Flash Flood Prediction Program

Time: 913 AM Tue July 13, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORM ACTIVITY RETURNS TO THE DISTRICT - Hazy conditions continue to impact visibility today with temperatures warming into the upper 80's to lower 90's over the plains and upper 70's to 80's in the Front Range foothills. Mid and upper level moisture is on the increase and will lead to a return of thunderstorm activity over the District. - Surface moisture is only modest at best and will result in the storms that develop today generally producing light rain and gusty winds over the plains. The foothills stand a better chance for a stronger storm to produce brief moderate rain. An isolated sprinkle cannot be ruled this morning with thunderstorms developing over the higher terrain by around noon. By early afternoon chances for thunderstorms will spread out onto the plains. Isolated to widely scattered thunderstorm coverage is expected through the afternoon and may linger until around 10pm this evening. - Upper level steering winds responsible for importing the smoke but will also steer storms is from NW to SE at around 20mph. Individual thunderstorms will be relatively fast moving with training of thunderstorm cells or a briefly anchored thunderstorm possibly producing an extended period of moderate rain. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.1" of rain. Moderate and briefly strong thunderstorms will have the potential to produce 0.1-0.4" of rain in 10-30 minutes. WORST CASE SCENARIO: Training of thunderstorm cells or a briefly anchored strong thunderstorm may result in 0.3-0.8" of rain in 15-45 minutes. A LOOK AHEAD: A cold front will move through on Wednesday and lower temperatures into the 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 Trace (80%) to 0.2" (40%) to 0.4" (10%) NONE Arapahoe 200 PM TO 1000 PM Trace (80%) to 0.2" (40%) to 0.4" (10%) NONE Boulder 200 PM TO 1000 PM Trace (90%) to 0.2" (60%) to 0.4" (15%) NONE Broomfield 200 PM TO 1000 PM Trace (80%) to 0.2" (40%) to 0.4" (10%) NONE Denver 200 PM TO 1000 PM Trace (80%) to 0.2" (40%) to 0.4" (10%) NONE Douglas 200 PM TO 1000 PM Trace (90%) to 0.2" (60%) to 0.4" (15%) NONE Jefferson 200 PM TO 1000 PM Trace (90%) to 0.2" (60%) to 0.4" (15%) NONE Foothills above 6500ft       Boulder 100 PM TO 1000 PM Trace (100%) to 0.2" (75%) to 0.4" (25%) NONE Douglas 100 PM TO 1000 PM Trace (100%) to 0.2" (75%) to 0.4" (25%) NONE Jefferson 100 PM TO 1000 PM Trace (100%) to 0.2" (75%) to 0.4" (25%) 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]