Flash Flood Prediction Program

Time: 934 AM Wed July 19, 2023 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORM ACTIVITY EXPECTED TO INCREASE THIS AFTERNOON AND CONTINUE POSSIBLE INTO THE OVERNIGHT PERIOD Thunderstorms are expected to be more numerous today and a little stronger in and around the District with the aid of an upper level disturbance and an increase in surface moisture. The upper level disturbance will keep rain shower and thunderstorm chances persisting past sunset into the overnight period. Temperatures will be cooler with afternoon highs topping out in the mid 80’s to around 90 over the plains with 70’s in the foothills as a weak cold front will move through. Normal high for Denver today is 91 degrees. Showers and thunderstorms are expected to initiate ahead of noon over the foothills with best chances for thunderstorms over the plains between noon and 10pm. Typical storms will be relatively fast moving from W to E at 20-25mph helping to reduce point rainfall amounts from a single storm resulting in brief light to moderate rain from most storms. Multiple rounds of showers and thunderstorms are expected from early afternoon through late evening. Strong thunderstorms should they develop will be capable of producing brief heavy rainfall. Training of thunderstorm cells could be the culprit for extended periods of heavy rainfall. After 10pm the chances for showers and thunderstorms will begin to decrease but remain possible beyond midnight into early morning Thursday. Heavy rainfall is not expected overnight but cannot be completely ruled out as moisture will be on the increase at the surface and aloft. STORM RAINFALL POTENTIAL AND DURATION: Weak thunderstorms will produce a 0.1-0.4” of rain. Moderate to strong thunderstorms will have the potential to produce rainfall rates of 0.4-1.0” in 10-30 minutes. WORST CASE SCENARIO: Training of moderate to strong thunderstorm cells may result in up to 1.8” of rain in 45-75 minutes. A LOOK AHEAD: Thunderstorm activity is expected to peak on Thursday with widespread to numerous showers and thunderstorms. Stronger storms will be very capable of producing heavy rainfall that may lead to excessive runoff and possibly flash flooding. Strong storms may also produce severe weather with large hail and gusty winds being the greatest threats. Temperatures will continue to drop with afternoon highs in the upper 70’s to lower 80’s over the plains. Lesser chances for thunderstorms on Friday with temperatures remaining below seasonal averages. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 1200 PM TO 1000 PM 0.1" (70%) to 0.4" (40%) to 1" (15%) MOD Arapahoe 1200 PM TO 1000 PM 0.1" (70%) to 0.4" (40%) to 1" (15%) MOD Boulder 1200 PM TO 1000 PM 0.1" (70%) to 0.4" (40%) to 1" (15%) MOD Broomfield 1200 PM TO 1000 PM 0.1" (70%) to 0.4" (40%) to 1" (15%) MOD Denver 1200 PM TO 1000 PM 0.1" (70%) to 0.4" (40%) to 1" (15%) MOD Douglas 1200 PM TO 1000 PM 0.1" (70%) to 0.4" (40%) to 1" (15%) MOD Jefferson 1200 PM TO 1000 PM 0.1" (70%) to 0.4" (40%) to 1" (15%) MOD Foothills above 6500ft       Boulder 1100 AM TO 1000 PM 0.1" (80%) to 0.4" (40%) to 1" (10%) LOW Douglas 1100 AM TO 1000 PM 0.1" (80%) to 0.4" (40%) to 1" (10%) LOW Jefferson 1100 AM TO 1000 PM 0.1" (80%) to 0.4" (40%) to 1" (10%) 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]