Flash Flood Prediction Program

Time: 854 AM Thu September 2, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- WIDELY SCATTERED AFTERNOON/EVENING SHOWERS/THUNDERSTORMS FAVORING THE HIGHER TERRAIN - Behind the trough of low pressure that moved through overnight temperatures will be cooler today with highs in the 70's to lower 80's over the plains. With more moisture to work with at the surface today isolated to widely scattered showers and thunderstorms will develop as early as noon over the foothills. - Rain showers and weak to moderate thunderstorms are expected to favor the higher terrain of the foothills and areas S of I-70 this afternoon over the Palmer Divide. Best chances for shower and thunderstorm activity will be between 1-9pm with lingering showers and possibly a weak thunderstorm possible until around midnight. - Showers and thunderstorms will be relatively fast moving from W to E at around 20mph helping to reduce point rainfall amounts from a single storm. Typical storms are expected to be weak to moderate in intensity but a stronger storm cannot be completely ruled out. If a stronger storm were to develop it would be capable of producing brief heavy rainfall, likely favoring the foothills and Palmer Divide region outside the District. STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce a trace to 0.1" of rain. Weak to moderate thunderstorms will produce 0.1-0.4" in 10-30 minutes. WORST CASE SCENARIO: A strong, slower moving thunderstorm is able to develop with the potential to produce heavy rainfall of up to 0.4-1.2" in 10-30 minutes. A LOOK AHEAD: Temperatures will continue to trend in the 70's and 80's for highs on Friday. Friday afternoon an upper level disturbance will move through and likely produce a round or two or moderate to strong thunderstorms sometime between noon-6pm. The thunderstorms are expected to be relatively fast moving but will be capable of producing brief heavy rainfall and possibly severe weather with hail and gusty winds being the primary threats. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 100 PM TO 900 PM Trace (75%) to 0.2" (40%) to 0.4" (10%) NONE Arapahoe 100 PM TO 900 PM Trace (75%) to 0.2" (40%) to 0.4" (10%) NONE Boulder 100 PM TO 900 PM Trace (80%) to 0.2" (45%) to 0.4" (15%) LOW Broomfield 100 PM TO 900 PM Trace (75%) to 0.2" (40%) to 0.4" (10%) NONE Denver 100 PM TO 900 PM Trace (75%) to 0.2" (40%) to 0.4" (10%) NONE Douglas 100 PM TO 900 PM Trace (90%) to 0.2" (50%) to 0.4" (20%) LOW Jefferson 100 PM TO 900 PM Trace (90%) to 0.2" (50%) to 0.4" (20%) LOW Foothills above 6500ft       Boulder 1200 PM TO 900 PM Trace (95%) to 0.2" (50%) to 0.4" (25%) LOW Douglas 1200 PM TO 900 PM Trace (95%) to 0.2" (50%) to 0.4" (25%) LOW Jefferson 1200 PM TO 900 PM Trace (95%) to 0.2" (50%) to 0.4" (25%) 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]