Time: 1001 AM Sun July 24, 2022 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- MULTIPLE ROUNDS OF HEAVY RAINFALL PRODUCING THUNDERSTORMS/EXCESSIVE RUNOFF LIKELY - All the ingredients are in place today for multiple rounds of heavy rainfall producing thunderstorms. The NWS has issued a Flash Flood Watch for Boulder County above 6,000ft as well as a Flood Watch for the E 2/3's of Douglas County above 6,000ft. The Flood Watch will be treated as a Flash Flood Watch as it implies flash flooding resulting in Message 2's being issued for Boulder and Douglas Counties from 3pm to midnight to sync with the NWS. Message 1's will be issued for all Counties prior to 3pm and then the Message 1's will transition to Message 2's for Boulder and Douglas Counties. The Message 2's may be cancelled by the NWS prior to midnight and the current thinking is that this may occur around 9 or 10pm. - Thunderstorms will first initiate over the mountains and foothills W of the District between 11am and noon. Upper level steering winds from W to E at 15-20mph will push the storms eastward onto the plains between noon and 1 or 2pm. Prime time for wetting rain showers and moderate to strong thunderstorms will be from 1pm to 10pm. Multiple rounds (2-3) of storms are expected through the afternoon into the early evening. - Moderate to strong thunderstorms that develop today will be efficient rainfall producers as moisture levels are very high for Colorado standards. Even moderate thunderstorms will have the potential to produce heavy rainfall and strong thunderstorms will be very capable of producing heavy downpours that may lead to excessive runoff and flash flooding. STORM RAINFALL POTENTIAL AND DURATION: Weak thunderstorms will produce 0.3-0.8" in 10-30 minutes. Moderate to strong thunderstorms will have the potential to produce 0.8-2.0 in 10-30 minutes. WORST CASE SCENARIO: A large thunderstorm complex or a slower moving large thunderstorm may result in rainfall rates of 1.0-2.5" in 10-30 minutes and up to 3.5" in 45-75 minutes. A LOOK AHEAD: Drier air will filter in from the NW on Monday pushing the best chances for strong thunderstorms to the S and E of the District. There will still be ample moisture in place at the surface to fuel storms but the coverage will be isolated favoring the Palmer Divide and eastern plains with a lower flood threat overall. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Arapahoe 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Boulder 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Broomfield 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (25%) HIGH Denver 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Douglas 100 PM TO 1000 PM 0.2" (95%) to 0.8" (75%) to 2.0" (30%) HIGH Jefferson 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Foothills above 6500ft       Boulder 1200 PM TO 1000 PM 0.2" (100%) to 0.8" (75%) to 2.0" (25%) HIGH Douglas 1200 PM TO 1000 PM 0.2" (100%) to 0.8" (75%) to 2.0" (25%) HIGH Jefferson 1200 PM TO 1000 PM 0.2" (100%) to 0.8" (75%) to 2.0" (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]