Time: 1022 AM Thu August 26, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORM ACTIVITY RETURNS TO THE DISTRICT - An upper level disturbance will position SW flow over the District today, facilitating an active weather pattern this afternoon and evening. Scattered showers and thunderstorms, capable of producing moderate to briefly heavy rainfall will sweep across the Front Range Urban Corridor between 1pm and 7pm with a second wave possible later in the evening. Prime time for thunderstorm activity is from 2-10pm. - There is some uncertainty to the strength of the storms today as surface moisture is abundant this morning with dew points in the 50's to lower 60's but the higher dew point air is expected to be pushed eastward by early afternoon. If the higher moisture values remain as far W as the I-25 corridor then storms may be stronger than currently anticipated later today. Storms from outside the District may also produce outflow boundaries that push moisture back into the District providing additional fuel for storms resulting in a moderate threat for heavy rainfall. - Thunderstorms will move from SW to NE at around 20mph which will help to limit point rainfall amounts from a single storm. Slower moving storms that develop on outflow boundaries will pose the greatest risk for extended periods of heavy rainfall today. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.3" of rain. Moderate to strong thunderstorms will have the potential to produce 0.3-0.9" in 10-30 minutes. WORST CASE SCENARIO: Moisture levels remain higher than anticipated resulting in moderate to strong thunderstorms with the potential to produce heavy rainfall of 0.5-1.5" in 10-30 minutes and up to 2.5" in 45-60 minutes. A LOOK AHEAD: The rest of the week will be relatively quiet across northeastern Colorado, with highs in the upper 80's to low 90's with a slight chance of showers and thunderstorms on Friday. Models show a cool front will descend onto the plains overnight and early Sunday morning, lowering high temperatures into the mid 80's on Sunday afternoon over the plains with a slight chance of showers and thunderstorms possible. Wildfire smoke will continue to flow into the state, creating hazy skies through early next week. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM 0.1" (75%) to 0.3" (50%) to 0.9" (25%) MOD Arapahoe 200 PM TO 1000 PM 0.1" (75%) to 0.3" (50%) to 0.9" (25%) MOD Broomfield 200 PM TO 1000 PM 0.1" (75%) to 0.3" (50%) to 0.9" (20%) MOD Denver 200 PM TO 1000 PM 0.1" (75%) to 0.3" (50%) to 0.9" (25%) MOD Boulder 100 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.9" (20%) MOD Douglas 100 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.9" (25%) MOD Jefferson 100 PM TO 1000 PM 0.1" (80%) to 0.3" (50%) to 0.9" (20%) MOD Foothills above 6500ft       Boulder 1200 PM TO 1000 PM 0.1" (90%) to 0.3" (60%) to 0.9" (20%) MOD Douglas 1200 PM TO 1000 PM 0.1" (90%) to 0.3" (60%) to 0.9" (20%) MOD Jefferson 1200 PM TO 1000 PM 0.1" (90%) to 0.3" (60%) to 0.9" (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]