Time: 932 AM Sun May 16, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- CLOUDY AND COOL THIS MORNING WITH AFTERNOON/EVENING RAIN SHOWERS AND THUNDERSTORMS - Low clouds in place over the District this morning will give way to some sunshine into early afternoon southern areas while the clouds may hang around much of the day northward. The clouds and their impact on daytime heating will have repercussions on thunderstorm strength and coverage this afternoon/evening. Highs will remain in the 60's in locations with more persistent cloud cover while southern zones may be able to reach the lower 70's. - Much like yesterday, locations that experience more sun through the first half of the day will have the better chances for stronger thunderstorms in the afternoon. This should trend to better coverage of storms over the foothills and southern portions of the District. However, outflow generated from initial storms may produce gust fronts that can trigger additional storms in the less favorable/cooler environment. If clouds dissipate quickly this morning then storm chances increase across the board. - There are enough favorable ingredients today with modest moisture in place and slower storm motions for strong thunderstorms that develop to have the potential for heavy rainfall that could lead to excessive runoff. Storm motions will generally be from W to E at 10-15mph but stronger storms may anchor or move erratically along gust fronts/outflow boundaries. Best chances for thunderstorms today will be from 1-9pm over the higher terrain and from 3-10pm over the plains. Additional light rain showers remain possible after 10pm. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will have the potential to produce 0.1-0.4" in 10-30 minutes. Strong thunderstorms will have the potential to produce 0.4-1.0" in 10-30 minutes. WORST CASE SCENARIO: An anchored strong thunderstorm or training of thunderstorm cells may result in up to 2.0" of rain in 60 minutes or less. A LOOK AHEAD: Shower and thunderstorm activity is expected to increase on Monday becoming scattered to widespread in the afternoon. Thunderstorm chances decrease Monday evening, transitioning to a soaking non-thunderstorm rain at times overnight into Tuesday morning. Additional rain shower activity is expected through the day on Tuesday with possibly an isolated thunderstorm in the afternoon. Temperatures will continue to trend below seasonal averages. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 1000 PM 0.1" (80%) to 0.4" (40%) to 1.0" (15%) MOD Arapahoe 300 PM TO 1000 PM 0.1" (85%) to 0.4" (50%) to 1.0" (15%) MOD Broomfield 300 PM TO 1000 PM 0.1" (80%) to 0.4" (40%) to 1.0" (15%) MOD Denver 300 PM TO 1000 PM 0.1" (80%) to 0.4" (40%) to 1.0" (15%) MOD Boulder 200 PM TO 1000 PM 0.1" (80%) to 0.4" (40%) to 1.0" (15%) MOD Douglas 200 PM TO 1000 PM 0.1" (90%) to 0.4" (60%) to 1.0" (15%) MOD Jefferson 200 PM TO 1000 PM 0.1" (85%) to 0.4" (50%) to 1.0" (15%) MOD Foothills above 6500ft       Boulder 100 PM TO 900 PM 0.1" (90%) to 0.4" (60%) to 1.0" (15%) MOD Douglas 100 PM TO 900 PM 0.1" (90%) to 0.4" (60%) to 1.0" (15%) MOD Jefferson 100 PM TO 900 PM 0.1" (90%) to 0.4" (60%) to 1.0" (15%) MOD MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]