Flash Flood Prediction Program

Time: 1210 PM Sun July 24, 2022 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S ISSUED FOR THE ENTIRE DISTRICT/BOULDER AND DOUGLAS COUNTIES TRANSITION TO MESSAGE 2'S AT 3:00PM - Message 1's have been issued for the entire District and will be valid until 10:00 PM for all Counties except Boulder and Douglas as they transition to Message 2's. The NWS in Boulder has issued a Flash Flood Watch for the higher terrain of Boulder County above 6,000ft from 3:00 PM until Midnight. The NWS has also issued a Flood Watch for the E 2/3's of Douglas County above 6,000ft from 3:00 PM until Midnight and implies flash flooding, thus Message 2's will supersede the Message 1's for Boulder and Douglas Counties and will go into effect at 3:00 PM. The Message 2's from the MHFD will be valid until 10:00 PM to match the Message 1's end time as the Watches are expected to be cancelled early as the stronger storms are likely well east of the I-25 corridor by that time. Message 1's and 2's may be extended until midnight if a flooding threat remains. Although NWS Flood/Flash Flood Watches are not in effect for the remainder of the District the flood threat is elevated area wide. - Thunderstorms will begin to initiate over the next 1-2 hours over the higher terrain to the W and S of the District. Upper level steering winds from W to E or WSW to ENE at 15-20mph will push the storms onto the plains into the early afternoon. Prime time for moderate to strong thunderstorms will be from 2:00 PM to 9:00 PM. 1-3 rounds of storms are expected through the afternoon into the early evening. Large thunderstorms or briefly anchored thunderstorms will pose the greatest threat for extended periods of heavy rainfall. The first or second round of storms will likely be the strongest of the day. - Moderate to strong thunderstorms that develop today will be efficient rainfall producers as moisture levels are very high for Colorado standards. Even moderate thunderstorms will have the potential to produce heavy rainfall and strong thunderstorms will be very capable of producing heavy downpours that may lead to excessive runoff and possibly flash flooding. STORM RAINFALL POTENTIAL AND DURATION: Weak thunderstorms will produce 0.3-0.8" in 10-30 minutes. Moderate to strong thunderstorms will have the potential to produce rainfall rates of 0.8-2.0 in 10-30 minutes. WORST CASE SCENARIO: A large thunderstorm complex or a slower moving large thunderstorm may result in rainfall rates of 1.0-2.5" in 10-30 minutes and up to 3.5" of heavy rain in 45-75 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Boulder County 1 100 PM TO 300 PM 100 PM TO 900 PM Jefferson County 1 100 PM TO 1000 PM 100 PM TO 900 PM Broomfield County 1 100 PM TO 1000 PM 200 PM TO 900 PM Douglas County 1 100 PM TO 300 PM 100 PM TO 900 PM Adams County 1 100 PM TO 1000 PM 200 PM TO 900 PM Denver County 1 100 PM TO 1000 PM 200 PM TO 900 PM DIA 1 100 PM TO 1000 PM 200 PM TO 900 PM Arapahoe County 1 100 PM TO 1000 PM 200 PM TO 900 PM the City of Aurora 1 100 PM TO 1000 PM 200 PM TO 900 PM Arvada 1 100 PM TO 1000 PM 200 PM TO 900 PM Wheat Ridge 1 100 PM TO 1000 PM 200 PM TO 900 PM Lakewood 1 100 PM TO 1000 PM 200 PM TO 900 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Arapahoe 100 PM TO 1000 PM 0.2" (95%) to 0.8" (75%) to 2.0" (30%) HIGH Boulder 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Broomfield 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (25%) HIGH Denver 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Douglas 100 PM TO 1000 PM 0.2" (95%) to 0.8" (75%) to 2.0" (30%) HIGH Jefferson 100 PM TO 1000 PM 0.2" (95%) to 0.8" (70%) to 2.0" (20%) HIGH Foothills above 6500ft       Boulder Current TO 1000 PM SUN 0.2" (100%) to 0.8" (75%) to 2.0" (25%) HIGH Douglas Current TO 1000 PM SUN 0.2" (100%) to 0.8" (75%) to 2.0" (30%) HIGH Jefferson Current TO 1000 PM SUN 0.2" (100%) to 0.8" (75%) to 2.0" (25%) HIGH MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]