Flash Flood Prediction Program

Time: 1108 AM Mon May 17, 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 Boulder, Jefferson and Douglas Counties and will be valid until 10:00pm this evening. Additional Message 1's will likely be issued for the remainder of the District in the coming hours. - Thunderstorms are just beginning to initiate over the foothills, a little earlier than expected and will become more numerous into the afternoon. Thunderstorms that develop today will be very capable of producing heavy rainfall that may lead to excessive runoff and possibly flash flooding. Storm motions will be slow, at 10mph or less and thunderstorms may have a tendency to anchor along the foothill/plains interface potentially producing moderate to heavy rainfall for an extended period of time. - Thunderstorms are expected to remain over the higher terrain until early to mid afternoon then become widespread into the evening. Best chances for thunderstorm activity will be until around 10:00pm with scattered showers until midnight. After midnight a drying trend is expected but there will continue to be a modest chance for light rain into Tuesday morning. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce 0.1-0.4" in 10-30 minutes. Moderate to strong thunderstorms. Moderate to strong thunderstorms will have the potential to produce 0.4-1.0" in 10-30 minutes. WORST CASE SCENARIO: A strong thunderstorm becomes stationary producing an extended period of heavy rainfall with up to 2.0" in 60 minutes or less. COUNTY MESSAGE VALID TIMES PRIME TIME Jefferson County 1 Current TO 1000 PM 100 PM TO 900 PM Boulder County 1 Current TO 1000 PM 100 PM TO 900 PM Douglas County 1 Current TO 1000 PM 100 PM TO 900 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1159 PM 0.1" (90%) to 0.4" (50%) to 1.0" (15%) MOD Arapahoe 200 PM TO 1159 PM 0.1" (90%) to 0.4" (50%) to 1.0" (15%) MOD Broomfield 200 PM TO 1159 PM 0.1" (90%) to 0.4" (50%) to 1.0" (15%) MOD Denver 200 PM TO 1159 PM 0.1" (90%) to 0.4" (50%) to 1.0" (15%) MOD Boulder 100 PM TO 1159 PM 0.1" (95%) to 0.4" (60%) to 1.0" (20%) ISSUED Jefferson 100 PM TO 1159 PM 0.1" (95%) to 0.4" (60%) to 1.0" (20%) ISSUED Douglas Current TO 1159 PM MON 0.1" (95%) to 0.4" (60%) to 1.0" (20%) ISSUED Foothills above 6500ft       Boulder 100 PM TO 1159 PM 0.1" (100%) to 0.4" (75%) to 1.0" (25%) ISSUED Douglas Current TO 1159 PM MON 0.1" (100%) to 0.4" (75%) to 1.0" (25%) ISSUED Jefferson Current TO 1159 PM MON 0.1" (100%) to 0.4" (75%) to 1.0" (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]