Time: 929 AM Wed September 1, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- INCREASING CLOUD COVER WITH LATE AFTERNOON AND EVENING SHOWERS/THUNDERSTORMS POSSIBLE - A trough of low pressure is on the approach and will result in an increase in mid and upper level moisture leading to more cloud cover over the District today. The lower levels of the atmosphere remain relatively dry and will take some time to moisten resulting in a late onset to the chances for showers and thunderstorms. - Most of the moisture associated with the trough of low pressure will remain along and west of the Continental Divide today. Chances for showers and weak thunderstorms increase over the higher terrain between 2-4pm and over the plains between 4-6pm. Best chances for showers and perhaps a weak to moderate thunderstorm will be from 6-10pm with lingering activity possible until midnight. Beyond midnight a few lingering rain showers may persist, favoring W/NW areas of the District. - Upper level steering winds from SW to NE at 15-20mph will keep the showers and any thunderstorms that manage to develop moving along, reducing the threat for heavy rainfall despite moisture on the increase as the day wears on. Although not expected if a strong thunderstorm is able to develop this evening brief heavy rainfall would be possible. If the threat for strong thunderstorms increases the HPO will be updated. STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce a trace to 0.1" of rain. Weak to moderate thunderstorms will have the potential to produce 0.1-0.3" in 10-30 minutes. WORST CASE SCENARIO: A strong thunderstorm is able to develop this evening with the potential to produce 0.3-0.9" in 10-30 minutes. A LOOK AHEAD: Much cooler Thursday with highs only in the upper 70's to lower 80's over the plains. With more moisture to work with if temperatures warm sufficiently thunderstorms will have the potential to produce brief heavy rain. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 600 PM TO 1200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Arapahoe 600 PM TO 1200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Broomfield 600 PM TO 1200 AM THU Trace (70%) to 0.1" (35%) to 0.3" (15%) NONE Denver 600 PM TO 1200 AM THU Trace (70%) to 0.1" (35%) to 0.3" (15%) NONE Boulder 500 PM TO 200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Douglas 500 PM TO 200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Jefferson 500 PM TO 200 AM THU Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Foothills above 6500ft       Boulder 400 PM TO 400 AM THU Trace (85%) to 0.1" (50%) to 0.3" (20%) NONE Douglas 400 PM TO 400 AM THU Trace (85%) to 0.1" (50%) to 0.3" (20%) NONE Jefferson 400 PM TO 400 AM THU Trace (85%) to 0.1" (50%) to 0.3" (20%) 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]