Flash Flood Prediction Program

Time: 855 AM Tue August 3, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- RAIN SHOWERS AND THUNDERSTORMS RETURN TOTHE DISTRICT - Plume of moisture to the west yesterday will move overhead today along with a passing upper level disturbance resulting in rain showers and thunderstorms returning to the District. Showers are already ongoing over portions of Jefferson and Boulder Counties and any shower activity this morning will favor the higher terrain. - Thunderstorms will develop by around noon over the foothills and slowly begin to develop over the plains between 2-4pm. Best chances for thunderstorms will be from 4-10pm with lingering rain showers likely until midnight or shortly after. Cloud cover may limit heating and in turn may keep thunderstorms more weak to moderate today? Moderate to strong thunderstorms will be capable of producing heavy rainfall that may lead to excessive runoff and possibly flash flooding. - The foothills and Palmer Divide are expected to experience the more numerous storms than the plains but the stronger thunderstorm activity may favor S/SE areas of the District where there is expected to be a bit more sunshine through the first half of the day. Showers and thunderstorms will be slow moving and result in extended periods of moderate and heavy rainfall. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce 0.1-0.5" in 10-30 minutes. Moderate to strong thunderstorms will have the potential to produce 0.5-1.5" of heavy rain in 10-30 minutes. WORST CASE SCENARIO: A stationary strong thunderstorm may result in up to 2.5" in 45-60 minutes. A LOOK AHEAD: Moisture remains in place on Wednesday but begins to decrease with less numerous showers and thunderstorms compared to today. Widely scattered thunderstorm coverage is expected in the afternoon with a lower threat for heavy rainfall. Thursday is trending dry at this time. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 400 PM TO 1000 PM 0.1" (90%) to 0.5" (40%) to 1.5" (20%) HIGH Arapahoe 400 PM TO 1000 PM 0.1" (95%) to 0.5" (60%) to 1.5" (30%) HIGH Broomfield 400 PM TO 1000 PM 0.1" (90%) to 0.5" (40%) to 1.5" (20%) HIGH Denver 400 PM TO 1000 PM 0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH Boulder 300 PM TO 1000 PM 0.1" (95%) to 0.5" (60%) to 1.5" (30%) HIGH Douglas 300 PM TO 1000 PM 0.1" (95%) to 0.5" (60%) to 1.5" (30%) HIGH Jefferson 300 PM TO 1000 PM 0.1" (95%) to 0.5" (60%) to 1.5" (30%) HIGH Foothills above 6500ft       Boulder 100 PM TO 1000 PM 0.1" (100%) to 0.5" (75%) to 1.5" (25%) HIGH Douglas 100 PM TO 1000 PM 0.1" (100%) to 0.5" (75%) to 1.5" (25%) HIGH Jefferson 100 PM TO 1000 PM 0.1" (100%) to 0.5" (75%) to 1.5" (25%) HIGH MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]