Time: 1230 PM Sun June 13, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORM CHANCES INCREASING AS MOISTURE LEVELS REMAIN ELEVATED ALONG THE I-25 CORRIDOR - A boom or bust thunderstorm forecast remains in place today as easterly winds are keeping surface moisture elevated along the I-25 corridor with dew points currently in the low 50's to lower 60's. A warm layer of air aloft will need to be overcome in order to tap into the rich surface moisture as fuel for thunderstorms. There remains a high amount of uncertainty as to whether or not all the ingredients will come together just right for storms today but if they form they will become strong/severe. - Daytime heating alone is likely not be enough to overcome the stable/warm layer aloft but outflow boundaries from thunderstorms outside the District could be the trigger needed for thunderstorm initiation within District boundaries. Thunderstorms are currently building south along the crest of the Palmer Divide and these initial storms will have the potential to produce a rain cooled outflow/gust front that may move northward over the coming hours. - If temperatures warm enough to initiate convection or if a thunderstorm outflow boundary moves into the District Message 1's may need to be issued. The next few hours will be telling on how the rest of the afternoon will play out. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce a trace to 0.3" of rain. Strong thunderstorms will have the potential to produce 0.3-0.9" of rain in 10-30 minutes. WORST CASE SCENARIO: Moisture levels remain elevated with strong/slow moving thunderstorms having the potential to produce up to 1.8" in 45-60 minutes. A LOOK AHEAD: The heat wave intensifies on Tuesday with temperatures reaching the mid 90's to around 100 degrees over the plains. Temperatures will peak on Tuesday in the upper 90's to lower 100's. Dry conditions are expected both days. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 900 PM Trace (60%) to 0.3" (30%) to 0.8" (15%) MOD Arapahoe 300 PM TO 900 PM Trace (60%) to 0.3" (30%) to 0.8" (15%) MOD Boulder 300 PM TO 900 PM Trace (60%) to 0.3" (30%) to 0.8" (15%) MOD Broomfield 300 PM TO 900 PM Trace (60%) to 0.3" (30%) to 0.8" (15%) MOD Denver 300 PM TO 900 PM Trace (60%) to 0.3" (30%) to 0.8" (15%) MOD Douglas 300 PM TO 900 PM Trace (80%) to 0.3" (40%) to 0.8" (15%) MOD Jefferson 300 PM TO 900 PM Trace (75%) to 0.3" (35%) to 0.8" (15%) MOD Foothills above 6500ft       Boulder 100 PM TO 900 PM Trace (80%) to 0.3" (40%) to 0.8" (15%) MOD Douglas 100 PM TO 900 PM Trace (90%) to 0.3" (40%) to 0.8" (15%) MOD Jefferson 100 PM TO 900 PM Trace (90%) to 0.3" (40%) to 0.8" (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]