Time: 1206 PM Sun May 23, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S ISSUED FOR PORTIONS OF THE DISTRICT - Message 1's have been issued for the I-25 corridor eastward including Adams, Arapahoe, Denver and Douglas Counties until 4pm. - Dry air is approaching from the west but a line of thunderstorms is beginning to develop ahead of it over the plains and portions of the Palmer Divide. Surface moisture remains abundant over the plains currently and as temperatures continue to warm strong thunderstorms may develop in the deeper moisture along and E of I-25. Fast storm motions from S to N will limit point rainfall amounts from a single storm keeping the majority of the heavy rainfall brief but training of thunderstorm cells may result in a prolonged period of heavy rain that could lead to excessive runoff. - Strong thunderstorms may also become severe with large hail and gusty winds being the primary threats. As the dry air from the west moves into the District by mid afternoon thunderstorm chances will come to an end. Best chances for thunderstorm activity is until 4pm. STORM RAINFALL POTENTIAL AND DURATION: Typical rain showers/isolated thunderstorms will have the potential to produce a TR-0.3" in 10-30 minutes. A strong thunderstorm will have the potential to produce 0.3-0.8" in 10-30 minutes. WORST CASE SCENARIO: Training of thunderstorm cells may result in up to 1.5" of rain in 45-60 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME the City of Aurora 1 Current TO 400 PM Current TO 300 PM Arapahoe County 1 Current TO 400 PM Current TO 300 PM DIA 1 Current TO 400 PM Current TO 300 PM Denver County 1 Current TO 400 PM Current TO 300 PM Adams County 1 Current TO 400 PM Current TO 300 PM Douglas County 1 Current TO 400 PM Current TO 300 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 400 PM SUN Trace (95%) to 0.3" (60%) to 0.8" (15%) ISSUED Arapahoe Current TO 400 PM SUN Trace (95%) to 0.3" (60%) to 0.8" (15%) ISSUED Boulder Current TO 400 PM SUN Trace (80%) to 0.3" (40%) to 0.8" (10%) LOW Broomfield Current TO 400 PM SUN Trace (80%) to 0.3" (40%) to 0.8" (10%) LOW Denver Current TO 400 PM SUN Trace (95%) to 0.3" (60%) to 0.8" (15%) ISSUED Douglas Current TO 400 PM SUN Trace (95%) to 0.3" (60%) to 0.8" (15%) ISSUED Jefferson Current TO 400 PM SUN Trace (80%) to 0.3" (40%) to 0.8" (10%) LOW Foothills above 6500ft       Boulder Current TO 400 PM SUN Trace (75%) to 0.3" (30%) to 0.8" (5%) LOW Douglas Current TO 400 PM SUN Trace (75%) to 0.3" (30%) to 0.8" (5%) ISSUED Jefferson Current TO 400 PM SUN Trace (75%) to 0.3" (30%) to 0.8" (5%) 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]