Time: 918 AM Wed May 17, 2023 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- ABOVE NORMAL TEMPERATURES WITH ISOLATED AFTERNOON THUNDERSTORMS/FLASH FLOOD THREAT INCREASES TOMORROW Temperatures will continue to run above seasonal averages today with afternoon highs reaching the upper 70’s to around 80 over the plains with 60’s in the Front Range foothills. Normal high for Denver today is 72 degrees. Sunny skies this morning will give way to a build-up of convective clouds over the higher terrain by around noon and isolated to widely scattered thunderstorms will move over the plains during the afternoon and evening. The showers and thunderstorms that develop today will move from NW to SE at 15-20mph and are expected to be brief in duration and generally weak producing light to briefly moderate rain. Should a strong thunderstorm develop brief heavy rainfall may occur, but the chances look low with dew points dropping into the upper 30’s to lower 40’s this afternoon limiting the fuel for storms. Best chances for thunderstorms will be between 2:00-9:00pm. A cold front will be moving through overnight and may generate a light rain shower or two after midnight into Thursday morning. Rainfall amounts overnight will be minimal, generally 0.1” or less but the cold front will usher in low level moisture and set the stage for a more active weather day on Thursday with the potential for heavy rainfall. STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce a trace to 0.1” of rain in 10-30 minutes. Weak to moderate thunderstorms will produce rainfall rates of 0.1-0.4” in 10-30 minutes. WORST CASE SCENARIO: A strong thunderstorm will have the potential to produce rainfall rates of 0.3-0.7” in 10-30 minutes. A LOOK AHEAD: Our next storm system will move into the area on Thursday with cooler temperatures in the 60’s for highs under mostly cloudy to cloudy skies. Rain showers are anticipated to develop and become scattered Thursday afternoon and evening. The threat of thunderstorms and their intensity will hinge upon temperatures/cloud cover and other factors, but best chances will be in the afternoon and early evening Thursday. Many creeks and streams are running high compared to “normal” due to recent rains or snow melt or a combination of both and should heavy rainfall develop Thursday excessive runoff may occur quickly and flash flooding is possible. Light rain showers continue likely at times overnight Thursday into Friday morning. A cloudy and cool day Friday with highs in the upper 50's to mid 60's with additional rain showers and possibly an isolated thunderstorm. The cool temperatures Friday may result in more showery conditions versus thunderstorms. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 900 PM Trace (65%) to 0.1" (30%) to 0.4" (10%) LOW Arapahoe 200 PM TO 900 PM Trace (65%) to 0.1" (30%) to 0.4" (10%) LOW Broomfield 200 PM TO 900 PM Trace (65%) to 0.1" (30%) to 0.4" (10%) LOW Denver 200 PM TO 900 PM Trace (65%) to 0.1" (30%) to 0.4" (10%) LOW Boulder 130 PM TO 900 PM Trace (75%) to 0.1" (40%) to 0.4" (15%) LOW Douglas 130 PM TO 900 PM Trace (75%) to 0.1" (40%) to 0.4" (15%) LOW Jefferson 130 PM TO 900 PM Trace (75%) to 0.1" (40%) to 0.4" (15%) LOW Foothills above 6500ft       Boulder 100 PM TO 900 PM Trace (80%) to 0.1" (40%) to 0.4" (20%) LOW Douglas 100 PM TO 900 PM Trace (80%) to 0.1" (40%) to 0.4" (20%) LOW Jefferson 100 PM TO 900 PM Trace (80%) to 0.1" (40%) to 0.4" (20%) LOW MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]