Flash Flood Prediction Program

Time: 1135 AM Tue July 13, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORM ACTIVITY RETURNS TO THE DISTRICT/BRIEF HEAVY RAINFALL POSSIBLE - A pseudo cold front moved through this morning and will likely keep temperatures a little cooler than expected in the 80's for highs over the plains. Behind this feature surface moisture has increased and will result in a better chance for thunderstorms this afternoon to produce brief heavy rainfall. - Thunderstorms are beginning to develop to the SW of the District currently and will become possible over the plains by early afternoon. NW to SE upper level winds at 15-20mph will keep storms moving along with any moderate to heavy rainfall being brief. Prime time for thunderstorms will be 2-9pm with the best chances for stronger storms over the W and S portions of the District. Training of thunderstorm cells or a briefly anchored thunderstorm will be the likely culprits for extended periods of moderate/heavy rain. - After 9 or 10pm any thunderstorm activity is expected to have diminished. Lingering isolated to widely scattered rain showers remain possible until midnight. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce 0.1-0.3" of rain. Moderate and briefly strong thunderstorms will have the potential to produce 0.3-0.8" of rain in 10-30 minutes. WORST CASE SCENARIO: Training of thunderstorm cells or a briefly anchored strong thunderstorm may result in up to 1.5" of rain in 45-60 minutes. A LOOK AHEAD: A cold front will move through on Wednesday and lower temperatures into the low and mid 80's for highs over the plains. The front will increase surface moisture and result in stronger thunderstorms capable of producing heavy rainfall that may lead to excessive runoff. Scattered to numerous storms are expected with chances extending well into the evening Wednesday. Stronger storms may also become severe with large hail and gusty winds being the primary threats. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM 0.1" (60%) to 0.3" (30%) to 0.8" (10%) LOW Arapahoe 200 PM TO 1000 PM 0.1" (60%) to 0.3" (30%) to 0.8" (10%) LOW Boulder 200 PM TO 1000 PM 0.1" (80%) to 0.3" (40%) to 0.8" (20%) MOD Broomfield 200 PM TO 1000 PM 0.1" (60%) to 0.3" (30%) to 0.8" (10%) LOW Denver 200 PM TO 1000 PM 0.1" (60%) to 0.3" (30%) to 0.8" (10%) LOW Douglas 200 PM TO 1000 PM 0.1" (80%) to 0.3" (40%) to 0.8" (20%) MOD Jefferson 200 PM TO 1000 PM 0.1" (80%) to 0.3" (40%) to 0.8" (20%) MOD Foothills above 6500ft       Boulder 1200 PM TO 1000 PM 0.1" (90%) to 0.3" (60%) to 0.8" (30%) MOD Douglas 1200 PM TO 1000 PM 0.1" (90%) to 0.3" (60%) to 0.8" (30%) MOD Jefferson 1200 PM TO 1000 PM 0.1" (90%) to 0.3" (60%) to 0.8" (30%) MOD MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]