Time: 903 AM Thu June 8, 2023 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- 1-2 ROUNDS OF AFTERNOON/EVENING SHOWERS/THUNDERSTORMS, BRIEF HEAVY RAIN REMAINS A THREAT Temperatures will continue to run slightly below seasonal averages over the District today with afternoon highs climbing into the upper 70’s to around 80. Normal high for Denver today is 81 degrees. Mostly sunny skies this morning will become mostly cloudy to cloudy this afternoon and early evening. Some slight changes in the weather pattern today but it will not change our chances for thunderstorms much, it will just result in storms moving in a different direction. Yesterday the upper level flow was from SE to NW, today upper level winds will be more SW to NE allowing storms that form over the foothills to move onto the plains. Thunderstorms will develop over the foothills between noon and 2pm. Chances for thunderstorms spread out onto the plains between 2-3pm with prime time from 2pm to 8 or 9pm. 1-2 rounds of thunderstorms are expected through the afternoon with additional isolated light rain showers possible after 9pm through roughly midnight. Moisture levels remain robust in and around the District resulting in stronger thunderstorms capable of producing brief heavy rainfall and possibly hail. Best chances for stronger storms today appears to be over the foothills and S of I-70 but the presence of outflow boundaries may help spread the stronger storm activity to other areas as well. Increased storm motions today from SW to NE at 15-20mph will help to lower point rainfall amounts slightly and extended periods of heavy rain is not expected but brief heavy rain is likely. A stalled out strong thunderstorm along a wind convergence line or training of thunderstorm cells will be the likely culprits for extended periods of heavy rain. STORM RAINFALL POTENTIAL AND DURATION: Weak thunderstorms will produce rainfall amounts of 0.1-0.4”. Moderate to strong thunderstorms will produce rainfall rates of 0.4-1.1” in 10-30 minutes. WORST CASE SCENARIO: A slower moving strong thunderstorm or training of thunderstorm cells may result in up to 1.8” of rain in 45-60 minutes. A LOOK AHEAD: A slight decrease in thunderstorm activity is expected on Friday but there will still be a modest chance for stronger storms with the potential for heavy rainfall. A cold front will move through on Saturday and result in an uptick in thunderstorm coverage and stronger storms will be more likely. Cooler Sunday in the 60’s for afternoon highs with scattered to numerous rain showers and embedded thunderstorms. Thunderstorms will continue to have the potential to produce heavy rainfall through the upcoming weekend which may lead to excessive runoff and possibly flash flooding. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 800 PM 0.1" (75%) to 0.4" (40%) to 1.1" (15%) MOD Arapahoe 200 PM TO 800 PM 0.1" (80%) to 0.4" (50%) to 1.1" (20%) HIGH Boulder 200 PM TO 800 PM 0.1" (75%) to 0.4" (40%) to 1.1" (15%) MOD Broomfield 200 PM TO 800 PM 0.1" (75%) to 0.4" (40%) to 1.1" (15%) MOD Denver 200 PM TO 800 PM 0.1" (80%) to 0.4" (50%) to 1.1" (20%) HIGH Douglas 200 PM TO 800 PM 0.1" (90%) to 0.4" (60%) to 1.1" (25%) HIGH Jefferson 200 PM TO 800 PM 0.1" (80%) to 0.4" (50%) to 1.1" (20%) HIGH Foothills above 6500ft       Boulder 100 PM TO 800 PM 0.1" (85%) to 0.4" (50%) to 1.1" (20%) HIGH Douglas 100 PM TO 800 PM 0.1" (95%) to 0.4" (60%) to 1.1" (25%) HIGH Jefferson 100 PM TO 800 PM 0.1" (90%) to 0.4" (55%) to 1.1" (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]