Flash Flood Prediction Program

Time: 848 AM Tue May 18, 2021 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- ANOTHER CLOUDY AND COOL DAY WITH DAYTIME RAIN SHOWERS/ISOLATED THUNDERSTORMS - Lingering cloud cover and patchy fog this morning as a disturbance continues to move slowly across SE Colorado. Temperatures today will remain cooler with highs reaching the upper 50s to low 60s on the plains this afternoon with low to mid 50's along the foothills. - A push of moisture from the east will move into the region this morning which will bring a chance for rain showers with isolated thunderstorms. Best chance for storm activity will from 10am until 6pm with a slight chance for lingering rain showers after 6pm with dry conditions expected after 8pm. Skies will gradually clear through the overnight and into Wednesday morning. - Although cooler today, there are enough ingredients with modest moisture in place, 45-50 dewpoints, and slow storm motions, if a strong thunderstorm develops, it could have the potential for heavy rainfall that would lead to excessive runoff. Storm motions will generally be from E to W at 5-10mph but stronger storms may anchor or move erratically along gust fronts/outflow boundaries. Stronger storms may also contain frequent lightning and hail. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will have the potential to produce 0.05-0.3" in 10-30 minutes. Strong thunderstorms will have the potential to produce 0.3-0.6" in 10-30 minutes. WORST CASE SCENARIO: An anchored strong thunderstorm or training of thunderstorm cells may result in up to 1.2" of rain in 60 minutes or less. A LOOK AHEAD: Wednesday will be warmer and sunny as high temperatures jump back into the low 70's on the plains with low 60's along the foothills. Another chance for afternoon rain/isolated thunderstorms with decreased surface moisture the threat for any heavy rainfall will be minimal. A small ridge of high-pressure arrives Thursday bring high temperatures into the low 80's along with dry conditions. Friday remains warm with highs around 80 with high pressure quickly breaking down leading to another active weekend with rain/thunderstorm chances through Sunday. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 1000 AM TO 700 PM 0.1" (50%) to 0.3" (30%) to 0.6" (10%) LOW Arapahoe 1000 AM TO 700 PM 0.1" (60%) to 0.3" (40%) to 0.6" (15%) LOW Boulder 1000 AM TO 700 PM 0.1" (50%) to 0.3" (30%) to 0.6" (10%) LOW Broomfield 1000 AM TO 700 PM 0.1" (50%) to 0.3" (30%) to 0.6" (10%) LOW Denver 1000 AM TO 700 PM 0.1" (60%) to 0.3" (40%) to 0.6" (15%) LOW Douglas 1000 AM TO 700 PM 0.1" (70%) to 0.3" (50%) to 0.6" (25%) LOW Jefferson 1000 AM TO 700 PM 0.1" (70%) to 0.3" (50%) to 0.6" (25%) LOW Foothills above 6500ft       Boulder 1100 AM TO 700 PM 0.1" (50%) to 0.3" (30%) to 0.6" (10%) LOW Douglas 1100 AM TO 700 PM 0.1" (60%) to 0.3" (40%) to 0.6" (20%) LOW Jefferson 1100 AM TO 700 PM 0.1" (60%) to 0.3" (40%) to 0.6" (20%) 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]