Time: 937 AM Thu August 12, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- COOLER WITH CONTINUED HAZE AND A SLIGHT CHANCE FOR LATE AFTERNOON/EVENING SHOWERS/ISOLATED THUNDERSTORMS - The District will experience cooler temperatures today with highs in the upper 80’s over the plains with 70's in the Front Range foothills as a cold front moved through this morning. The haze will continue today but gradual improvement is expected into tomorrow. - Moisture will slowly be on the increase and may result in a few isolated rain showers or weak thunderstorms late this afternoon and evening. There is even a hint that some shower activity may develop over the plains around midnight tonight and linger for a few hours into Friday morning? - Foothill and Palmer Divide locations will have the better chances to experience an isolated high-based shower or weak to moderate thunderstorm today. Generally dry conditions are expected over the majority of the District forecast area until later this evening and there is uncertainty as to whether or not any showers/thunderstorms will come to fruition tonight. Best chances for isolated thunderstorm activity this afternoon over the foothills and Palmer Divide will be from 4-8pm, and over the plains from roughly 8pm this evening until 2am Friday. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.1". Moderate thunderstorms will have the potential to produce rainfall rates of 0.1-0.4" in 10-30 minutes. WORST CASE SCENARIO: A slow moving strong thunderstorm may result in heavy rainfall of 0.4-1.2" in 15-45 minutes. A LOOK AHEAD: A bit of monsoon moisture will return to the District on Friday and increase the chances for thunderstorms area wide. Widely scattered to scattered afternoon thunderstorm coverage is expected with slower moving strong storms capable of producing heavy rainfall that may lead to excessive runoff and possibly flash flooding. Temperatures will continue to run in the 80's for highs over the plains with an improvement in the haze likely. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 800 PM TO 200 AM FRI Trace (40%) to 0.1" (20%) to 0.4" (10%) NONE Broomfield 800 PM TO 200 AM FRI Trace (40%) to 0.1" (20%) to 0.4" (10%) NONE Denver 800 PM TO 200 AM FRI Trace (40%) to 0.1" (20%) to 0.4" (10%) NONE Arapahoe 600 PM TO 200 AM FRI Trace (60%) to 0.1" (30%) to 0.4" (15%) NONE Boulder 600 PM TO 200 AM FRI Trace (40%) to 0.1" (20%) to 0.4" (10%) NONE Douglas 600 PM TO 200 AM FRI Trace (60%) to 0.1" (30%) to 0.4" (15%) NONE Jefferson 600 PM TO 200 AM FRI Trace (40%) to 0.1" (20%) to 0.4" (10%) NONE Foothills above 6500ft       Boulder 400 PM TO 200 AM FRI Trace (75%) to 0.1" (50%) to 0.4" (20%) NONE Douglas 400 PM TO 200 AM FRI Trace (75%) to 0.1" (50%) to 0.4" (20%) NONE Jefferson 400 PM TO 200 AM FRI Trace (75%) to 0.1" (50%) to 0.4" (20%) 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]