Flash Flood Prediction Program

Time: 908 AM Fri August 18, 2023 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- HOT TODAY WITH A GOOD CHANCE FOR AFTERNOON SHOWERS/THUNDERSTORMS A southwesterly flow aloft will dominate over the region today ahead of a weak disturbance that will move through this afternoon and evening. This weak disturbance will bring a good chance for widespread showers/thunderstorms starting around midday for the higher terrain foothills with multiple rounds of showers/thunderstorms possible into the evening hours, with chances likely tapering off between 9-10pm. Typical storm motions will be from the SW to NE, between 10-15mph, helping limit point rainfall amounts. However, stronger storms will have the potential to produce outflow boundaries with some slower moving storms along these boundaries. Due to dew points remaining in the low to mid 50s through the morning, there will be at least a MOD chance for Message 1s to be issued, mainly for the threat of a quick 0.5” in 10-15min from any outflow boundary induced storms. Overnight will be breezy and dry with lows dropping into the low to mid 60s on the plains with mid to upper 50s in the foothills. STORM RAINFALL POTENTIAL AND DURATION: Typical showers/weak thunderstorms will produce a 0.05-0.25” total, in 10-30 minutes. A moderate to strong shower/thunderstorm will produce 0.25-0.50” total in 10-30 minutes. WORST CASE SCENARIO: A strong, stationary thunderstorm, or training of thunderstorm cells will have the potential to produce 0.50-1.00” total in under 60 minutes. A LOOK AHEAD: Not much overall change to the upper-level pattern tomorrow bringing another chance for afternoon and evening showers/isolated thunderstorms. An overall decrease in moisture, both at the surface and aloft will result in a less chance for meaningful storms. Conditions start to dry out on Sunday as high temperatures remain in the 90s. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Arapahoe 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Boulder 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Broomfield 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Denver 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Douglas 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Jefferson 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Foothills above 6500ft       Boulder 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Douglas 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD Jefferson 100 PM TO 1000 PM 0.05" (75%) to 0.25" (50%) to 0.5" (25%) MOD MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]