Flash Flood Prediction Program

Time: 947 AM Fri June 17, 2022 Forecaster: Brad Simmons ------------------------- Heavy Precipitation Outlook Flash Flood Prediction Program ------------------------- HOT/HAZY WITH AFTERNOON/EVENING THUNDERSTORM ACTIVITY FAVORING THE FOOTHILLS - The warming trend will reach a peak today with afternoon high temperatures topping out in the mid 90's to around 100 degrees over the plains. Foothills will be cooler in the 80's. Hazy conditions will continue as southerly upper level winds import more smoke from wildfires over AZ/NM. The southerly upper level winds are also importing moisture in the mid and upper levels but the majority of the moisture will remain over the mountainous areas of the state today, but will lead to better storm chances over the District this weekend increasing the heavy rainfall threat. - Shower and thunderstorm activity will develop W of the District over the mountains and higher foothills as early as noon. Outflow from initial thunderstorm activity over the foothills pushing eastward will be the most likely culprit for storm development over the plains. By 1-2pm isolated thunderstorms become possible over the plains with chances going through sunset. Storm coverage will be isolated lower elevations favoring areas along and W of I-25 and scattered over the foothills, favoring Boulder County. With ample surface moisture the storms that develop today, although far and few between over lower elevations will be capable of producing brief heavy rainfall. - Upper level steering winds from S to N at 20-25mph will be responsible for keeping most of the storm activity over the higher terrain as there will be little eastward progression. The relatively fast storm motions will help to reduce point rainfall amounts from a single storm cell, but training of thunderstorm cells would produce extended periods of moderate to heavy rainfall that may lead to excessive runoff resulting in a LOW Message potential today over the majority of the District. STORM RAINFALL POTENTIAL AND DURATION: Rain showers and weak thunderstorms will produce a trace to 0.3" of rainfall. Moderate to strong thunderstorms will have the potential to produce rainfall rates of 0.3-0.9" in 10-30 minutes. WORST CASE SCENARIO: Training of strong thunderstorm cells may result in up to 1.6" of rain in 45-60 minutes. A LOOK AHEAD: Thunderstorm activity will be increasing over the weekend as temperatures begin to lower into early next week. Ample moisture at the surface and aloft will result in thunderstorms that develop over the coming days having the potential to produce brief heavy rainfall. Temperatures on Saturday remain above seasonal averages in the low and mid 90's over the plains and continue to cool Sunday with readings in the upper 80's to lower 90's. LOCATION PRIME TIME 30-Minute Rainfall and % Probability Message Potential Plains       Adams 200 PM TO 1000 PM Trace (60%) to 0.3" (30%) to 0.6" (15%) LOW Arapahoe 200 PM TO 1000 PM Trace (60%) to 0.3" (30%) to 0.6" (15%) LOW Denver 200 PM TO 1000 PM Trace (60%) to 0.3" (30%) to 0.6" (15%) LOW Boulder 100 PM TO 1000 PM Trace (75%) to 0.3" (40%) to 0.6" (20%) LOW Broomfield 100 PM TO 1000 PM Trace (65%) to 0.3" (30%) to 0.6" (15%) LOW Douglas 100 PM TO 1000 PM Trace (75%) to 0.3" (40%) to 0.6" (20%) LOW Jefferson 100 PM TO 1000 PM Trace (75%) to 0.3" (40%) to 0.6" (20%) LOW Foothills above 6500ft       Boulder 1200 PM TO 1000 PM Trace (100%) to 0.3" (75%) to 0.6" (40%) MOD Douglas 1200 PM TO 1000 PM Trace (80%) to 0.3" (50%) to 0.6" (30%) LOW Jefferson 1200 PM TO 1000 PM Trace (90%) to 0.3" (60%) to 0.6" (35%) 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]