.8" (20%) ISSUED Arapahoe Current TO 500 AM FRI 0.1" (40%) to 0.3" (20%) to 0.8" (10%) LOW Boulder Current TO 500 AM FRI 0.1" (90%) to 0.3" (60%) to 0.8" (30%) ISSUED Broomfield Current TO 500 AM FRI 0.1" (75%) to 0.3" (50%) to 0.8" (25%) ISSUED Denver Current TO 500 AM FRI 0.1" (50%) to 0.3" (30%) to 0.8" (15%) MOD Douglas Current TO 500 AM FRI 0.1" (40%) to 0.3" (20%) to 0.8" (10%) LOW Jefferson Current TO 500 AM FRI 0.1" (80%) to 0.3" (50%) to 0.8" (25%) ISSUED Foothills above 6500ft       Boulder Current TO 500 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (35%) ISSUED Douglas Current TO 500 AM FRI 0.1" (40%) to 0.3" (20%) to 0.8" (10%) LOW Jefferson Current TO 500 AM FRI 0.1" (80%) to 0.3" (50%) to 0.8" (25%) 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]