Flash Flood Prediction Program

Time: 949 AM Sat May 8, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- COOLER/BREEZY WITH A CHANCE FOR AFTERNOON/EVENING THUNDERSTORMS AND ADDITIONAL SHOWERS OVERNIGHT - A cold front will be moving through the District this morning lowering temperatures into the upper 60's and 70's for highs over the plains. Winds will be on the increase from the N into the 10-20mph range with gusts to 30mph or more possible. - A lot of uncertainty in regards to precipitation today/tonight... There will be good upper level lift and enough moisture to fuel a line or two of thunderstorms this afternoon, but the moisture is not very deep over the District and the freezing level will be lowering through the day which may result in stronger storms producing hail/gusty winds versus heavy rainfall? Regardless, there will be a chance for thunderstorms over the District today, starting as early as noon over the foothills. - A round or two of showers and weak to moderate thunderstorms is expected into the evening, stronger storms likely remain E of I-25. Best chances for thunderstorms will be between 1-7pm. Moderate/strong storms will have the potential to produce brief moderate/heavy rain as well as hail. A dry period is then expected ahead of a secondary cold front that moves in during the evening. Additional showers and possibly a brief period of thunderstorm activity then looks to become possible between 10pm-2am. After 2am Sunday, additional light rain showers are likely through the morning. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.2" of precipitation. Moderate to strong thunderstorms will have the potential to produce 0.2-0.6" in 10-30 minutes. WORST CASE SCENARIO: A slow moving strong thunderstorm or training of thunderstorm cells may result in up to 1.0" of rain in 45-75 minutes. A LOOK AHEAD: A chance for widely scattered light showers Sunday morning gives way to additional showers and isolated thunderstorms in the afternoon. Thunderstorms if they develop may result in a threat for flooding as the ground does not need much moisture to become saturated with the wet spring so far. A soaking rain is then expected to set up during the evening Sunday and continue overnight into the day on Monday. Smaller creeks and streams susceptible to runoff will be running high. The snow line may lower to around 6k briefly Monday morning before rising again. Additional rain showers (or snow above 7 or 8k) are likely all day Monday continuing into the evening. Monday night into Tuesday temperatures are expected to become cold enough for most areas to see some snow down to 5k into Tuesday morning. 1-2" of moisture or more is possible over the District in the form of rain or melted snow equivalent from Sunday through Tuesday. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 100 PM TO 700 PM Trace (95%) to 0.2" (65%) to 0.6" (30%) LOW Arapahoe 100 PM TO 700 PM Trace (95%) to 0.2" (65%) to 0.6" (30%) LOW Boulder 100 PM TO 700 PM Trace (95%) to 0.2" (60%) to 0.6" (15%) LOW Broomfield 100 PM TO 700 PM Trace (95%) to 0.2" (60%) to 0.6" (15%) LOW Denver 100 PM TO 700 PM Trace (95%) to 0.2" (65%) to 0.6" (30%) LOW Douglas 100 PM TO 700 PM Trace (95%) to 0.2" (60%) to 0.6" (20%) LOW Jefferson 100 PM TO 700 PM Trace (95%) to 0.2" (60%) to 0.6" (15%) LOW Foothills above 6500ft       Boulder 1200 PM TO 700 PM Trace (95%) to 0.2" (60%) to 0.6" (10%) LOW Douglas 1200 PM TO 700 PM Trace (95%) to 0.2" (60%) to 0.6" (10%) LOW Jefferson 1200 PM TO 700 PM Trace (95%) to 0.2" (60%) to 0.6" (10%) LOW MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]