Flash Flood Prediction Program

Time: 825 AM Fri July 23, 2021 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- HOT AGAIN TODAY WITH ANOTHER CHANCE FOR AFTERNOON AND EVENING RAIN SHOWERS/ISOLATED THUNDERSTORMS - Not much chance in the overall pattern today as high temperatures are expected to reach the low to mid 90's once again on the plains with mid to upper 80's along the foothills. Elevated monsoonal moisture remains in place over the region resulting in another chance for isolated heavy rainfall this afternoon and evening with rain showers possible through the overnight and into Saturday morning. - Thunderstorms will develop over the mountains/foothills during the afternoon. Thunderstorm chances increase over the plains between 3-4pm with prime time for thunderstorms from 4-10pm. Additional showers and possibly a weak isolated thunderstorms will remain possible through the overnight. At least 1 strong round of thunderstorms is expected this afternoon, with a good chance for an additional rounds of rain showers/isolated thunderstorms in the evening, however, the initial afternoon round likely being the strongest and will have the best chance for heavy rainfall. Any heavy rainfall threat should diminish after 10pm this evening. - Relatively slow overall storm motions from W to E between 3-8mph will allow for extended periods of heavy rain under stronger storms. Storm motions may also become erratic or stationary at times due to outflow boundaries/gust front interactions. This behavior will also increase the chance for isolated heavy rainfall this afternoon and into this evening. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce TR-0.3" in 10-30 minutes. Strong thunderstorms have the potential to produce 0.3-1.0" of heavy rain in 10-30 minutes. WORST CASE SCENARIO: A nearly stationary strong thunderstorm may result in up to 2.0" in 60 minutes or less. A LOOK AHEAD: A cold front will move through the region overnight and into Saturday effectively dropping Saturday's high temperatures back into the mid to upper 80's for the plains with upper 70's to around 80 for the foothills. This front will allow a chance for rain showers and isolated thunderstorms throughout the day Saturday, however, the intensity of rainfall will hinge on whether temperatures increase sufficiently during the day to produce stronger storms. the most likely outcome at this time will be weak to moderate rain showers/isolated thunderstorms. Conditions start to dry out slightly Sunday with a slight chance for afternoon rain showers/isolated thunderstorms with minimal threat for heavy rainfall for now. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 1000 PM Trace (75%) to 0.3" (50%) to 1.0" (15%) MOD Arapahoe 300 PM TO 1000 PM Trace (75%) to 0.3" (50%) to 1.0" (15%) MOD Boulder 300 PM TO 1000 PM Trace (75%) to 0.3" (50%) to 1.0" (15%) MOD Broomfield 300 PM TO 1000 PM Trace (75%) to 0.3" (50%) to 1.0" (15%) MOD Denver 300 PM TO 1000 PM Trace (75%) to 0.3" (50%) to 1.0" (15%) MOD Douglas 300 PM TO 1000 PM Trace (75%) to 0.3" (50%) to 1.0" (15%) MOD Jefferson 300 PM TO 1000 PM Trace (75%) to 0.3" (50%) to 1.0" (15%) MOD Foothills above 6500ft       Boulder 300 PM TO 1000 PM Trace (80%) to 0.3" (60%) to 1.0" (30%) HIGH Douglas 300 PM TO 1000 PM Trace (80%) to 0.3" (60%) to 1.0" (30%) HIGH Jefferson 300 PM TO 1000 PM Trace (80%) to 0.3" (60%) to 1.0" (30%) 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]