Time: 1017 AM Sun July 21, 2024 Forecaster: Laura Smith ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- Cool with scattered to numerous showers and thunderstorms throughout most of day Northeasterly upslope flow throughout the morning and early afternoon will spark convection over the high country outside the District sometime before Noon today. By the time this activity reaches the District, forecasted precipitable water (PWAT) values of 1.00" and dewpoints around 50 indicate that any storm could be capable of producing rainfall worthy of message issuance. This convection will spread to the foothills including areas in and around the District by midafternoon, and reach the plains shortly thereafter. Cooler temperatures today may keep overall convective behavior slightly stunted, but rainfall still has potential to be significant in isolated cases. Storms will move from NW to SE at 10-20mph, and continued upslope flow through sunset will keep these showers in the general area through the evening, with the potential for isolated light showers through the late evening. STORM RAINFALL POTENTIAL AND DURATION: Typical showers and thunderstorms will produce 0.30"-0.60" in 15-30 minutes. Stronger/slower moving storms will produce up to 1.25" in 30 minutes. WORST CASE SCENARIO: A strong/stationary thunderstorm or a training of heavy showers may produce 2.00" in 30 minutes or less. A LOOK AHEAD: The southwestern US ridge starts to build back into Colorado starting Monday, bringing with it a warmer and drier airmass. This will decrease thunderstorm coverage to isolated/scattered Monday, then isolated Tuesday and Wednesday, with temperatures reaching the 90s again by Wednesday. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM 0.3" (75%) to 0.6" (50%) to 1.25" (25%) HIGH Arapahoe 200 PM TO 1000 PM 0.3" (75%) to 0.6" (50%) to 1.25" (25%) HIGH Boulder 200 PM TO 1000 PM 0.3" (75%) to 0.6" (50%) to 1.25" (25%) HIGH Broomfield 200 PM TO 1000 PM 0.3" (75%) to 0.6" (50%) to 1.25" (25%) HIGH Denver 200 PM TO 1000 PM 0.3" (75%) to 0.6" (50%) to 1.25" (25%) HIGH Douglas 200 PM TO 1000 PM 0.3" (80%) to 0.6" (60%) to 1.25" (40%) HIGH Jefferson 200 PM TO 1000 PM 0.3" (80%) to 0.6" (60%) to 1.25" (40%) HIGH Foothills above 6500ft       Boulder 100 PM TO 1000 PM 0.3" (80%) to 0.6" (60%) to 1.25" (40%) HIGH Douglas 100 PM TO 1000 PM 0.3" (80%) to 0.6" (60%) to 1.25" (40%) HIGH Jefferson 100 PM TO 1000 PM 0.3" (80%) to 0.6" (60%) to 1.25" (40%) 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]