Time: 921 AM Sun July 30, 2023 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- SEASONABLE TEMPERATURES WITH SLOW MOVING ISOLATED AFTERNOON THUNDERSTORMS The District is located near the center of the ridge of high pressure aloft and will result in temperatures at or slightly above normal for the date and weak upper level steering winds will result in relatively slow storm motions. Afternoon highs will reach the 90-94 degree range over the plains with 80’s in the Front Range foothills. Normal high for Denver today is 90 degrees. Much like the past few days thunderstorms will initiate over the mountains and foothills W of the District by around noon or shortly after. Due to the weak upper level steering winds it will take some time for thunderstorms to develop over the plains but by 2 or 3pm storms will drift eastward or rain cooled outflow from the higher terrain storms may help generate new storms over the lower elevations. Thunderstorm coverage is expected to be isolated over the plains but the storms that do form will have the potential to produce moderate to brief heavy rainfall. Foothill storms will be more numerous and also contain a heavy rainfall threat. Prime time for thunderstorm activity will be from 2 or 3pm until around 9pm. After 9pm thunderstorm chances decrease, and generally dry conditions are expected for the later evening and overnight period. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce rainfall amounts of 0.1-0.5”. Strong thunderstorms will have the potential to produce rainfall rates of 0.5-1.2” of rain in 10-30 minutes. WORST CASE SCENARIO: A nearly stationary strong thunderstorm or a large/slow moving thunderstorm may result in up to 2.0” of rain in 45-60 minutes. A LOOK AHEAD: An uptick in thunderstorm activity is expected on Monday and thunderstorm coverage will increase further on Tuesday and Wednesday along with cooling temperatures. Ample moisture is available over the coming days for stronger storms to produce heavy rainfall that may lead to excessive runoff and possibly flash flooding in and around the District. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 900 PM 0.1" (60%) to 0.5" (30%) to 1" (15%) MOD Arapahoe 300 PM TO 900 PM 0.1" (60%) to 0.5" (30%) to 1" (15%) MOD Broomfield 300 PM TO 900 PM 0.1" (60%) to 0.5" (30%) to 1" (15%) MOD Denver 300 PM TO 900 PM 0.1" (60%) to 0.5" (30%) to 1" (15%) MOD Boulder 200 PM TO 900 PM 0.1" (60%) to 0.5" (30%) to 1" (15%) MOD Douglas 200 PM TO 900 PM 0.1" (60%) to 0.5" (30%) to 1" (15%) MOD Jefferson 200 PM TO 900 PM 0.1" (60%) to 0.5" (30%) to 1" (15%) MOD Foothills above 6500ft       Boulder 100 PM TO 900 PM 0.1" (80%) to 0.5" (40%) to 1" (20%) MOD Douglas 100 PM TO 900 PM 0.1" (80%) to 0.5" (40%) to 1" (20%) MOD Jefferson 100 PM TO 900 PM 0.1" (80%) to 0.5" (40%) to 1" (20%) 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]