Flash Flood Prediction Program

Cooler and cloudy to start the day as a disturbance is poised to move over the District this afternoon, through the evening with a slight chance for some overnight showers/isolated thunderstorms. Currently temperatures are in the mid 60’s with highs expected in the mid to upper 70’s this afternoon. Dew points are currently elevated, in the mid 50’s and will likely remain if not increase as the day progresses.

Showers and thunderstorms will likely initiate along the higher terrain by midday today. The best chance for storm activity within the District will be from 1pm through midnight, with a few lingering showers through the overnight, tapering off between 2-4am. Multiple rounds of showers/thunderstorms will be possible this afternoon and evening with a good chance of isolated heavy rainfall resulting in a HIGH chance for Message 1’s to be issued.

Storm motions will be the typical W/SW to E/NE motions between 5-10mph with some erratic storm movement likely off outflow boundaries. Storms may also contain large hail, strong winds, frequent cloud-to-ground lightning and possible an isolated land spout/weak tornado, mainly for eastern portions of the District.

STORM RAINFALL POTENTIAL AND DURATION: Typical rain showers and thunderstorms will produce a 0.25-0.50” total, in 10-30 minutes. A moderate to strong thunderstorm will produce 0.50-1.50” total, in 10-30 minutes.

WORST CASE SCENARIO: A strong thunderstorm anchors off an outflow boundary, or training of thunderstorms could potentially produce up to 2.4” total in 45-60 minutes.

A LOOK AHEAD: Similar conditions remain in place Friday, although upper-level shifts northwesterly, leading to slightly less chances for heavy rainfall as storms expected to increase in speed during the day and into the evening Friday. Currently at least a MODERAT threat for Heavy rainfall will be possible tomorrow. This weekend will remain active with afternoon and evening showers/thunderstorm chances both Saturday and Sunday. However, the threat of heavy rainfall will be isolated, likely keeping a LOW chance for Message 1’s to be issued.

Location	Prime Time	30-Minute Rainfall and % Probability	Message Potential
Plains
Adams	100 PM TO 1159 PM	0.25" (80%) to 0.5" (60%) to 1.5" (30%)	HIGH
Arapahoe	100 PM TO 1159 PM	0.25" (80%) to 0.5" (60%) to 1.5" (30%)	HIGH
Boulder	100 PM TO 1159 PM	0.25" (80%) to 0.5" (60%) to 1.5" (30%)	HIGH
Broomfield	100 PM TO 1159 PM	0.25" (80%) to 0.5" (60%) to 1.5" (30%)	HIGH
Denver	100 PM TO 1159 PM	0.25" (80%) to 0.5" (60%) to 1.5" (30%)	HIGH
Douglas	100 PM TO 1159 PM	0.25" (80%) to 0.5" (60%) to 1.5" (30%)	HIGH
Jefferson	100 PM TO 1159 PM	0.25" (80%) to 0.5" (60%) to 1.5" (30%)	HIGH
Foothills above 6500ft
Boulder	100 PM TO 1159 PM	0.25" (90%) to 0.5" (70%) to 1.5" (30%)	HIGH
Douglas	100 PM TO 1159 PM	0.25" (90%) to 0.5" (70%) to 1.5" (40%)	HIGH
Jefferson	100 PM TO 1159 PM	0.25" (90%) to 0.5" (70%) to 1.5" (40%)	HIGH

MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS.