Time: 900 AM Sat July 4, 2020 Forecaster: Brad Simmons

Heavy Precipitation Outlook
Flash Flood Prediction Program

SCATTERED AFTERNOON THUNDERSTORMS WITH HEAVY RAIN POSSIBLE
-Abundant surface moisture and daytime heating in tandem with a passing upper level disturbance will result in scattered thunderstorms this afternoon and early evening over the District. Temperatures today are expected to be a degree or two cooler than yesterday due to additional cloud cover with highs in the upper 80's to lower 90's over the plains.
-Thunderstorms will first develop over the foothills by around noon or before and then move into the I-25 corridor between 1-2pm. A round or two of storms is then expected move through into the early evening. Typical storms today will produce moderate to brief heavy rainfall with strong thunderstorms capable of producing extended periods of heavy rainfall which may lead to excessive runoff and possibly flash flooding. Strong storms may also contain large hail, frequent cloud-to-ground lightning and gusty winds.
-Thunderstorms will be slow moving from SW to NE at 10mph or less. Strong thunderstorms may remain nearly stationary or move erratically along outflow boundaries/gust fronts. Thunderstorm activity is expected to diminish this evening around sunset with a few lingering light showers possible past dark.
STORM RAINFALL POTENTIAL AND DURATION: Typical weak to moderate thunderstorms will produce 0.1-0.5" in 10-30 minutes. Strong thunderstorms will have the potential to produce 0.5-1.3" in 10-30 minutes.

WORST CASE SCENARIO: A large thunderstorm complex or a nearly stationary strong thunderstorm may produce up to 2.5" in 60 minutes or less.

A LOOK AHEAD: Moisture begins to decrease on Sunday but there will still be a good chance for afternoon thunderstorms with widely scattered coverage and storms a bit weaker than today but still capable of producing heavy rainfall. Temperatures on Sunday will continue to run in the upper 80's to lower 90's for highs over the plains.

Location Prime Time 30-Minute Rainfall
and % Probability
Message
Potential
Plains      
Adams 200 PM TO 700 PM
0.1" (80%) to 0.5" (40%) to 1.3" (20%) HIGH
Arapahoe 200 PM TO 700 PM
0.1" (80%) to 0.5" (40%) to 1.3" (20%) HIGH
Broomfield 200 PM TO 700 PM
0.1" (80%) to 0.5" (40%) to 1.3" (20%) HIGH
Denver 200 PM TO 700 PM
0.1" (80%) to 0.5" (40%) to 1.3" (20%) HIGH
Boulder 100 PM TO 700 PM
0.1" (80%) to 0.5" (40%) to 1.3" (20%) HIGH
Douglas 100 PM TO 700 PM
0.1" (80%) to 0.5" (40%) to 1.3" (20%) HIGH
Jefferson 100 PM TO 700 PM
0.1" (80%) to 0.5" (40%) to 1.3" (20%) HIGH
Foothills above 6500ft      
Boulder 1200 PM TO 700 PM
0.1" (90%) to 0.5" (40%) to 1.3" (15%) HIGH
Douglas 1200 PM TO 700 PM
0.1" (90%) to 0.5" (40%) to 1.3" (15%) HIGH
Jefferson 1200 PM TO 700 PM
0.1" (90%) to 0.5" (40%) to 1.3" (15%) HIGH
MONITOR NATIONAL WEATHER SERVICE FOR SEVERE WEATHER STATEMENTS.