Time: 1019 AM Mon August 19, 2024 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- Scattered/numerous afternoon thunderstorms, few degrees cooler overall Morning cloud cover seems to be stabilizing the atmosphere slightly, but it won't change the fact that many ingredients for a message issuance day are present for the District. Upper-level monsoonal moisture and low-level plains moisture, advected into the District by surface winds out of the southeast, have combined to create precipitable water (PWAT) values of 1.05-1.20" across the District. Dewpoints along the plains are staggering for mid/late August (72 at time of writing in Fort Morgan, 66 in Limon), and with the development of the Denver Convergence Vorticity Zone (DCVZ), moisture and forcing will both be present across the District for thunderstorm development this afternoon. The current indication is that the worst of this activity will be east of the District, but pooling of moisture at the top of the Palmer Divide and in the Boulder Valley as a result of the DCVZ's circulation will lead to likely message issuance to cover bases in case the convergence zone sets up closer to the mountains than anticipated. Storms are expected to fire in the high country west of the District around noon, and move into the foothills and plains in the early afternoon. They will be scattered/numerous in nature, and carry the threat of heavy localized rainfall, medium to large size hail, and gusty outflow winds up to 60 mph before they clear out just after sunset. Skies will be calm overnight with temps in the low 60s. STORM RAINFALL POTENTIAL AND DURATION: Typical showers and thunderstorms will produce 0.30"-0.80" in 10-30 minutes. Stronger or slower moving thunderstorms will produce 0.80"-1.50" total in 30 minutes or less. WORST CASE SCENARIO: A stationary thunderstorm, or training of thunderstorms along a boundary, may be capable of producing 2.25" in 60 minutes or less. A LOOK AHEAD: Drier tomorrow, with storm coverage mostly over higher terrain of foothills and Palmer Divide. Then the seemingly relentless monsoon kicks back into place, with storm chances looking likely for the District from Wednesday on into the weekend. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Arapahoe 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Boulder 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Broomfield 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Denver 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Douglas 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Jefferson 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Foothills above 6500ft       Boulder 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Douglas 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) HIGH Jefferson 200 PM TO 800 PM 0.3" (60%) to 0.8" (40%) to 1.5" (20%) 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]