Time: 943 AM Sat August 24, 2024 Forecaster: Tim Tonge ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- Scattered, gusty, late afternoon showers/thunderstorms, warm The monsoonal moisture transport setup remains in place today, though drier air at the surface will keep storm mode mostly gusty. Moist easterly surface flow from the northern plains and Coriolis forcing of this flow as it hits the mountains will cause increased pooling of surface moisture in the northwest District and foothills. By the time convective conditions are achieved by daytime heating, precipitable water (PWAT) values around 1.00" will be present in the Boulder Valley, with a decrease in moisture from northwest to southeast. Dry southwesterly winds from Park County will push some moisture out across the southern portion of the District, limiting PWAT values to around 0.80" in the eastern Douglas County portion of the District. Storm coverage where rainfall will be of concern today will be where the moisture is concentrated and higher elevations, though a stray storm moving into the main Denver metro is not out of the question. Most Denver storms will be in environments with 40-50 degree dewpoint depressions, especially in the southern metro, creating gusty outflow winds. In the higher elevations and northwestern District, conditions will be more favorable for small hail and heavy localized rainfall. Storms will clear around sunset, with clear skies and overnight lows around 60. STORM RAINFALL POTENTIAL AND DURATION: Typical showers and thunderstorms will produce 0.10"-0.25" of rainfall in 10-30 minutes. Stronger thunderstorms in favorable locations will produce 0.25"-0.75" in 10-30 minutes. WORST CASE SCENARIO: A strong/stationary thunderstorm, or training of thunderstorms along a boundary, may be capable of producing 1.50" in 60 minutes or less. A LOOK AHEAD: Late arriving showers and thunderstorms under similar setup tomorrow, though forcing will be amplified by approach of jet streak associated with Pacific Northwest trough. Trough will provide forcing for overnight showers into Monday morning, with chance for isolated thunderstorms Monday afternoon. Approach of the trough then cuts off monsoonal moisture transport Tuesday, with a small isolated chance Tuesday becoming likely dry Wednesday. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 800 PM 0.1" (50%) to 0.25" (30%) to 0.75" (10%) LOW Arapahoe 300 PM TO 800 PM 0.1" (50%) to 0.25" (30%) to 0.75" (10%) LOW Boulder 300 PM TO 800 PM 0.1" (70%) to 0.25" (40%) to 0.75" (10%) LOW Broomfield 300 PM TO 800 PM 0.1" (70%) to 0.25" (40%) to 0.75" (10%) LOW Denver 300 PM TO 800 PM 0.1" (50%) to 0.25" (30%) to 0.75" (10%) LOW Douglas 300 PM TO 800 PM 0.1" (70%) to 0.25" (40%) to 0.75" (10%) LOW Jefferson 300 PM TO 800 PM 0.1" (70%) to 0.25" (40%) to 0.75" (10%) LOW Foothills above 6500ft       Boulder 300 PM TO 800 PM 0.1" (70%) to 0.25" (40%) to 0.75" (10%) LOW Douglas 300 PM TO 800 PM 0.1" (70%) to 0.25" (40%) to 0.75" (10%) LOW Jefferson 300 PM TO 800 PM 0.1" (70%) to 0.25" (40%) to 0.75" (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]