Time: 840 AM Fri June 18, 2021 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- HEAT WAVE BREAKS! BETTER CHANCE FOR AFTERNOON RAIN/ISOLATED THUNDERSTORMS - Finally a reprieve from triple digit temperatures! A relatively weak cold front has just passed through Greeley from the N/NE which will continue to move southward and will effectively keep high temperatures in the upper 80's to low 90's this afternoon. This cold front will also help keep some surface moisture in place today with dew points in the 40's leading to a better chance for rain showers and isolated thunderstorms with a very slight chance for severe thunderstorms with brief heavy rain, gusty winds and hail around 1" in diameter. - Storms will initiate over the higher terrain after noon today with the best chance for storms across the District between 2-8pm with a few scattered rain/isolated thunderstorms after 8pm, favoring eastern portions of the District. Storm motions will be from the W/SW to E/NE between 10-15mph which will help limit point rainfall amounts, however a storm developing off an outflow boundary has the potential to produce moderate to brief heavy rainfall today. - Skies will gradually clear this evening with overnight lows dropping into the low to mid 60's for the plains with upper 50's to around 60 along the foothills. STORM RAINFALL POTENTIAL AND DURATION: Typical rain showers/isolated thunderstorms will produce a trace-0.2" of rainfall in 10-30 minutes. A moderate rain shower/isolated thunderstorms will produce 0.2-0.5" in 10-30 minutes. WORST CASE SCENARIO: An anchored thunderstorm, or a a stronger thunderstorm developed off an outflow boundary has the potential to produce 1" of rainfall in 45-60 minutes. A LOOK AHEAD: Storm chances pick up into the weekend as high temperatures remain in the mid 80's to low 90's both Saturday and Sunday. Similar conditions will be in place for Saturday with afternoon and early evening rain/isolated thunderstorms. The best chance for heavy rainfall will be Sunday as an uptick in upper-level moisture moves over the region with rain chances continuing through the overnight and into Monday morning. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (15%) LOW Arapahoe 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (15%) LOW Boulder 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (15%) LOW Broomfield 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (15%) LOW Denver 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (15%) LOW Douglas 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (15%) LOW Jefferson 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (15%) LOW Foothills above 6500ft       Boulder 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (10%) LOW Douglas 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (10%) LOW Jefferson 200 PM TO 800 PM Trace (50%) to 0.2" (30%) to 0.5" (10%) 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]