Flash Flood Prediction Program

Time: 739 PM Tue April 27, 2021 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 1'S WILL BE ALLOWED TO EXPIRE AT 8PM, RAIN SHOWERS TO CONTINUE OVERNIGHT WITH ACCUMULATING SNOW IN THE FOOTHILLS - Message 1's issued for Adams, Arapahoe/Aurora, Denver/DIA, and Douglas Counties will be allowed to expire at 8pm this evening as the heavy rainfall threat has ended but the rain is far from over... - Thunderstorm activity is currently transitioning to a widespread rain over the District. A "wetting" rain will continue into the evening with some lulls at times. The snow snow line will be gradually lowering to between 5,000-6,000ft by tomorrow morning with accumulating snow in the foothills and over the Palmer Divide. Rain will generally fall at rates of 0.10-0.50"/hr through 10pm then be in the 0.05-0.25"/hr rate into the morning (rain or melted snow equivalent). - Rain, mix, snow pending elevation tomorrow at daybreak will gradually decrease through the morning with snow changing back to rain over the lower elevations of the District as the snow line rises as temperatures slowly warm. Best chances for additional moisture Wednesday will be through 10am with lingering showers possible into the afternoon before drying out completely. Additional rainfall amounts this evening and overnight expected to range from 0.6-1.2" most areas with isolated higher and lower amounts. STORM RAINFALL POTENTIAL AND DURATION: Steady rain will have the potential to produce 0.1-0.5" of rain in 60 minutes through 10pm. After 10pm rainfall rates (rain or melted snow equivalent) are expected to lessen into the 0.1-0.3" in 60 minute range. WORST CASE SCENARIO: Moderate to heavy non-thunderstorm rain may result in up to 1.0" of rain in 60-90 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Douglas County 1 Current TO 800 PM Current TO 800 PM Adams County 1 Current TO 800 PM Current TO 800 PM Denver County 1 Current TO 800 PM Current TO 800 PM DIA 1 Current TO 800 PM Current TO 800 PM Arapahoe County 1 Current TO 800 PM Current TO 800 PM the City of Aurora 1 Current TO 800 PM Current TO 800 PM County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 60-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (30%) NONE Arapahoe Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (30%) NONE Boulder Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (30%) NONE Broomfield Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (30%) NONE Denver Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (30%) NONE Douglas Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (30%) NONE Jefferson Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (30%) NONE Foothills above 6500ft       Boulder Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (15%) NONE Douglas Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (15%) NONE Jefferson Current TO 1000 AM WED 0.1" (100%) to 0.2" (80%) to 0.5" (15%) NONE MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]