Flash Flood Prediction Program

Time: 839 AM Sun July 18, 2021 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- HOT AND GENERALLY DRY PLAINS WITH ISOLATED AFTERNOON THUNDERSTORMS FAVORING THE HIGHER TERRAIN - Slight warming aloft and subtle drying will decrease the thunderstorm chances today over the District. Highs this afternoon will top out in the low to mid 90's over the plains with 80's in the Front Range foothills. - There will still be a chance for isolated afternoon thunderstorms favoring the foothills and Palmer Divide with possibly an isolated thunderstorm along the I-25 corridor mid to late afternoon. The "fly in the ointment" today is gust front activity from foothill or Palmer Divide storms... Surface moisture remains modest and the subtle drying aloft is not enough to completely eliminate the threat of heavy rain should a strong storm develop over the plains. - The most likely outcome today is isolated thunderstorm overage over the higher terrain with NW to SE steering winds keeping much if not all of the activity limited to the foothills and Palmer Divide regions. Although unlikely, if a storm were to initiate over the plains it would be later in the afternoon between 4-9pm. Plains storms should they develop will tend to be short lived and nearly stationary due to likely gust front initiation but capable of producing brief moderate to heavy rain. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.2" of rain. Although not expected, moderate to strong thunderstorms will have the potential to produce 0.2-0.6" in 10-30 minutes. WORST CASE SCENARIO: A stationary strong thunderstorm will have the potential to produce up to 1.2" of rain in 45-60 minutes. A LOOK AHEAD: Generally dry conditions expected over on Monday with any storm activity limited to the higher terrain. Tuesday chances for thunderstorms return to the District and look to peak on Wednesday with lesser chances Thursday and Friday. Monday/Tuesday thunderstorms will have the potential to produce brief heavy rainfall. Temperatures through the week will continue to run in the 90's over the plains. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 400 PM TO 900 PM Trace (30%) to 0.2" (15%) to 0.6" (5%) LOW Arapahoe 400 PM TO 900 PM Trace (30%) to 0.2" (15%) to 0.6" (5%) LOW Broomfield 400 PM TO 900 PM Trace (30%) to 0.2" (15%) to 0.6" (5%) LOW Denver 400 PM TO 900 PM Trace (30%) to 0.2" (15%) to 0.6" (5%) LOW Boulder 300 PM TO 900 PM Trace (40%) to 0.2" (20%) to 0.6" (5%) LOW Douglas 300 PM TO 900 PM Trace (40%) to 0.2" (20%) to 0.6" (5%) LOW Jefferson 300 PM TO 900 PM Trace (40%) to 0.2" (20%) to 0.6" (5%) LOW Foothills above 6500ft       Boulder 100 PM TO 900 PM Trace (60%) to 0.2" (30%) to 0.6" (10%) LOW Douglas 100 PM TO 900 PM Trace (60%) to 0.2" (30%) to 0.6" (10%) LOW Jefferson 100 PM TO 900 PM Trace (60%) to 0.2" (30%) to 0.6" (10%) 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]