Time: 547 PM Thu August 19, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S WILL BE ALLOWED TO EXPIRE AT 6PM/ADDITIONAL ROUND OF SHOWERS AND THUNDERSTORMS POSSIBLE OVERNIGHT... - Message 1's will be allowed to expire at 6pm as the threat for heavy rainfall has ended, at least through the rest of today... Thunderstorms that moved through the District earlier today produced brief periods of heavy rainfall, hail and even spawned multiple NWS tornado warnings. - The stronger thunderstorm activity has pushed well east of the District with additional rain showers and weak thunderstorms remaining possible into the evening but heavy rainfall is no longer a threat until another upper level wave moves through overnight. After midnight tonight another round of rain showers and possibly thunderstorms associated with the strong upper level low pressure system to the NW is expected to move through sometime between 1-7am Friday morning. - An additional HPO will be issued this evening to assess the overnight heavy rainfall threat and another Message 1 period may be needed to cover the potential for heavy rainfall. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.1" of rain. Moderate thunderstorms will have the potential to produce 0.1-0.4" in 10-30 minutes. WORST CASE SCENARIO: A strong thunderstorm is able to develop with the potential to produce heavy rainfall of 0.3-0.8" in 10-30 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Boulder County 1 Current TO 600 PM Current TO 600 PM Jefferson County 1 Current TO 600 PM Current TO 600 PM Broomfield County 1 Current TO 600 PM Current TO 600 PM Douglas County 1 Current TO 600 PM Current TO 600 PM Adams County 1 Current TO 600 PM Current TO 600 PM Denver County 1 Current TO 600 PM Current TO 600 PM DIA 1 Current TO 600 PM Current TO 600 PM Arapahoe County 1 Current TO 600 PM Current TO 600 PM the City of Aurora 1 Current TO 600 PM Current TO 600 PM Arvada 1 Current TO 600 PM Current TO 600 PM Wheat Ridge 1 Current TO 600 PM Current TO 600 PM Lakewood 1 Current TO 600 PM Current TO 600 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Arapahoe Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Boulder Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Broomfield Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Denver Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Douglas Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Jefferson Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Foothills above 6500ft       Boulder Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Douglas Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE Jefferson Current TO 900 PM THU Trace (60%) to 0.2" (20%) to 0.4" (10%) NONE MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]