Flash Flood Prediction Program

Strong to severe thunderstorms with large hail and moderate to heavy rainfall with multiple tornado warned storms by the NWS moved through the District this afternoon. The strong to severe thunderstorms have moved to the NE out of the District as of 6:00pm leaving a cool air mass in their wake with temperatures in the 50’s plains and 40’s foothills.

The threat for strong thunderstorms with hail and heavy rainfall is diminishing now the atmosphere has been churned and temperatures are cooling leaving scattered to widespread rain showers and weak to moderate thunderstorms to continue into the evening and overnight period. With a moist atmosphere in place even weak to moderate thunderstorms will be capable of producing heavy rainfall this evening keeping the Message 1’s valid.

There is a chance that Message 1’s may need to be extended as we approach midnight into Thursday morning depending upon how conditions play out over the next 4-6 hours. Now that the ground is becoming saturated in some locations that experienced heavy rain and hail earlier today it may not take as much rain to produce excessive runoff this evening and overnight.

STORM RAINFALL POTENTIAL AND DURATION: Rain showers will produce a trace to 0.2" in 10-30 minutes. Weak thunderstorms will have the potential to produce 0.2-0.4" in 10-30 minutes. Moderate to briefly strong thunderstorms will have the potential to produce rainfall rates of 0.4-1.0" in 10-30 minutes.

WORST CASE SCENARIO: A slower moving or nearly stationary thunderstorm or training of thunderstorm cells has the potential to produce up to 2.0" 45-60 minutes.

County	Message	Valid Times	Prime Time
Denver County	1	100 PM TO 1159 PM	Current TO 1130 PM
Douglas County	1	100 PM TO 1159 PM	Current TO 1130 PM
Adams County	1	100 PM TO 1159 PM	Current TO 1130 PM
Broomfield County	1	100 PM TO 1159 PM	Current TO 1130 PM
Jefferson County	1	100 PM TO 1159 PM	Current TO 1130 PM
Boulder County	1	100 PM TO 1159 PM	Current TO 1130 PM
DIA	1	100 PM TO 1159 PM	Current TO 1130 PM
Arapahoe County	1	100 PM TO 1159 PM	Current TO 1130 PM
the City of Aurora	1	100 PM TO 1159 PM	Current TO 1130 PM
Arvada	1	100 PM TO 1159 PM	Current TO 1130 PM
Wheat Ridge	1	100 PM TO 1159 PM	Current TO 1130 PM
Lakewood	1	100 PM TO 1159 PM	Current TO 1130 PM

County-specific Quantitative Precipitation Outlook	Precipitation Time	30-Minute Rainfall and % Probability	Message Potential
Plains
Adams	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Arapahoe	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Boulder	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Broomfield	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Denver	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Douglas	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Jefferson	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Foothills above 6500ft
Boulder	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Douglas	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED
Jefferson	Current TO 1159 PM WED	0.1" (100%) to 0.4" (50%) to 1" (15%)	ISSUED

MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS.