Flash Flood Prediction Program

Message 2’s (NWS Flood/Flash Flood Watch) have been issued for the entire District and will be valid from 4:00 PM until midnight tonight. Thunderstorms are expected to develop over the next 1-3 hours over the District and continue well into the evening with multiple rounds of showers and thunderstorms possible. Should thunderstorm activity persist past midnight Message 2’s may be extended into the early morning hours on Tuesday.

Thunderstorms that develop later this afternoon and evening have ample moisture to work with and will be very capable of producing heavy rainfall that may lead to excessive runoff and flash flooding within the District. Storms will be relatively slow moving at 10-15mph allowing for extended periods of heavy rain.

Prime time for thunderstorms will be from 5:00 PM until 11:30 PM. Heavy rainfall will be the primary threat from thunderstorms today, but large hail and gusty winds is also possible from stronger storms. The stronger thunderstorms may favor areas E of I-25 where surface moisture is more abundant.

STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce rainfall rates of 0.2-0.8” in 10-30 minutes. Strong thunderstorms will have the potential to produce rainfall rates of 0.8-2.0” of rain in 10-30 minutes.

WORST CASE SCENARIO: A slow moving strong thunderstorm or a large thunderstorm complex may result in up to 3.5” of rain in 60-90 minutes.

County	Message	Valid Times	Prime Time
Boulder County	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Jefferson County	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Broomfield County	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Douglas County	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Adams County	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Denver County	2	400 PM TO 1159 PM	500 PM TO 1130 PM
DIA	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Arapahoe County	2	400 PM TO 1159 PM	500 PM TO 1130 PM
the City of Aurora	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Arvada	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Wheat Ridge	2	400 PM TO 1159 PM	500 PM TO 1130 PM
Lakewood	2	400 PM TO 1159 PM	500 PM TO 1130 PM

County-specific Quantitative Precipitation Outlook	Precipitation Time	30-Minute Rainfall and % Probability	Message Potential
Plains
Adams	430 PM TO 1159 PM	0.5" (80%) to 1" (50%) to 2" (30%)	ISSUED
Arapahoe	430 PM TO 1159 PM	0.5" (80%) to 1" (50%) to 2" (30%)	ISSUED
Boulder	430 PM TO 1159 PM	0.5" (75%) to 1" (50%) to 2" (25%)	ISSUED
Broomfield	430 PM TO 1159 PM	0.5" (75%) to 1" (50%) to 2" (25%)	ISSUED
Denver	430 PM TO 1159 PM	0.5" (80%) to 1" (50%) to 2" (30%)	ISSUED
Douglas	430 PM TO 1159 PM	0.5" (75%) to 1" (50%) to 2" (25%)	ISSUED
Jefferson	430 PM TO 1159 PM	0.5" (75%) to 1" (50%) to 2" (25%)	ISSUED
Foothills above 6500ft
Boulder	Current TO 1159 PM MON	0.5" (75%) to 1" (50%) to 2" (25%)	ISSUED
Douglas	Current TO 1159 PM MON	0.5" (75%) to 1" (50%) to 2" (25%)	ISSUED
Jefferson	Current TO 1159 PM MON	0.5" (75%) to 1" (50%) to 2" (25%)	ISSUED

MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS.