Flash Flood Prediction Program

Time: 838 AM Thu July 22, 2021 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- HOT AND A LITTLE HAZY TODAY WITH A CHANCE FOR ISOLATED AFTERNOON RAIN SHOWERS/THUNDERSTORMS - Another hot and hazy day for Colorado as highs reach the low to mid 90's on the plains this afternoon with mid to upper 80's along the foothills. Colorado will continue to tap into monsoon moisture today resulting in another chance for isolated heavy rainfall this afternoon and evening. - Thunderstorms will develop over the mountains/foothills during the afternoon. Thunderstorm chances increase over the plains between 3-4pm with prime time from 4-10pm. Additional showers and weaker thunderstorms will remain possible through midnight. At least 1 round of thunderstorms is expected this afternoon, with a good chance for an additional round 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. - Relatively slow storm motions from W to E between 5-10mph will allow for extended periods of heavy rain under stronger storms. Storm motions may also become erratic or potential stationary at times due to outflow boundaries/gust front interactions. This behavior will also increase the chance for isolated heavy rainfall this afternoon. 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: As the high-pressure ridge remains over the Central/Southwest US, Colorado will continue to tap into monsoon moisture through the weekend with afternoon/evening rain showers/isolated thunderstorm chances both Saturday and Sunday. The intensity of rainfall will hinge heavily on how much surface moisture can remain in place throughout the day with upper 40's to low 50's dew points projected Saturday, at least a low chance will remain for isolated heavy rainfall. Conditions dry out at the surface slightly on Sunday, however a very low threat will remain for isolated heavy rainfall at this time. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM Trace (50%) to 0.3" (20%) to 1.0" (10%) LOW Arapahoe 200 PM TO 1000 PM Trace (50%) to 0.3" (20%) to 1.0" (10%) LOW Boulder 200 PM TO 1000 PM Trace (50%) to 0.3" (20%) to 1.0" (10%) LOW Broomfield 200 PM TO 1000 PM Trace (50%) to 0.3" (20%) to 1.0" (10%) LOW Denver 200 PM TO 1000 PM Trace (50%) to 0.3" (20%) to 1.0" (10%) LOW Douglas 200 PM TO 1000 PM Trace (50%) to 0.3" (20%) to 1.0" (10%) LOW Jefferson 200 PM TO 1000 PM Trace (50%) to 0.3" (20%) to 1.0" (10%) LOW Foothills above 6500ft       Boulder 200 PM TO 1000 PM Trace (60%) to 0.3" (30%) to 1.0" (15%) MOD Douglas 200 PM TO 1000 PM Trace (60%) to 0.3" (30%) to 1.0" (15%) MOD Jefferson 200 PM TO 1000 PM Trace (60%) to 0.3" (30%) to 1.0" (15%) MOD MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]