Flash Flood Prediction Program

Time: 845 AM Sun May 21, 2023 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- WARMER TODAY WITH A FEW HIGH-BASED SHOWERS/ISOLATED THUNDERSTORMS ALONG THE HIGHER TERRAIN A weak ridge of high-pressure will build over the region today leading to mostly mild and dry conditions. Hazy skies due to wildfire smoke from Canada will continue to impact the area today and into tomorrow. A few high-based showers/isolated thunderstorms could form along the higher terrain today, onto the foothills and along the Palmer Divide. Similar to yesterday, these storms will likely remain anchored along the foothills and Palmer Divide with minimal impact for areas within the District. A few weak showers could move onto the I-25 corridor today, however most, if not all precipitation will struggle to reach the surface as dew points mix out into the mid 30’s this afternoon. The best chance for shower activity will be this afternoon and early evening between 1-7pm with skies clearing into the evening. Overnight lows will drop to around 50 degrees on the plains with mid 40’s along the foothills. Mild and dry conditions expected through the overnight and into Monday. STORM RAINFALL POTENTIAL AND DURATION: Typical rain showers will produce TR-0.1" in 10-30 minutes. A weak to moderate thunderstorm will have the potential to produce rainfall rates of 0.1-0.3" in 10-30 minutes. WORST CASE SCENARIO: A slow moving or stationary thunderstorm, or training of rain showers/thunderstorms may result in rainfall rates of up to 0.6" in 45-60 minutes. A LOOK AHEAD: Drier conditions remain in place Monday as the small high-pressure ridge holds throughout most of the day as high temperatures reach the mid to upper 70’s. A very slight chance for high-based rain showers/isolated thunderstorms Monday, with storm activity once again favoring the higher terrain. A disturbance moves into the region Tuesday, bringing a better chance for scattered rain showers/isolated thunderstorms in the afternoon and evening, with a very slight chance for heavy rainfall at this time. A better chance for widespread storms Wednesday with a good chance for moderate to heavy rainfall in the afternoon and evening leading to a good chance for some localized flooding. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 700 PM Trace (20%) to 0.1" (10%) to 0.2" (5%) NONE Arapahoe 200 PM TO 700 PM Trace (20%) to 0.1" (10%) to 0.2" (5%) NONE Boulder 200 PM TO 700 PM Trace (20%) to 0.1" (10%) to 0.2" (5%) NONE Broomfield 200 PM TO 700 PM Trace (20%) to 0.1" (10%) to 0.2" (5%) NONE Denver 200 PM TO 700 PM Trace (20%) to 0.1" (10%) to 0.2" (5%) NONE Douglas 200 PM TO 700 PM Trace (30%) to 0.1" (15%) to 0.2" (5%) NONE Jefferson 200 PM TO 700 PM Trace (30%) to 0.1" (15%) to 0.2" (5%) NONE Foothills above 6500ft       Boulder 100 PM TO 600 PM Trace (40%) to 0.1" (20%) to 0.2" (10%) NONE Douglas 100 PM TO 600 PM Trace (40%) to 0.1" (20%) to 0.2" (10%) NONE Jefferson 100 PM TO 600 PM Trace (40%) to 0.1" (20%) to 0.2" (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]