Flash Flood Prediction Program

Time: 907 AM Mon September 13, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- COOLER/BREEZY WITH ISOLATED AFTERNOON AND EVENING THUNDERSTORMS - A cold front is currently moving through the District from N to S at this time and should shave a couple degrees off of high temperatures today with readings in the upper 70's and lower 80's over the plains. An isolated rain shower may develop later this morning over the higher terrain with the plains remaining generally dry until this afternoon. - Chances for isolated showers and thunderstorms will increase over the plains between 1-3pm. Chances for shower and thunderstorm activity will then persist well into the evening but the storm coverage will be spotty and not everyone will experience a shower or thunderstorm today. Best chances look to be N areas of the District and in particular over Boulder County. Surface moisture is only modest behind the front leading to thunderstorms that develop generally being weak to briefly moderate in intensity. - Upper level steering winds from W to E at 15-25mph will keep the showers and thunderstorms moving along keeping precipitation durations brief and overall rainfall amounts on the light side. After 10pm the best chances for shower activity will be pushing S and E but a stray rain shower cannot be ruled out during the overnight period. STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce a trace to 0.1" of rain. Weak to briefly moderate thunderstorms will have the potential to produce 0.1-0.3" of rain in 10-30 minutes. WORST CASE SCENARIO: A slower moving briefly strong thunderstorm will have the potential to produce rainfall rates of 0.2-0.6" in 10-30 minutes. A LOOK AHEAD: Cooler Tuesday as another disturbance moves through with highs in the 70's over the plains with a good chance for widely scattered showers and isolated thunderstorms during the day. Best chances for more persistent showers/thunderstorms appear to be over the southern half of the District and in particular over Douglas County. Depending upon available surface moisture some storms Tuesday may contain moderate to brief heavy rainfall. A stretch of dry weather is then expected Wednesday through Friday with plenty of sunshine and temperatures running above normal for this time of year. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM Trace (70%) to 0.1" (30%) to 0.3" (15%) NONE Arapahoe 200 PM TO 1000 PM Trace (60%) to 0.1" (30%) to 0.3" (15%) NONE Broomfield 200 PM TO 1000 PM Trace (75%) to 0.1" (35%) to 0.3" (15%) NONE Denver 200 PM TO 1000 PM Trace (60%) to 0.1" (30%) to 0.3" (15%) NONE Boulder 100 PM TO 1000 PM Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE Douglas 100 PM TO 1000 PM Trace (60%) to 0.1" (30%) to 0.3" (15%) NONE Jefferson 100 PM TO 1000 PM Trace (75%) to 0.1" (35%) to 0.3" (15%) NONE Foothills above 6500ft       Boulder 1200 PM TO 1000 PM Trace (90%) to 0.1" (50%) to 0.3" (25%) NONE Douglas 1200 PM TO 1000 PM Trace (60%) to 0.1" (30%) to 0.3" (15%) NONE Jefferson 1200 PM TO 1000 PM Trace (80%) to 0.1" (40%) to 0.3" (20%) NONE MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]