Flash Flood Prediction Program

Time: 849 AM Tue September 17, 2024 Forecaster: Aaron O ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- Strong Cold Front this Afternoon with Thunderstorms Likley Another day with highs in the mid to upper 80s as a cold front is expected to move through The District this afternoon. Dew points are expected to be in the mid 30s to the low 40s, and with Precipitable water values between 0.60” to 0.70”, will bring a LOW chance of Message level rainfall as scattered to widespread thunderstorms are expected this afternoon. Storms today will be quite fast as the SSW to NNE storm motion of 25-35 mph will significantly limit point rainfall amount. However, outflow boundaries from a stronger storm will have the potential for some erratic storm motions. These erratic storms will have the best potential for moderate to heavy rainfall with the biggest threat being a quick 0.5” in 10-20 minutes rather than any long-lasting rainfall. One round of storms is likely today with the best chance between 2-6pm. A few storms could become severe today, mainly for gusty wind 60+ mph and possibly hail up to 1.0”, favoring areas east of I-25. Chances for thunderstorms will end before sunset as the cold front moves out of The District and into the Eastern Plains, with skies clearing through the evening. Overnight conditions are expected to be mild and dry as temperatures drop to around 50 degrees on the plains with mid to upper 40s along the foothills. STORM RAINFALL POTENTIAL AND DURATION: Typical showers and thunderstorms will produce rainfall rates of up to 0.25” total in 15-30 minutes. Moderate to strong thunderstorms will produce between 0.25"-0.50" total in 10-30 minutes. WORST CASE SCENARIO: A strong stationary thunderstorm or training of thunderstorms have the potential to produce up to 1.00” total rainfall 30-60 minutes. A LOOK AHEAD: For the next several days, a high pressure system will build over the Intermountain West, keeping The District dry for the rest of the week. Next chance for precipitation will be this weekend with a passing weak cold front bringing our first real winter-like storm set up, with shallow and light precipitation for the afternoon and evening on Saturday. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 600 PM Trace (50%) to 0.3" (25%) to 0.5" (10%) LOW Arapahoe 200 PM TO 600 PM Trace (50%) to 0.3" (25%) to 0.5" (10%) LOW Boulder 200 PM TO 600 PM Trace (50%) to 0.3" (25%) to 0.5" (10%) LOW Broomfield 200 PM TO 600 PM Trace (50%) to 0.3" (25%) to 0.5" (10%) LOW Denver 200 PM TO 600 PM Trace (50%) to 0.3" (25%) to 0.5" (10%) LOW Douglas 200 PM TO 600 PM Trace (50%) to 0.3" (25%) to 0.5" (10%) LOW Jefferson 200 PM TO 600 PM Trace (50%) to 0.3" (25%) to 0.5" (10%) LOW Foothills above 6500ft       Boulder 200 PM TO 600 PM Trace (60%) to 0.3" (30%) to 0.5" (15%) LOW Douglas 200 PM TO 600 PM Trace (60%) to 0.3" (30%) to 0.5" (15%) LOW Jefferson 200 PM TO 600 PM Trace (60%) to 0.3" (30%) to 0.5" (15%) 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]