Flash Flood Prediction Program

Time: 932 AM Sat June 18, 2022 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORM ACTIVITY INCREASES/BRIEF MODERATE TO HEAVY RAINFALL LIKELY - Flow aloft from the S/SW will import subtropical "monsoon" moisture in the mid and upper levels of the atmosphere into the District today resulting in an increase in thunderstorm activity. Temperatures will be held down due to more cloud cover today with highs topping out in the upper 80's to mid 90's over the plains with 70's and 80's in the Front Range foothills. Surface winds will be breezy at times from the S/SE gusting to 20mph or more. - Showers and thunderstorms will be on the increase between 11am and 1pm with best chances for thunderstorm activity through about 10pm then additional rain showers continue possible into the early overnight period. Fast storm motions from SSW to NNE at 25-30mph will help to reduce point rainfall amounts from a single storm, keeping the heavier rains brief in duration. Training of thunderstorm cells over a single point may result in extended periods of moderate to heavy rainfall that may lead to excessive runoff. Stronger thunderstorms may also contain gusty winds, and hail. - Multiple rounds of showers and thunderstorm are likely from early afternoon into the evening. Thunderstorm coverage over the plains is expected to be widely scattered with more numerous storms over the foothills. After 9 or 10pm the threat for thunderstorms diminish with any additional rainfall being on the light side. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.3" 10-30 minutes. Moderate to strong thunderstorms will have the potential to produce rainfall rates of 0.3-0.8" in 10-30 minutes. WORST CASE SCENARIO: Training of thunderstorm cells may result in up to 1.6" of rainfall in 45-75 minutes. A LOOK AHEAD: Another active day on Sunday with monsoon moisture impacting the District leading to scattered afternoon and evening thunderstorms. Storm motions will continue to be fast leading to brief bouts of heavy rainfall. Temperatures will continue to retreat with highs in the 80's to around 90 over the plains. Conditions dry out on Monday but temperatures remain in the 80s to around 90 for afternoon highs. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM Trace (95%) to 0.3" (60%) to 0.8" (15%) MOD Arapahoe 200 PM TO 1000 PM Trace (95%) to 0.3" (60%) to 0.8" (15%) MOD Broomfield 200 PM TO 1000 PM Trace (95%) to 0.3" (60%) to 0.8" (15%) MOD Denver 200 PM TO 1000 PM Trace (95%) to 0.3" (60%) to 0.8" (15%) MOD Boulder 100 PM TO 1000 PM Trace (95%) to 0.3" (60%) to 0.8" (15%) MOD Douglas 100 PM TO 1000 PM Trace (95%) to 0.3" (60%) to 0.8" (15%) MOD Jefferson 100 PM TO 1000 PM Trace (95%) to 0.3" (60%) to 0.8" (15%) MOD Foothills above 6500ft       Boulder 1200 PM TO 1000 PM Trace (100%) to 0.3" (75%) to 0.8" (20%) MOD Douglas 1200 PM TO 1000 PM Trace (100%) to 0.3" (75%) to 0.8" (20%) MOD Jefferson 1200 PM TO 1000 PM Trace (100%) to 0.3" (75%) to 0.8" (20%) 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]