Flash Flood Prediction Program

Time: 420 PM Sat May 8, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- OVERNIGHT SHOWERS/THUNDERSTORMS LIKELY IMPACT THE DISTRICT - A round of thunderstorms moved through the District earlier, mainly impacting areas E of I-25. Conditions are generally quiet over the District currently and an isolated rain shower or weak thunderstorm cannot be ruled out through sunset. Our attention will focus on a secondary cold front will move through this evening and could generate thunderstorm activity initially before transitioning to scattered light rain showers. - There remains a good deal of uncertainty in regards to precipitation tonight but the best chances for thunderstorm activity looks to be from 9pm tonight to 2am Sunday. The strength of the storms is anticipated to be weak to briefly moderate but the storms could be efficient rainfall producers and anchor or move very slowly as surface flow becomes "upslope" northeasterly behind the front. After 2am, additional light rain showers are likely into Sunday morning. - Updates may need to be issued this evening/overnight if conditions warrant. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.2" of precipitation. Moderate thunderstorms will have the potential to produce 0.2-0.6" in 10-30 minutes. WORST CASE SCENARIO: A strong thunderstorm or stationary weak to moderate thunderstorm cells may result in up to 1.2" of rain in 45-75 minutes. A LOOK AHEAD: A chance for widely scattered light showers Sunday morning gives way to additional showers and possibly 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 weather as of late. 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 accumulating snow all areas of the District 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 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Arapahoe 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Boulder 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Broomfield 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Denver 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Douglas 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Jefferson 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Foothills above 6500ft       Boulder 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Douglas 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) LOW Jefferson 1000 PM TO 1000 AM SUN Trace (95%) to 0.3" (60%) to 0.6" (15%) 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]