Flash Flood Prediction Program

Time: 928 AM Thu May 18, 2023 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- CLOUDY/COOL WITH RAIN SHOWERS AND SCATTERED THUNDERSTORMS CAPABLE OF PRODUCING HEAVY RAINFALL Conditions will be cloudy and cool over the District today with afternoon highs expected to only reach the lower 60’s across the plains with 50’s in the Front Range foothills. Multiple rounds of rain showers are expected with widely scattered thunderstorms this afternoon and early evening. The strength of the thunderstorms this afternoon will depend upon how much sunshine/heating is available through the first half of the day. More sun or thinning clouds equals warmer temperatures and stronger storms this afternoon, thicker clouds may result in weaker and more isolated thunderstorms. Either way there will be showers and thunderstorms that develop today with best chances for thunderstorm activity through the afternoon and early evening between 1-8pm. With all of the rain recently the ground is near saturation for many areas and thunderstorms today will have the potential to produce heavy rainfall which may result in excessive runoff and possibly flooding resulting in a high Message potential today and Messages will likely be issued by around noon. Typical showers and thunderstorms will move from W to E at 15-20mph but stronger storms may move more slowly or become right movers and track more from the NW to SE. After 8pm the chances for thunderstorms will diminish with cooling temperatures and light rain showers are expected to continue periodically overnight into early Friday morning. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce 0.1-0.5” of rain. Moderate to strong thunderstorms will have the potential to produce rainfall rates of 0.5-1.5” in 10-30 minutes. WORST CASE SCENARIO: A slower moving strong thunderstorm or a large thunderstorm complex may result in up to 2.0” of rain in 45-60 minutes. A LOOK AHEAD: Rain showers may linger into Friday morning with additional showers and widely scattered thunderstorms expected to develop in the afternoon. With ample moisture still in place thunderstorms will have the potential to produce heavy rainfall but coverage is expected to be less than today, and conditions will likely clear out quicker in the evening. Highs Friday remain in the 60’s for afternoon highs over the plains. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 1200 PM TO 800 PM 0.1" (80%) to 0.5" (50%) to 1.5" (20%) HIGH Arapahoe 1200 PM TO 800 PM 0.1" (85%) to 0.5" (55%) to 1.5" (25%) HIGH Boulder 1200 PM TO 800 PM 0.1" (85%) to 0.5" (55%) to 1.5" (25%) HIGH Broomfield 1200 PM TO 800 PM 0.1" (80%) to 0.5" (50%) to 1.5" (20%) HIGH Denver 1200 PM TO 800 PM 0.1" (80%) to 0.5" (50%) to 1.5" (20%) HIGH Douglas 1200 PM TO 800 PM 0.1" (90%) to 0.5" (60%) to 1.5" (30%) HIGH Jefferson 1200 PM TO 800 PM 0.1" (85%) to 0.5" (55%) to 1.5" (25%) HIGH Foothills above 6500ft       Boulder 1100 AM TO 800 PM 0.1" (90%) to 0.5" (60%) to 1.5" (30%) HIGH Douglas 1100 AM TO 800 PM 0.1" (90%) to 0.5" (60%) to 1.5" (30%) HIGH Jefferson 1100 AM TO 800 PM 0.1" (90%) to 0.5" (60%) to 1.5" (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]