Time: 353 PM Mon July 31, 2023 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 2'S HAVE BEEN ISSUED FOR THE ENTIRE DISTRICT AND WILL BE VALID UNTIL MIDNIGHT Message 2’s (NWS Flood/Flash Flood Watch) have been issued for the entire District and will be valid from 4:00 PM until midnight tonight. Thunderstorms are expected to develop over the next 1-3 hours over the District and continue well into the evening with multiple rounds of showers and thunderstorms possible. Should thunderstorm activity persist past midnight Message 2’s may be extended into the early morning hours on Tuesday. Thunderstorms that develop later this afternoon and evening have ample moisture to work with and will be very capable of producing heavy rainfall that may lead to excessive runoff and flash flooding within the District. Storms will be relatively slow moving at 10-15mph allowing for extended periods of heavy rain. Prime time for thunderstorms will be from 5:00 PM until 11:30 PM. Heavy rainfall will be the primary threat from thunderstorms today, but large hail and gusty winds is also possible from stronger storms. The stronger thunderstorms may favor areas E of I-25 where surface moisture is more abundant. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce rainfall rates of 0.2-0.8” in 10-30 minutes. Strong thunderstorms will have the potential to produce rainfall rates of 0.8-2.0” of rain in 10-30 minutes. WORST CASE SCENARIO: A slow moving strong thunderstorm or a large thunderstorm complex may result in up to 3.5” of rain in 60-90 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Boulder County 2 400 PM TO 1159 PM 500 PM TO 1130 PM Jefferson County 2 400 PM TO 1159 PM 500 PM TO 1130 PM Broomfield County 2 400 PM TO 1159 PM 500 PM TO 1130 PM Douglas County 2 400 PM TO 1159 PM 500 PM TO 1130 PM Adams County 2 400 PM TO 1159 PM 500 PM TO 1130 PM Denver County 2 400 PM TO 1159 PM 500 PM TO 1130 PM DIA 2 400 PM TO 1159 PM 500 PM TO 1130 PM Arapahoe County 2 400 PM TO 1159 PM 500 PM TO 1130 PM the City of Aurora 2 400 PM TO 1159 PM 500 PM TO 1130 PM Arvada 2 400 PM TO 1159 PM 500 PM TO 1130 PM Wheat Ridge 2 400 PM TO 1159 PM 500 PM TO 1130 PM Lakewood 2 400 PM TO 1159 PM 500 PM TO 1130 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 430 PM TO 1159 PM 0.5" (80%) to 1" (50%) to 2" (30%) ISSUED Arapahoe 430 PM TO 1159 PM 0.5" (80%) to 1" (50%) to 2" (30%) ISSUED Boulder 430 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Broomfield 430 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Denver 430 PM TO 1159 PM 0.5" (80%) to 1" (50%) to 2" (30%) ISSUED Douglas 430 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Jefferson 430 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Foothills above 6500ft       Boulder Current TO 1159 PM MON 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Douglas Current TO 1159 PM MON 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Jefferson Current TO 1159 PM MON 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]