Flash Flood Prediction Program

A minimal change to the overall pattern as westerly flow aloft continues to dominate over the region. Dew points have remained in the 50’s and will likely hold through the rest of the day. The best chance for storm development within the District will be between 2-10pm. Storm motions will once again be W to E between 10-20mph, effectively limiting any point rainfall amounts. However, a few storms could produce gust fronts, with additional storms forming along these gust fronts inside the District. These storms will have the potential to produce longer lasting heavy rainfall as they will likely stall out over an area for an extended period. Training of thunderstorm cells is another potential culprit for longer duration moderate to heavy rainfall that may lead to excessive runoff and flash flooding. Strong thunderstorms may also contain gusty winds and large hail.

Multiple rounds of showers and thunderstorms will move across the District through the afternoon and evening, with the strongest storms likely during the first round with storms decreasing in intensity as the evening progresses. Skies will clear late this evening with overnight lows in the upper 50’s to low 60’s on the plains with low to mid 50’s along the foothills.

STORM RAINFALL POTENTIAL AND DURATION: Typical showers/weak thunderstorms will produce a 0.05-0.25” total, in 10-30 minutes. A moderate shower/isolated thunderstorm will produce 0.25-0.75” total in 10-30 minutes. Strong thunderstorms will produce 0.75-1.25” total in 10-30 minutes.

WORST CASE SCENARIO: A stronger, stalled out thunderstorm is able to develop and will have the potential to produce up to 2.40” total, in 45-60 minutes.

A LOOK AHEAD: A slight decrease in overall moisture in the area tomorrow will slightly decrease the heavy rainfall threat. Storm chances will be similar to today, between 2-10pm with west to east storm movements between 15-25mph which once again should help limit point rainfall amounts. At least a low chance will likely remain for Message 1’s to be issued. Less chances for afternoon/eve showers/thunderstorms Friday with slightly warmer high temperatures around 90 degrees.

Location	Prime Time	30-Minute Rainfall and % Probability	Message Potential
Plains
Adams	200 PM TO 1000 PM	0.25" (65%) to 0.75" (35%) to 1.25" (15%)	MOD
Arapahoe	200 PM TO 1000 PM	0.25" (60%) to 0.75" (30%) to 1.25" (10%)	MOD
Boulder	200 PM TO 1000 PM	0.25" (70%) to 0.75" (40%) to 1.25" (20%)	HIGH
Broomfield	200 PM TO 1000 PM	0.25" (65%) to 0.75" (35%) to 1.25" (15%)	MOD
Denver	200 PM TO 1000 PM	0.25" (60%) to 0.75" (30%) to 1.25" (10%)	MOD
Douglas	200 PM TO 1000 PM	0.25" (60%) to 0.75" (30%) to 1.25" (10%)	MOD
Jefferson	200 PM TO 1000 PM	0.25" (65%) to 0.75" (35%) to 1.25" (15%)	MOD
Foothills above 6500ft
Douglas	200 PM TO 1000 PM	0.25" (60%) to 0.75" (30%) to 1.25" (10%)	MOD
Jefferson	200 PM TO 1000 PM	0.25" (70%) to 0.75" (40%) to 1.25" (15%)	HIGH
Boulder	100 PM TO 900 PM	0.25" (75%) to 0.75" (50%) to 1.25" (20%)	HIGH

MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS.