Flash Flood Prediction Program

Time: 905 AM Mon August 15, 2022 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORMS VERY CAPABLE OF PRODUCING HEAVY RAINFALL THAT MAY LEAD TO EXCESSIVE RUNOFF AND FLASH FLOODING - An upper level disturbance will move through the state today and focus monsoon moisture over the District leading to thunderstorms very capable of producing heavy rainfall that may lead to excessive runoff and possibly flash flooding. The NWS in Boulder has issued a Flood Watch/Flash Flood Watch for Boulder, Jefferson and Douglas Counties above 6,000ft from 1pm to midnight. Other Counties not within the watch have a similar threat for heavy rainfall and Message 1's/2's will be issued by around noon. - Thunderstorms will first develop over the mountains and foothills between 11am and noon. Thunderstorms will become possible over the adjacent plains between noon-2pm. Numerous showers and thunderstorms or multiple rounds of showers and thunderstorms are expected into the evening. Moderate to strong thunderstorms will be very capable of producing heavy rainfall. After 10 or 11pm the threat for thunder diminishes with additional rain showers overnight into early Tuesday morning. - Upper level steering winds will generally be from W to E between 10-20mph helping to keep the storms moving along and the heavy rainfall relatively brief. The greatest threats for extended periods of heavy rainfall today will be from training of thunderstorm cells or a large, slower moving thunderstorm. The first or second round of storms will likely be the strongest of the day but subsequent storms will be very efficient rainfall producers and even weak thunderstorms will be capable of producing heavy rain. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce rainfall rates of 0.3-0.8" in 10-30 minutes. Strong thunderstorms will have the potential to produce heavy rainfall rates of 0.8-2.2" in 10-30 minutes. WORST CASE SCENARIO: Training of thunderstorm cells or a large/slower moving thunderstorm may produce up to 3.5" of rain in 45-60 minutes. A LOOK AHEAD: Lingering rain showers may persist past daybreak on Tuesday with the best chances for afternoon thunderstorms being suppressed S and W leaving the majority of the District with isolated afternoon thunderstorms. If temperatures trend too cool conditions may end up being on the drier side. With ample moisture still in place if thunderstorms do develop Tuesday afternoon they will be capable of producing heavy rain. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 100 PM TO 1159 PM 0.5" (80%) to 1.3" (60%) to 2.0" (30%) HIGH Arapahoe 100 PM TO 1159 PM 0.5" (80%) to 1.3" (60%) to 2.0" (30%) HIGH Boulder 100 PM TO 1159 PM 0.5" (90%) to 1.3" (60%) to 2.0" (30%) HIGH Broomfield 100 PM TO 1159 PM 0.5" (80%) to 1.3" (60%) to 2.0" (30%) HIGH Denver 100 PM TO 1159 PM 0.5" (80%) to 1.3" (60%) to 2.0" (30%) HIGH Douglas 100 PM TO 1159 PM 0.5" (90%) to 1.3" (60%) to 2.0" (30%) HIGH Jefferson 100 PM TO 1159 PM 0.5" (90%) to 1.3" (60%) to 2.0" (30%) HIGH Foothills above 6500ft       Boulder 1200 PM TO 1159 PM 0.5" (95%) to 1.3" (65%) to 2.0" (30%) HIGH Douglas 1200 PM TO 1159 PM 0.5" (95%) to 1.3" (65%) to 2.0" (30%) HIGH Jefferson 1200 PM TO 1159 PM 0.5" (95%) to 1.3" (65%) to 2.0" (30%) 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]