Flash Flood Prediction Program

Time: 857 AM Wed September 21, 2022 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- COOLER, CLOUDY WITH RAIN SHOWERS ON THE INCREASE AS THE DAY PROGRESSES - Much cooler and cloudy today as a cold front moved through overnight. Official highs for the date were likely reached just after midnight last night with readings through the day mainly in the 50's to around 60. Conditions will be generally dry through the morning with possibly a few small areas of light showers or mist/drizzle. - Rain showers will begin to fill in this afternoon becoming widespread by late afternoon or early evening. Precipitation is expected to be a stratiform rain versus convective thunderstorms resulting in mainly light to moderate rain but if a thunderstorm is observed brief heavy rainfall will be possible. - Prime time for rain showers will be starting between 2-4pm and continue through Thursday morning. Upslope flow at the surface will favor areas in and near the foothills for more persistent showers and higher rainfall totals into Thursday morning. Typical rainfall amounts from midday today until Thursday morning is expected to range from 0.25-0.75" with isolated higher amounts. STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce rainfall rates of trace to 0.3" in 30-60 minutes. WORST CASE SCENARIO: A thunderstorm is able to develop with the potential to produce brief heavy rainfall of 0.3-0.8" in 10-30 minutes. Although unlikely, this threat will result in a LOW Message potential today. A LOOK AHEAD: Rain showers will continue into Thursday morning with some lulls at times through the day. Precipitation will begin to move out of the District during the mid to late afternoon and conditions will dry out in the evening hours. Highs Thursday only in the 50's foothills with some 60's over the plains. LOCATION PRIME TIME 60-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 AM THU Trace (100%) to 0.1" (75%) to 0.3" (50%) LOW Arapahoe 200 PM TO 1000 AM THU Trace (100%) to 0.1" (75%) to 0.3" (50%) LOW Boulder 200 PM TO 1000 AM THU Trace (100%) to 0.1" (75%) to 0.3" (50%) LOW Broomfield 200 PM TO 1000 AM THU Trace (100%) to 0.1" (75%) to 0.3" (50%) LOW Denver 200 PM TO 1000 AM THU Trace (100%) to 0.1" (75%) to 0.3" (50%) LOW Douglas 200 PM TO 1000 AM THU Trace (100%) to 0.1" (75%) to 0.3" (50%) LOW Jefferson 200 PM TO 1000 AM THU Trace (100%) to 0.1" (75%) to 0.3" (50%) LOW Foothills above 6500ft       Boulder 1200 PM TO 1000 AM THU Trace (100%) to 0.1" (80%) to 0.3" (60%) LOW Douglas 1200 PM TO 1000 AM THU Trace (100%) to 0.1" (80%) to 0.3" (60%) LOW Jefferson 1200 PM TO 1000 AM THU Trace (100%) to 0.1" (80%) to 0.3" (60%) 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]