Time: 741 AM Thu July 20, 2023 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- COOLER AND CLOUDY WITH OFF AND ON SHOWERS/THUNDERSTORMS THROUGHOUT THE DAY AND INTO THE EVENING Cooler and cloudy to start the day as a disturbance is poised to move over the District throughout the day today, through the evening with a slight chance for some overnight showers/isolated thunderstorms. Currently temperatures are in the low 60’s with highs expected in the upper 70’s to around 80 this afternoon. Dew points are currently elevated, in the mid to upper 50’s and will likely remain as the day progresses resulting in a good chance for isolated heavy rainfall today. Showers and thunderstorms have already initiated over portions of the District and will likely continue through the afternoon and evening. The best chance for storm activity within the District will be from NOW through midnight, with a few lingering showers through the overnight, tapering off between 2-4am. Multiple rounds of showers/thunderstorms will be possible this morning, afternoon and evening with a good chance of isolated heavy rainfall resulting in a HIGH chance for Message 1’s to be issued. Storm motions will be the typical W to E motions between 15-25mph which should help limit point rainfall amounts with some erratic storm movement possible off outflow boundaries. Storms may also contain large hail, strong winds, frequent cloud-to-ground lightning and possible an isolated land spout/weak tornado, mainly for eastern portions of the District, especially if temperatures increase into the 80’s. STORM RAINFALL POTENTIAL AND DURATION: Typical rain showers and thunderstorms will produce a 0.10-0.50” total, in 10-30 minutes. A moderate to strong thunderstorm will produce 0.50-1.00” total, in 10-30 minutes. WORST CASE SCENARIO: A strong thunderstorm anchors off an outflow boundary, or training of thunderstorms could potentially produce up to 2.0” total in 45-60 minutes. A LOOK AHEAD: Similar conditions remain in place Friday, although upper-level shifts northwesterly, leading to slightly less chances for heavy rainfall as storms expected to increase in speed during the day and into the evening Friday. Currently at least a LOW threat for Heavy rainfall will be possible tomorrow. Saturday should dry out with minimal storm chances. A slightly better chance for storms Sunday afternoon and early evening, with storm chances tapering off by midnight. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Arapahoe Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Boulder Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Broomfield Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Denver Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Douglas Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Jefferson Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Foothills above 6500ft       Boulder Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Douglas Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH Jefferson Current TO 1000 PM THU 0.1" (90%) to 0.5" (50%) to 1" (25%) HIGH MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]