Colorado weather: Afternoon thunderstorms threaten flooding, large hail, strong winds

Afternoon thunderstorms moving across Colorado on Thursday could bring flash floods, large hail and strong winds, according to the National Weather Service.

Widespread showers and thunderstorms are forecast across the mountains today, and will gradually spread into the Interstate 25 corridor and plains this afternoon and evening, NWS forecasters said in a hazardous weather alert Thursday.

Thunderstorms will bring heavy rain and possible flash flooding, especially over alpine burn scars, according to the hazardous weather outlook.

In areas where fire burns hot or long enough — including burn scars left by the Cameron Peak fire in Jackson and Larimer counties, the East Troublesome fire in Grand and Larimer counties, the Williams Fork fire in Grand County and the Alexander Mountain fire in Larimer County — the soil develops a water-repellant layer that reacts like rain on pavement, weather officials said.

Rainfall that would normally be absorbed by the forest canopy and loose tree litter on the ground instead runs off, starting flash floods during periods of heavy rain.

“If you can look uphill from where you are and see a burnt-out area, you are at risk,” NWS meteorologists said.

Gusty winds and hail are the main threats over Denver and east of the metro area, forecasters said in the hazardous weather outlook.

Expected wind speeds and hail sizes were not available Thursday morning, but NWS categorizes “strong” winds as 60 mph or more and “large” hail as hail from 1 inch to 1 3/4 inch in diameter — between the size of quarters and golf balls.

Storms will be most active in Denver between 5 p.m. and midnight, and strongest across the Eastern Plains between 2 p.m. and midnight, according to NWS meteorologists.

Denver will see temperature highs of 86 degrees Thursday before dropping into the low 60s overnight, according to forecasters.

Severe weather will continue throughout the week in the mountains and upper foothills, but the metro area can expect only mild afternoon showers through the weekend, forecasters said.