Time: 859 AM Thu May 20, 2021 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- WARMER TODAY WITH A VERY SLIGHT CHANCE FOR HIGH-BASED AFTERNOON THUNDERSTORMS - SW Flow aloft this afternoon will help usher in warmer, drier air, bringing high temperatures into the upper 70's to low 80's on the plains with low 70's along the foothills. A very slight chance this afternoon for high-based thunderstorms, favoring areas in the District that are north of I-70. - Widely scattered rain showers/thunderstorms will move out onto the plains between 1-3pm. Minimal, if any, rainfall will be expected, generally up to a trace, although an isolated 0.10" of rainfall cannot be completely ruled out. Biggest threat for storms today will be gusty wind and the occasional lightning strike. Storm motions will be relatively quick moving from SW to NE between 10-15mph helping limit any point rainfall amounts that do occur. Any shower or thunderstorm activity will move out of the District between 6-7pm with skies clearing into the evening. - Mild and dry conditions through the overnight as lows drop into the upper 40's to low 50's on the plains, with low to mid 40's along the foothills. STORM RAINFALL POTENTIAL AND DURATION: Weak thunderstorms will have the potential to produce TR-0.1" in 10-30 minutes. WORST CASE SCENARIO: A moderate to strong thunderstorms will have the potential to produce 0.1-0.3" in 10-30 minutes. A LOOK AHEAD: SW flow aloft will strengthen over the next few days resulting in better chances for afternoon and evening rain showers/thunderstorms. Temperatures will remain in the upper 70's to low 80's Friday and Saturday with the best chance for heavy rainfall coming into the region Saturday afternoon and evening. A cold front moves through early Sunday morning bringing cooler temperatures overall with a continued chance for afternoon rain showers/thunderstorms. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 700 PM Trace (40%) to 0.1" (15%) to 0.3" (5%) NONE Arapahoe 200 PM TO 700 PM Trace (30%) to 0.1" (5%) NONE Boulder 200 PM TO 700 PM Trace (40%) to 0.1" (10%) NONE Broomfield 200 PM TO 700 PM Trace (40%) to 0.1" (15%) to 0.3" (5%) NONE Denver 200 PM TO 700 PM Trace (30%) to 0.1" (5%) NONE Douglas 200 PM TO 700 PM Trace (30%) to 0.1" (5%) NONE Jefferson 200 PM TO 700 PM Trace (30%) to 0.1" (5%) NONE Foothills above 6500ft       Boulder 100 PM TO 600 PM Trace (50%) to 0.1" (20%) to 0.3" (5%) NONE Douglas 100 PM TO 600 PM Trace (30%) to 0.1" (5%) NONE Jefferson 100 PM TO 600 PM Trace (40%) to 0.1" (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]