Time: 811 PM Thu August 26, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- ROUND OF SHOWERS/THUNDERSTORMS TO CLIP NORTHERN AREAS OF THE DISTRICT LATE THIS EVENING - Tail end of an upper level disturbance is expected to graze northern areas of the District this evening. As this disturbance passes between 10pm and 2am there will be a modest chance for showers and thunderstorms, favoring areas N of I-70 with lesser chances southward. Being the furthest north, Boulder County will have the best chances for measurable rain overnight. - Showers and thunderstorms will be fast moving from SW to NE at 20-30mph which is expected to keep the flooding threat at bay but a stronger storm may still be capable of producing brief heavy rainfall as surface moisture slowly returns. Fast moving rain showers and weak to briefly moderate thunderstorms are expected to be the main culprits tonight. - After 2am any shower and thunderstorm activity is expected to have pushed east of the District with dry conditions for the remainder of the overnight period. STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce a trace to 0.1" of rain. Weak to moderate thunderstorms will have the potential to produce 0.1-0.4" in 10-30 minutes. WORST CASE SCENARIO: A strong thunderstorm develops with the potential to produce 0.3-0.9" of heavy rainfall in 10-30 minutes. A LOOK AHEAD: Conditions are trending dry for Friday under sunny to mostly sunny skies with temperatures running above seasonal averages. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 1000 PM TO 200 AM FRI Trace (60%) to 0.2" (30%) to 0.4" (15%) LOW Arapahoe 1000 PM TO 200 AM FRI Trace (50%) to 0.2" (20%) to 0.4" (10%) NONE Boulder 1000 PM TO 200 AM FRI Trace (90%) to 0.2" (60%) to 0.4" (20%) LOW Broomfield 1000 PM TO 200 AM FRI Trace (80%) to 0.2" (40%) to 0.4" (20%) LOW Denver 1000 PM TO 200 AM FRI Trace (60%) to 0.2" (30%) to 0.4" (10%) NONE Douglas 1000 PM TO 200 AM FRI Trace (40%) to 0.2" (20%) to 0.4" (10%) NONE Jefferson 1000 PM TO 200 AM FRI Trace (80%) to 0.2" (40%) to 0.4" (20%) LOW Foothills above 6500ft       Douglas 1000 PM TO 200 AM FRI Trace (50%) to 0.2" (25%) to 0.4" (10%) NONE Jefferson 1000 PM TO 200 AM FRI Trace (90%) to 0.2" (60%) to 0.4" (30%) LOW Boulder 900 PM TO 100 AM FRI Trace (100%) to 0.2" (70%) to 0.4" (40%) LOW MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]