Time: 900 AM Sat July 8, 2023 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- ONE MORE ACTIVE DAY WITH THUNDERSTORMS CONTAINING HEAVY RAINFALL AND HAIL THEN A DRIER WEATHER PATTERN WILL DEVELOP Another active thunderstorm day in and around the District with stronger storms very capable of producing brief heavy rainfall but a drier weather pattern will unfold over the coming days. Temperatures will continue to run below seasonal averages with afternoon highs in the mid 70’s to around 80 over the plains. Normal high for Denver today is 90 degrees. Moisture remains abundant at the surface and aloft today with precipitable water values at or above 1.0” and surface dew points firmly in the 50’s. The available moisture will be fuel for thunderstorms this afternoon and evening with some storms becoming strong to severe producing brief heavy rainfall and hail. Daytime heating will play a factor on when storms develop and exactly where the stronger storms set up remains uncertain but will likely favor areas E of I-25 (but could end up further west towards the base of the foothills). Storms will first initiate over the foothills by around noon and then spread eastward onto the plains between 1-3pm strengthening as they do so. Chances for thunderstorms will continue into the evening with prime time from 2-10pm. After 10pm chances for showers and thunderstorms diminish but remain possible through about midnight. Storm motions are brisk from W to E or WNW to ESE at 20-25mph which will help to reduce point rainfall amounts but large thunderstorms or briefly anchored thunderstorms along surface wind convergence may result in extended periods of heavy rainfall that may lead to excessive runoff and possibly flash flooding. Message 1’s will likely be issued by early afternoon. STORM RAINFALL POTENTIAL AND DURATION: Weak thunderstorms will produce 0.1-0.5” of rain. Moderate to strong thunderstorms will have the potential to produce rainfall rates of 0.5-1.5” in 10-30 minutes. WORST CASE SCENARIO: A large thunderstorm complex or briefly anchored strong thunderstorm may result in up to 2.5” of rain in 45-60 minutes. A LOOK AHEAD: Conditions will begin to dry out on Sunday and Monday with a low chance for isolated afternoon thunderstorms, favoring areas near the foothills and over the Palmer Divide. Temperatures on Sunday warm into the 80’s with low to mid 90’s on Monday over the plains. Tuesday and Wednesday will continue to produce afternoon highs in the 90’s over the plains with plenty of sunshine and dry conditions expected. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM 0.1" (90%) to 0.5" (60%) to 1.5" (30%) HIGH Arapahoe 200 PM TO 1000 PM 0.1" (90%) to 0.5" (60%) to 1.5" (30%) HIGH Broomfield 200 PM TO 1000 PM 0.1" (90%) to 0.5" (50%) to 1.5" (20%) HIGH Denver 200 PM TO 1000 PM 0.1" (90%) to 0.5" (60%) to 1.5" (25%) HIGH Boulder 100 PM TO 1000 PM 0.1" (90%) to 0.5" (60%) to 1.5" (25%) HIGH Douglas 100 PM TO 1000 PM 0.1" (90%) to 0.5" (60%) to 1.5" (30%) HIGH Jefferson 100 PM TO 1000 PM 0.1" (90%) to 0.5" (50%) to 1.5" (20%) HIGH Foothills above 6500ft       Boulder 1200 PM TO 1000 PM 0.1" (90%) to 0.5" (50%) to 1.5" (15%) MOD Douglas 1200 PM TO 1000 PM 0.1" (90%) to 0.5" (50%) to 1.5" (15%) MOD Jefferson 1200 PM TO 1000 PM 0.1" (90%) to 0.5" (50%) to 1.5" (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]