Flash Flood Prediction Program

Time: 408 PM Tue April 27, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S CONTINUE VALID FOR PORTIONS OF THE DISTRICT - Message 1's issued earlier for Adams, Arapahoe/Aurora, Denver/DIA, and Douglas Counties will remain valid until 8pm this evening. - The strongest thunderstorm activity has exited the District and remained well E of I-25 with weaker rain showers and isolated thunderstorms currently in/around the District. A stronger storm cannot be ruled out over the next few hours before the convective nature of the showers becomes more stratiform and a widespread rain develops this evening. - Rain will be changing over to snow in the foothills above 8,000' by sunset and the snow line will slowly lower to around 6,000' by tomorrow morning, possibly as low as 5,000' briefly. As temperatures cool this evening and a more "upslope" flow develops the rain will be widespread but light to moderate resulting in minor runoff but no flash flood threat exists. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will have the potential to produce 0.1-0.5" of rain in 10-30 minutes. Briefly strong thunderstorms will have the potential to produce 0.3-0.9" of rain in 10-30 minutes. Steady moderate to heavy non-thunderstorm rain may produce 0.4-1.2" in 45-75 minutes early this evening. WORST CASE SCENARIO: Training of thunderstorm cells may produce up to 1.4" in 45-75 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Douglas County 1 Current TO 800 PM Current TO 600 PM Adams County 1 Current TO 800 PM Current TO 600 PM Denver County 1 Current TO 800 PM Current TO 600 PM DIA 1 Current TO 800 PM Current TO 600 PM Arapahoe County 1 Current TO 800 PM Current TO 600 PM the City of Aurora 1 Current TO 800 PM Current TO 600 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 60-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 800 PM TUE 0.1" (100%) to 0.4" (60%) to 1.0" (15%) ISSUED Arapahoe Current TO 800 PM TUE 0.1" (100%) to 0.4" (60%) to 1.0" (15%) ISSUED Boulder Current TO 800 PM TUE 0.1" (100%) to 0.4" (60%) to 1.0" (15%) LOW Broomfield Current TO 800 PM TUE 0.1" (100%) to 0.4" (60%) to 1.0" (15%) LOW Denver Current TO 800 PM TUE 0.1" (100%) to 0.4" (60%) to 1.0" (15%) ISSUED Douglas Current TO 800 PM TUE 0.1" (100%) to 0.4" (60%) to 1.0" (15%) ISSUED Jefferson Current TO 800 PM TUE 0.1" (100%) to 0.4" (60%) to 1.0" (15%) LOW Foothills above 6500ft       Boulder Current TO 800 PM TUE 0.1" (100%) to 0.4" (50%) to 1.0" (5%) NONE Douglas Current TO 800 PM TUE 0.1" (100%) to 0.4" (50%) to 1.0" (5%) NONE Jefferson Current TO 800 PM TUE 0.1" (100%) to 0.4" (50%) to 1.0" (5%) 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]