From National Weather Service:

...FLASH FLOOD WATCH NORTHERN FRONT RANGE FOOTHILLS NOON UNTIL
10 PM MDT THIS EVENING...

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTHEAST AND NORTH CENTRAL
COLORADO.

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WITH LOCALLY HEAVY RAINFALL AND POSSIBLE
SEVERE WEATHER ARE EXPECTED TO DEVELOP ACROSS THE REGION THIS
AFTERNOON AND CONTINUE INTO THE EVENING.  STORMS ARE FIRST EXPECTED
TO FIRE OVER THE MOUNTAINS AND FOOTHILLS BY THE NOON HOUR...AND THEN
SPREAD AND DEVELOP EASTWARD ACROSS THE PLAINS THIS AFTERNOON AND
EVENING.  THE STRONGER STORMS WILL BE CAPABLE OF PRODUCING LARGE
HAIL...WIND GUSTS UP TO 60 MPH...AND 1 TO 2 INCHES OF RAIN IN AN
HOUR OR LESS.

STORMS ARE EXPECTED TO BE SLOW MOVING...AND LOCALLY HEAVY RAIN WILL
BRING A THREAT OF FLASH FLOODING ESPECIALLY IN THE RECENT BURN SCARS
ACROSS THE FRONT RANGE FOOTHILLS.

A MORE MOIST AND UNSTABLE ENVIRONMENT IN THE WAKE OF A WEAK COLD
FRONT WILL BRING THE THREAT OF SEVERE WEATHER AND HEAVY RAINFALL.