Time: 844 AM Wed September 13, 2023 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- WARMER, SUNNY WITH A SLIGHT CHANCE FOR A FEW SHOWERS/ISOLATED THUNDERSTORMS Very little overall change to the weather pattern will keep mostly sunny and mild conditions to start the day. High temperatures will reach around 80 degrees this afternoon. Upper-level flow aloft will remain northwesterly, which will keep a slight chance for a few showers and possibly a thunderstorm or two, mainly along the foothills and Palmer Divide. A shower could potentially move into the District with the best chance for any showers being between 1-8pm. Due to warmer daytime temperatures and dew points currently in the mid to upper 40s, at least a LOW chance for Message 1s to be issued, mainly for a quick 0.5” in 10-15 minutes if stronger storms are able to develop. Skies will clear through the rest of the evening with mild and dry conditions expected through the overnight and into Thursday. Overnight lows will drop into the low 50s for the plains with mid to upper 40s along the foothills. STORM RAINFALL POTENTIAL AND DURATION: Typical showers will produce a trace to 0.25” total in 10-30 minutes. A moderate shower/thunderstorm will produce rainfall of 0.25" to 0.50” total in 10-30 minutes. WORST CASE SCENARIO: A strong shower/thunderstorm, or training of thunderstorms has the potential to produce 0.50” to 1.00” in under 60 minutes. A LOOK AHEAD: An increase in overall moisture Thursday brings a better chance for widespread showers/thunderstorms across the District with a chance for isolated moderate to heavy rainfall for portions of the District. Initial storm chances will be during the afternoon with showers picking up into the evening and possibly through the overnight and into Friday. Cooler Friday will likely help limit storm activity, with off and on showers possible throughout the day and into the evening. Once again a few of these showers will have the potential to produce some moderate to heavy rainfall which could potentially lead to some localized flooding. Especially if areas become saturated from the previous day’s storms. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 800 PM Trace (20%) to 0.25" (15%) to 0.5" (10%) LOW Arapahoe 200 PM TO 800 PM Trace (20%) to 0.25" (15%) to 0.5" (10%) LOW Boulder 200 PM TO 800 PM Trace (20%) to 0.25" (15%) to 0.5" (10%) LOW Broomfield 200 PM TO 800 PM Trace (20%) to 0.25" (15%) to 0.5" (10%) LOW Denver 200 PM TO 800 PM Trace (20%) to 0.25" (15%) to 0.5" (10%) LOW Douglas 200 PM TO 800 PM Trace (20%) to 0.25" (15%) to 0.5" (10%) LOW Jefferson 200 PM TO 800 PM Trace (20%) to 0.25" (15%) to 0.5" (10%) LOW Foothills above 6500ft       Boulder 100 PM TO 700 PM Trace (40%) to 0.25" (20%) to 0.5" (10%) LOW Douglas 100 PM TO 700 PM Trace (40%) to 0.25" (20%) to 0.5" (10%) LOW Jefferson 100 PM TO 700 PM Trace (40%) to 0.25" (20%) 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]