Time: 908 AM Wed June 7, 2023 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- MID TO LATE AFTERNOON THUNDERSTORMS MAY PERSIST INTO THE EVENING WITH THE POTENTIAL FOR HEAVY RAINFALL The relentless pattern of slow moving afternoon and evening thunderstorms continues over the District today with stronger storms capable of producing heavy rainfall. Thunderstorms will first develop over the foothills and higher terrain of the Palmer Divide between noon and 2pm but these initial storms will have difficulty progressing eastward as upper level steering winds light are from S to N. This will likely delay the onset of thunderstorm chances over the plains as these first storms will stay over the higher terrain, but they will likely produce a rain cooled outflow boundary that pushes eastward from the foothills or northward from the Palmer Divide storms. These likely outflow boundaries will be the potential trigger for new storms on the plains initiating between 2-4pm. Widely scattered moderate to strong thunderstorms are then expected into the late afternoon with 1-2 rounds possible. Rain showers and possibly a weak thunderstorm will continue likely well into the evening with dry conditions expected to develop by around midnight. Surface dew points have decreased from yesterday, but ample moisture remains to fuel storms and stronger thunderstorm cells will be capable of producing heavy rainfall that may lead to excessive runoff. Some areas of the District are experiencing a saturated ground from rain over the previous days and runoff may occur quickly in these areas. STORM RAINFALL POTENTIAL AND DURATION: Weak thunderstorms will produce rainfall rates of 0.1-0.4” in 10-30 minutes. Moderate to strong thunderstorms will have the potential to produce rainfall rates of 0.4-1.0” in 10-30 minutes. WORST CASE SCENARIO: A slow moving or nearly stationary strong thunderstorm may result in up to 1.8” of rain in 45-60 minutes. A LOOK AHEAD: Daily chances for afternoon and evening thunderstorms will continue Thursday and Friday with widely scattered coverage. Stronger thunderstorms will continue to have the potential to produce heavy rainfall. Thunderstorm chances increase on Saturday as a cold front moves through and produces “upslope” flow into Sunday. Cooler Sunday with afternoon highs likely remaining in the 60’s. Rain showers are a sure bet on Sunday, but thunderstorm chances will hinge upon daytime heating and if temperatures remain too cool then precipitation may favor rain versus thunder. Should thunderstorms develop heavy rainfall will be possible. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 300 PM TO 1000 PM 0.1" (75%) to 0.4" (50%) to 1" (25%) HIGH Arapahoe 300 PM TO 1000 PM 0.1" (75%) to 0.4" (50%) to 1" (25%) HIGH Broomfield 300 PM TO 1000 PM 0.1" (75%) to 0.4" (50%) to 1" (25%) HIGH Denver 300 PM TO 1000 PM 0.1" (75%) to 0.4" (50%) to 1" (25%) HIGH Boulder 200 PM TO 1000 PM 0.1" (80%) to 0.4" (60%) to 1" (30%) HIGH Douglas 200 PM TO 1000 PM 0.1" (80%) to 0.4" (60%) to 1" (30%) HIGH Jefferson 200 PM TO 1000 PM 0.1" (80%) to 0.4" (60%) to 1" (30%) HIGH Foothills above 6500ft       Boulder 100 PM TO 1000 PM 0.1" (80%) to 0.4" (60%) to 1" (30%) HIGH Douglas 100 PM TO 1000 PM 0.1" (80%) to 0.4" (60%) to 1" (30%) HIGH Jefferson 100 PM TO 1000 PM 0.1" (80%) to 0.4" (60%) to 1" (30%) 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]