Time: 947 AM Tue June 18, 2019 Forecaster: Alan Smith

Heavy Precipitation Outlook
Flash Flood Prediction Program

COOLER THAN AVERAGE WITH NUMEROUS AFTERNOON THUNDERSTORMS CAPABLE OF HEAVY RAINFALL
-Deep moisture remains in place across the District today, while an active upper level pattern will result in widespread thunderstorm activity once again. Areas of low clouds and fog/drizzle this morning will give way to partial clearing by early afternoon with high temperatures remaining cooler than average in the upper 60s to low/mid 70s on the plains.
-Another upper level disturbance will arrive early this afternoon, bringing cooler air aloft that will allow for the atmosphere to destabilize. Thunderstorms will develop over the foothills before spreading onto the plains between roughly 1-3pm with additional storms possible through early/mid evening.
-Storms will be moving a little faster than previous days to the E/SE at 12-17mph, but with dewpoints well into the 50s, stronger storms that develop will produce heavy rainfall. In addition, there will be some potential for stronger storms to temporarily stall along outflow or wind convergence boundaries. The most widespread coverage of thunderstorms will occur this afternoon, but additional isolated thunderstorms will be possible through early evening.
STORM RAINFALL POTENTIAL AND DURATION: Weak to moderate thunderstorms will produce rainfall amounts of 0.2-0.5" in 10-30 minutes. Strong thunderstorms will be capable of producing rainfall of 0.5-1.5" in 10-30 minutes.

WORST CASE SCENARIO: A strong thunderstorm stalls along a convergence boundary, or training of thunderstorm cells occurs, resulting in heavy rainfall of up to 3.0" in 90-120 minutes.

A LOOK AHEAD: Wednesday will feature warmer temperatures and gradual drying, but enough upper level energy and lingering low level moisture will remain for isolated afternoon thunderstorms, with the potential for moderate to heavy rain if a stronger thunderstorm manages to develop. Low level moisture will decrease on Thursday, but another disturbance will move into Northern Colorado which will keep isolated thunderstorm chances going over the District, although the heavy rainfall threat will decrease. On Friday, an unseasonably cold trough of low pressure will approach from the northwest, resulting in a good chance of thunderstorms across the District with heavy rainfall and severe weather possible.

Location Prime Time 30-Minute Rainfall
and % Probability
Message
Potential
Plains      
Adams 200 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Arapahoe 200 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Broomfield 200 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Denver 200 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Boulder 130 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Douglas 130 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Jefferson 130 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Foothills above 6500ft      
Boulder 1230 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Douglas 1230 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
Jefferson 1230 PM TO 900 PM
0.1" (95%) to 0.5" (50%) to 1.5" (25%) HIGH
MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS.