Flash Flood Prediction Program

Time: 846 AM Sat May 20, 2023 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- CLOUDY/HAZY AND SLIGHTLY WARMER WITH ANY SHOWERS/THUNDERSTORMS ONE AGAIN LIMITED TO THE FOOTHILLS AND PALMER DIVIDE Not much overall change in the weather pattern as cloudy and hazy conditions remain in place this morning. Skies are expected to gradually clear through the afternoon with a good chance for afternoon and evening rain showers/isolated thunderstorms along the higher terrain and into the foothills. There will be a slight chance a few of these storms will move onto the plains and into the District this afternoon and into the evening. The best chance for storms in the District will be from 3pm through 9pm, with a few lingering rain showers possible through 10pm before skies clear into the overnight. Typical rain showers will only produce a TR-0.2”, however, a slower moving thunderstorm could have the potential to produce isolated higher amounts due to weak steering winds aloft. Due to these weak steering winds, a low chance will remain in place for isolated heavy rainfall this afternoon and evening, favoring areas along the foothills and southeastern portions of the District at this time. Skies gradually clear through the overnight and into daybreak Sunday. Mild and dry conditions are expected after 10pm and into Sunday as overnight lows drop to around 50 degrees for the plains with mid to upper 40’s along the foothills. STORM RAINFALL POTENTIAL AND DURATION: Typical rain showers will produce rainfall amounts of TR-0.2” in 10-30 minutes. A weak thunderstorm will produce rainfall rates of 0.2-0.5” in 10-30 minutes. WORST CASE SCENARIO: A moderate to strong, slow moving or nearly stationary thunderstorm has the potential to produce heavy rainfall of up to 1.0” in 45-60 minutes. A LOOK AHEAD: Similar conditions remain in place Sunday, however, drier air aloft should limit the chance for any heavy rainfall. Not much change Monday, with another chance for afternoon/eve rain showers and isolated thunderstorms. A better chance for impactful rain showers/thunderstorms Tuesday with a slight chance of severe weather in the afternoon and evening including large hail, gusty winds and heavy rainfall leading to localized flash flooding. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 900 PM Trace (50%) to 0.2" (25%) to 0.5" (10%) LOW Arapahoe 300 PM TO 900 PM Trace (60%) to 0.2" (30%) to 0.5" (20%) LOW Boulder 300 PM TO 900 PM Trace (50%) to 0.2" (25%) to 0.5" (10%) LOW Broomfield 300 PM TO 900 PM Trace (50%) to 0.2" (25%) to 0.5" (10%) LOW Denver 300 PM TO 900 PM Trace (50%) to 0.2" (25%) to 0.5" (10%) LOW Douglas 300 PM TO 900 PM Trace (60%) to 0.2" (30%) to 0.5" (20%) LOW Jefferson 300 PM TO 900 PM Trace (60%) to 0.2" (30%) to 0.5" (20%) LOW Foothills above 6500ft       Boulder 200 PM TO 800 PM Trace (75%) to 0.2" (50%) to 0.5" (25%) LOW Douglas 200 PM TO 800 PM Trace (75%) to 0.2" (50%) to 0.5" (25%) LOW Jefferson 200 PM TO 800 PM Trace (75%) to 0.2" (50%) to 0.5" (25%) 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]