Flash Flood Prediction Program

Time: 523 PM Thu May 11, 2023 Forecaster: Brad Simmons ------------------------- Internal Message Status Flash Flood Prediction Program ------------------------- MESSAGE 2'S (NWS Flood/Flash Flood Watch) REMAINS VALID/RAIN SHOWERS TO CONTINUE INTO THE EVENING/OVERNIGHT Message 2’s (NWS Flood/Flash Flood Watch) will remain valid until 6:00 AM Friday as rain showers will continue to fall over the District. Rainfall totals from roughly sunrise this morning until now range from 0.5-1.5” over NW portions of the District with 1.0-2.5” or more for central/eastern and southern areas and has resulted in creeks and streams running high resulting in minor flooding for many areas with isolated areas of moderate impact. Rainfall rates appear to have peaked, and intensities have been backing off over the past couple hours and creeks and streams should begin to subside slightly but remain elevated as the ground is saturated and additional rainfall will easily result in runoff. Rainfall intensities peaked earlier today in the 0.5-1.0” in 60 minute range and are now in the 0.1-0.3” in 60 minute range and this type of intensity is expected to continue for the duration of the event with isolated higher rates of 0.2-0.6” in 60 minutes under the heavier showers. With temperatures in the mid 40’s to lower 50’s the threat for thunderstorms is very low but not zero. Should a weak thunderstorm develop higher rainfall rates are possible and could exacerbate runoff already occurring and result in flash flooding. There could be a few lulls in the precipitation this evening only to fill in again overnight with some snow possible for higher elevations at or above the 8,000ft level. Rain showers are expected to continue into tomorrow morning before starting to break up later in the morning or during the afternoon as the slow moving low pressure system over SE Colorado continues to churn and stream moisture into the area. STORM RAINFALL POTENTIAL AND DURATION: Light rain showers will produce rainfall rates of 0.1-0.3" in 60 minutes. Moderate to heavy non-thunderstorm rain showers will produce rainfall rates of 0.3-0.8" in 60 minutes. WORST CASE SCENARIO: A weak to briefly moderate thunderstorm is able to develop in a cold air mass with the potential to produce heavy rainfall of 0.4-1.2" in 10-30 minutes. COUNTY MESSAGE VALID TIMES PRIME TIME Lakewood 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Wheat Ridge 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Arvada 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY the City of Aurora 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Arapahoe County 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY DIA 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Denver County 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Adams County 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Douglas County 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Broomfield County 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Jefferson County 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY Boulder County 2 Current TO 600 AM FRIDAY Current TO 600 AM FRIDAY County-specific Quantitative Precipitation Outlook PRECIPITATION TIME 60-Minute Rainfall and % Probability Message Potential Plains       Adams Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Arapahoe Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Boulder Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Broomfield Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Denver Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Douglas Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Jefferson Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Foothills above 6500ft       Boulder Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Douglas Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED Jefferson Current TO 600 AM FRI 0.1" (100%) to 0.3" (75%) to 0.8" (25%) ISSUED MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS. MHFD Flood Prediction Center: 303-458-0789    F2P2 Website [http://udfcd.org/Flash+Flood+Prediction+Program]