Time: 1111 AM Thu August 19, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S ISSUED FOR THE DISTRICT - Message 1's have been issued for all areas of the District except Douglas County at this time and will be valid until 6:00pm this evening. Douglas County may be added over the next hour. - Thunderstorm activity is beginning to initiate over the higher terrain associated with a potent upper level trough of low pressure and will begin to spread out onto the plains shortly. Fast storm motions from SSW to NNE at 30-40mph will limit point rainfall amounts from a singe storm, likely keeping any heavy rainfall under 5 minutes or less in duration for the most part. Training of thunderstorm cells will produce the greatest risk for extended periods of heavy rainfall that may lead to excessive runoff and possibly flash flooding. - Stronger thunderstorm activity today is expected to favor I-70 northward. Strong thunderstorms may also become severe with gusty winds and large hail being the primary threats. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce a 0.1-0.3". Strong thunderstorms will have the potential to produce 0.2-0.6" in 10-20 minutes. Note* - Due to fast storm motions we are using 20-minute rain totals today in the table for the first time this season. WORST CASE SCENARIO: Training of moderate to strong thunderstorm cells may result in up to 1.8" of heavy rainfall in 45-60 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME the City of Aurora 1 Current TO 600 PM 1200 PM TO 500 PM Arapahoe County 1 Current TO 600 PM 1200 PM TO 500 PM DIA 1 Current TO 600 PM 1200 PM TO 500 PM Denver County 1 Current TO 600 PM 1200 PM TO 500 PM Adams County 1 Current TO 600 PM 1200 PM TO 500 PM Broomfield County 1 Current TO 600 PM 1200 PM TO 500 PM Jefferson County 1 Current TO 600 PM 1200 PM TO 500 PM Boulder County 1 Current TO 600 PM 1200 PM TO 500 PM Arvada 1 Current TO 600 PM 1200 PM TO 500 PM Wheat Ridge 1 Current TO 600 PM 1200 PM TO 500 PM Lakewood 1 Current TO 600 PM 1200 PM TO 500 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 20-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 600 PM THU 0.1" (90%) to 0.3" (60%) to 0.6" (30%) ISSUED Arapahoe Current TO 600 PM THU 0.1" (90%) to 0.3" (60%) to 0.6" (30%) ISSUED Boulder Current TO 600 PM THU 0.1" (95%) to 0.3" (65%) to 0.6" (35%) ISSUED Broomfield Current TO 600 PM THU 0.1" (90%) to 0.3" (60%) to 0.6" (30%) ISSUED Denver Current TO 600 PM THU 0.1" (80%) to 0.3" (50%) to 0.6" (25%) ISSUED Douglas Current TO 600 PM THU 0.1" (60%) to 0.3" (40%) to 0.6" (20%) MOD Jefferson Current TO 600 PM THU 0.1" (90%) to 0.3" (60%) to 0.6" (30%) ISSUED Foothills above 6500ft       Boulder Current TO 600 PM THU 0.1" (100%) to 0.3" (75%) to 0.6" (35%) ISSUED Douglas Current TO 600 PM THU 0.1" (65%) to 0.3" (40%) to 0.6" (20%) MOD Jefferson Current TO 600 PM THU 0.1" (100%) to 0.3" (75%) to 0.6" (35%) 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]