Time: 905 AM Tue May 30, 2023 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- SLIGHTLY ABOVE NORMAL TEMPERATURES WITH ISOLATED AFTERNOON THUNDERSTORMS Temperatures will continue to run slightly above normal over the District today with afternoon highs over the plains reaching the lower 80’s with 70’s in the Front Range foothills. Normal high for Denver today is 77 degrees. Sunny skies this morning will give way to partly to mostly cloudy skies this afternoon as clouds build and thunderstorms develop. Thunderstorms will initiate over the foothills by around noon then spread out onto the plains between 1-2pm. Thunderstorm coverage will be isolated with typical storms producing light to briefly moderate rain. Storms will strengthen along and E of I-25 where there is better surface moisture with some storms possibly becoming strong to severe with brief heavy rainfall, gusty winds and hail. By 8 or 9pm the storm activity is expected to have moved to the E of the District. Generally, 1-2 rounds of storms are expected but with isolated coverage the storms will be hit or miss. Best chances for brief moderate to heavy rain will favor eastern areas of the District with lesser chances into the foothills. Upper level steering winds will result in typical storm motions from WSW to ENE at 15-20mph. Thunderstorms that form along an outflow boundary may result in some storms moving more slowly or erratically before being carried away by the upper level winds. After 8 or 9pm the thunderstorm activity is expected to have moved E of the District with dry conditions developing for the later evening and overnight period. STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce a trace to 0.2” of rain in 10-30 minutes. Strong thunderstorms will have the potential to produce rainfall rate of 0.2-0.5” in 10-30 minutes. WORST CASE SCENARIO: A slower moving or briefly stationary strong thunderstorm along an outflow boundary may result in rainfall rates of 0.3-0.7” in 10-30 minutes and up to 1.0” of rain in 45-60 minutes. A LOOK AHEAD: A slight increase in thunderstorm activity is expected Wednesday with widely scattered thunderstorms in the afternoon and early evening. Stronger storms may become severe with hail/gusty winds and carry the potential for brief heavy rain. Better chances for showers and thunderstorms on Thursday with cooler temperatures and the threat for heavy rainfall increasing. Scattered to numerous showers and thunderstorms are likely on Friday and Saturday with stronger storms capable of producing heavy rain that may lead to excessive runoff. Temperatures will be below normal and may struggle to reach 70 degrees on Friday and Saturday. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 100 PM TO 800 PM Trace (75%) to 0.2" (50%) to 0.5" (25%) MOD Arapahoe 100 PM TO 800 PM Trace (75%) to 0.2" (50%) to 0.5" (25%) MOD Boulder 100 PM TO 800 PM Trace (75%) to 0.2" (50%) to 0.5" (25%) LOW Broomfield 100 PM TO 800 PM Trace (70%) to 0.2" (40%) to 0.5" (20%) LOW Denver 100 PM TO 800 PM Trace (75%) to 0.2" (50%) to 0.5" (25%) MOD Douglas 100 PM TO 800 PM Trace (75%) to 0.2" (50%) to 0.5" (25%) MOD Jefferson 100 PM TO 800 PM Trace (70%) to 0.2" (40%) to 0.5" (20%) LOW Foothills above 6500ft       Boulder 1200 PM TO 800 PM Trace (80%) to 0.2" (50%) to 0.5" (15%) LOW Douglas 1200 PM TO 800 PM Trace (80%) to 0.2" (50%) to 0.5" (15%) LOW Jefferson 1200 PM TO 800 PM Trace (80%) to 0.2" (50%) to 0.5" (15%) 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]