Time: 1217 PM Tue August 1, 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 until midnight tonight. Cool temperatures with readings in the upper 70’s to lower 80’s currently is holding back the initiation of thunderstorms due to cloud cover this morning slowing daytime heating. Clouds have dissipated and good warming is underway, and thunderstorms are expected to develop over the next 1-3 hours and begin to impact the District later this afternoon and continue well into the evening with multiple rounds of showers and thunderstorms possible. 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 faster moving today as upper level winds have increased with typical storm motions of around 20mph from SW to NE. Slower moving large thunderstorms or training of thunderstorm cells are the likely culprits for extended periods of heavy rainfall. Due to all of the rain yesterday it may not take as much rain today to produce excessive runoff and flash flooding. Heavy rainfall will be the primary threat from thunderstorms today, but large hail and gusty winds are also possible from stronger storms. 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 training of thunderstorm cells may result in up to 3.5” of rain in 60-90 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Lakewood 2 Current TO 1159 PM 300 PM TO 1000 PM Wheat Ridge 2 Current TO 1159 PM 300 PM TO 1000 PM Arvada 2 Current TO 1159 PM 300 PM TO 1000 PM the City of Aurora 2 Current TO 1159 PM 300 PM TO 1000 PM Arapahoe County 2 Current TO 1159 PM 300 PM TO 1000 PM DIA 2 Current TO 1159 PM 300 PM TO 1000 PM Denver County 2 Current TO 1159 PM 300 PM TO 1000 PM Adams County 2 Current TO 1159 PM 300 PM TO 1000 PM Douglas County 2 Current TO 1159 PM 200 PM TO 1000 PM Broomfield County 2 Current TO 1159 PM 300 PM TO 1000 PM Jefferson County 2 Current TO 1159 PM 200 PM TO 1000 PM Boulder County 2 Current TO 1159 PM 200 PM TO 1000 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Arapahoe 300 PM TO 1159 PM 0.5" (80%) to 1" (50%) to 2" (30%) ISSUED Boulder 300 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Broomfield 300 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Denver 200 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Douglas 200 PM TO 1159 PM 0.5" (80%) to 1" (50%) to 2" (30%) ISSUED Jefferson 200 PM TO 1159 PM 0.5" (75%) to 1" (50%) to 2" (25%) ISSUED Foothills above 6500ft       Boulder 100 PM TO 1159 PM 0.5" (80%) to 1" (50%) to 2" (25%) ISSUED Douglas 100 PM TO 1159 PM 0.5" (80%) to 1" (50%) to 2" (25%) ISSUED Jefferson 100 PM TO 1159 PM 0.5" (80%) 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]