Time: 912 AM Fri June 25, 2021 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- COOL AGAIN TODAY WITH A GOOD CHANCE FOR AFTERNOON & EVENING THUNDERSTORMS - Cooler temperatures once again today as highs reach the low to mid 70's for the District this afternoon. An abundance of surface moisture this morning with dew points in the low to mid 50's will remain in place as a disturbance moves into the region around midday. This disturbance will tap into some mid to upper-level moisture resulting in a high chance for heavy rainfall this afternoon, along with a moderate chance for severe storms. - Initial storm development will take place over the higher terrain and push out onto the plains between 12-2pm this afternoon. Multiple rounds of storms are likely this afternoon and through the evening with rain showers possible through the overnight and into early morning Saturday before a lull in shower activity during the day Saturday. Storm motions today will start off relatively brisk between 10-15mph. As storms strengthen through the afternoon, outflow boundaries will initiate additional storms which have the potential to remain in place for several minutes bringing an increase chance for longer duration heavy rainfall leading to isolated areas of minor flooding. Best chance for heavy rainfall will be from 2pm until midnight, with light to moderate rainfall after midnight at this time. - Storms may also become severe this afternoon and evening, favoring eastern portions of the District. Strong to severe storms will bring wind gust above 60mph and hail 1" or greater, along with frequent lightning. STORM RAINFALL POTENTIAL AND DURATION: Moderate to strong thunderstorms will have the potential to produce 0.2-0.6" in 10-30 minutes. A strong to severe storm will have the potential to produce 1.2" in 10-30 minutes. WORST CASE SCENARIO: An anchored strong thunderstorm or training of strong thunderstorms will have the potential to produce 2.5" in 60-90 minutes. A LOOK AHEAD: This active pattern will remain in place through the weekend with off and on rainfall chances. Temperatures will play a big role as to whether Colorado receives just widespread off an on rain showers or a mix of rain and isolated thunderstorms. If temperatures remain in the upper 60's to low 70's with adequate cloud cover, the likely outcome will be off and on rain, however, it will only take a couple of hours of sunshine to heat the surface resulting in a better chance for thunderstorms, which will also increase the threat for heavy rainfall. Monday will begin to dry out slightly, with a chance for typical afternoon June showers/isolated thunderstorms. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1159 PM 0.2" (90%) to 0.6" (50%) to 1.2" (25%) HIGH Arapahoe 200 PM TO 1159 PM 0.2" (90%) to 0.6" (50%) to 1.2" (25%) HIGH Boulder 200 PM TO 1159 PM 0.2" (80%) to 0.6" (40%) to 1.2" (20%) HIGH Broomfield 200 PM TO 1159 PM 0.2" (80%) to 0.6" (40%) to 1.2" (20%) HIGH Denver 200 PM TO 1159 PM 0.2" (80%) to 0.6" (40%) to 1.2" (20%) HIGH Douglas 200 PM TO 1159 PM 0.2" (90%) to 0.6" (50%) to 1.2" (25%) HIGH Jefferson 200 PM TO 1159 PM 0.2" (80%) to 0.6" (40%) to 1.2" (20%) HIGH Foothills above 6500ft       Boulder 100 PM TO 1159 PM 0.2" (80%) to 0.6" (40%) to 1.2" (20%) HIGH Douglas 100 PM TO 1159 PM 0.2" (80%) to 0.6" (40%) to 1.2" (20%) HIGH Jefferson 100 PM TO 1159 PM 0.2" (80%) to 0.6" (40%) to 1.2" (20%) 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]