Time: 912 AM Sat May 29, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORMS RETURN TO THE DISTRICT/HEAVY RAINFALL POSSIBLE - A cold front is moving through the District this morning and will result winds turning to the E/NE with surface moisture on the increase. Temperatures will be cooler behind the front with highs in the 70's over the plains with 60's in the Front Range foothills. With increased moisture to work with today thunderstorms that develop this afternoon will be capable of producing heavy rainfall and may become severe with large hail and gusty winds being the primary threats. - Thunderstorm activity is expected to initiate between noon and 2pm. Prime time for thunderstorm coverage is from 2-10pm. 1-3 rounds of storms are expected through the evening with additional more isolated rain shower activity continuing possible overnight. Storm motions will be from W to E at around 20mph with stronger storms potentially moving more slowly. - Training of thunderstorm cells or a large, slower moving thunderstorm will produce the greatest risk for extended periods of heavy rainfall that may lead to excessive runoff and possibly flash flooding. Most storms will move fast enough to keep any heavy rainfall relatively brief. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce 0.1-0.3" of rain in 10-30 minutes. Strong thunderstorms will have the potential to produce 0.3-0.8" in 10-30 minutes. WORST CASE SCENARIO: Training of thunderstorm cells or a large/slower moving thunderstorm may result in up to 1.6" of rain in 45-60 minutes. A LOOK AHEAD: Unseasonably cool Sunday with highs struggling to make it out of the 50's over the plains. A lull in the shower activity or minimal rain shower activity Sunday morning is expected to give way to a widespread rain at times through the day. Depending upon heating thunderstorms may develop in the afternoon but if temperatures remain too cool then precipitation likely favors a wetting rain. If thunderstorms develop, heavy rainfall is possible. Additional rain showers expected to continue periodically overnight into Monday morning. Higher elevations of the District above 8k may see some late season snowfall overnight Sunday into Monday. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (20%) MOD Arapahoe 200 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (20%) MOD Broomfield 200 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (15%) MOD Denver 200 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (20%) MOD Boulder 100 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (20%) MOD Douglas 100 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (15%) MOD Jefferson 100 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (15%) MOD Foothills above 6500ft       Boulder 1200 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (15%) MOD Douglas 1200 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (15%) MOD Jefferson 1200 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.8" (15%) MOD MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]