Flash Flood Prediction Program

Time: 922 AM Fri July 15, 2022 Forecaster: Justin Brooks ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- THUNDERSTORMS WITH THE POTENTIAL TO PRODUCE HEAVY RAINFALL THIS AFTERNOON/EVENING - Temperatures will back off today but remain on the warm side with highs reaching the low to mid 90's over the plains ahead of cloud cover and storm activity. Subtropical monsoon moisture will stream overhead and with ample surface moisture there will be a good chance for afternoon and early evening rain showers and thunderstorms. Some storms may become strong with the potential to produce heavy rainfall that may lead to excessive runoff and possibly flash flooding. - Initial storm development along the higher terrain will likely begin by around noon with the best chance for rain showers/thunderstorms over the plains between 1-9pm. Storm motions will be from W to E between 10-15mph, however a gust front, or outflow boundary has the potential to initiate storms that anchor in place for an extended period of time or move more slowly. Storms are expected to strengthen along and E of the I-25 corridor possibly becoming severe over the plains. - NWS Flash Flood Watch is in effect for Boulder County above 6,000ft from 11:00 AM to 9:00 PM to account for the Calwood Burn area just north of the District. Locations outside of recent burn areas, including the Four Mile burn area the flash flood threat will be lower. The MHFD will issue a Message 2 Boulder County to sync with the NWS time frame. Message 1's will be issued for the remaining Counties but will become valid at noon or 1pm just ahead of storm development. STORM RAINFALL POTENTIAL AND DURATION: Typical rain showers and weak thunderstorms will produce a trace to 0.5" of moisture in 30-60 minutes. 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 large thunderstorm complex or a nearly stationary strong thunderstorm may result in up to 2.5" of rain in 45-75 minutes. A LOOK AHEAD: Cooler tomorrow with a continued chance for afternoon and early evening rain showers/isolated thunderstorms. The upper-level pattern will shift from SW to NW which will add more variability for storm development, however a low threat for moderate to brief heavy rain will likely remain. Sunday starts to warm up significantly with highs reaching around 100 degrees along with generally dry conditions. Similar conditions Monday with hot temperatures and a very slight chance for scattered high-based afternoon/eve rain showers/isolated thunderstorms. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 900 PM 0.1" (90%) to 0.5" (60%) to 1.5" (20%) HIGH Arapahoe 200 PM TO 900 PM 0.1" (90%) to 0.5" (60%) to 1.5" (20%) HIGH Broomfield 200 PM TO 900 PM 0.1" (90%) to 0.5" (60%) to 1.5" (20%) HIGH Denver 200 PM TO 900 PM 0.1" (90%) to 0.5" (60%) to 1.5" (20%) HIGH Boulder 100 PM TO 900 PM 0.1" (90%) to 0.5" (60%) to 1.5" (20%) HIGH Douglas 100 PM TO 900 PM 0.1" (90%) to 0.5" (60%) to 1.5" (20%) HIGH Jefferson 100 PM TO 900 PM 0.1" (90%) to 0.5" (60%) to 1.5" (20%) HIGH Foothills above 6500ft       Boulder 1200 PM TO 900 PM 0.1" (95%) to 0.5" (65%) to 1.5" (20%) HIGH Douglas 1200 PM TO 900 PM 0.1" (95%) to 0.5" (65%) to 1.5" (20%) HIGH Jefferson 1200 PM TO 900 PM 0.1" (95%) to 0.5" (65%) to 1.5" (20%) 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]