Time: 915 AM Tue September 28, 2021 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- ISOLATED AFTERNOON TO EVENING SHOWERS/THUNDERSTORMS AHEAD OF COLD FRONT TONIGHT - Today will be relatively warm with cloud cover increasing throughout the day. Temperatures will reach the upper 70s to low 80s across The District with dew points in upper 30s to around 40 degrees this afternoon and early evening. - There is a small chance for isolated showers and thunderstorms this afternoon to evening as moisture increases across the plains ahead of tonight's cold front. Best chance for rain shower and isolated thunderstorm activity will be between 1-9pm with off and on showers possible through the overnight and into Wednesday morning. Storm motions today will also be fairly brisk from the S/SW to N/NE between 10-20mph which will also help limit point rainfall amounts. - Showers and thunderstorms are expected to linger in the area through this evening and will primarily affect the west slopes. Can't rule out a stray shower or two along the foothills or Palmer Divide late tonight and into tomorrow morning. Overnight lows will drop into the upper 40's to low 50's for the plains with low to mid 40's along the foothills. STORM RAINFALL POTENTIAL AND DURATION: Typical rain showers will produce a trace to 0.1" of precipitation in 10-30 minutes. A moderate rain showers or isolated thunderstorm could produce 0.1-0.3" in 10-30 minutes. WORST CASE SCENARIO: A stronger thunderstorm, or training of thunderstorm cells has the potential to produce 0.3-0.8" in 60-90 minutes. A LOOK AHEAD: An upper-level disturbance is positioned over Colorado today and is on track to bring widespread showers across the foothills and adjacent plains through the end of this week. This pattern is also expected to bring a wave of fall temperatures to the high plains, and snow to higher elevations along the western slope. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 100 PM TO 900 PM Trace (30%) to 0.1" (15%) to 0.3" (5%) NONE Arapahoe 100 PM TO 900 PM Trace (30%) to 0.1" (15%) to 0.3" (5%) NONE Boulder 100 PM TO 900 PM Trace (30%) to 0.1" (15%) to 0.3" (5%) NONE Broomfield 100 PM TO 900 PM Trace (30%) to 0.1" (15%) to 0.3" (5%) NONE Denver 100 PM TO 900 PM Trace (30%) to 0.1" (15%) to 0.3" (5%) NONE Douglas 100 PM TO 900 PM Trace (30%) to 0.1" (15%) to 0.3" (5%) NONE Jefferson 100 PM TO 900 PM Trace (30%) to 0.1" (15%) to 0.3" (5%) NONE Foothills above 6500ft       Boulder 100 PM TO 900 PM Trace (40%) to 0.1" (20%) to 0.3" (10%) NONE Douglas 100 PM TO 900 PM Trace (40%) to 0.1" (20%) to 0.3" (10%) NONE Jefferson 100 PM TO 900 PM Trace (40%) to 0.1" (20%) to 0.3" (10%) 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]