Colorado Monsoon Season and Lightning: When the Front Range Is Most at Risk

Colorado’s monsoon season usually starts around the second week of July and winds down by late August, though it can run into October. It’s the peak of a summer lightning season that starts earlier on the Front Range. On an average July day, the National Weather Service counts about 5,350 lightning flashes across the state. If you own a building in Colorado, mid-summer is when lightning protection gets tested, so late spring is the time to check it.

What the Colorado monsoon actually is

The monsoon isn’t a single storm. It’s a seasonal shift in wind. NWS Grand Junction explains that as summer goes on, high pressure moves and turns the winds, letting moisture flow north from the Pacific and the Gulf of California into the Southwest. The Colorado Climate Center at CSU describes the same pattern. It ramps up in July and lasts through August. You can see it arrive when dewpoints climb from the teens and 20s in June into the 50s by August.

NWS Grand Junction also describes how it behaves. It comes in bursts, when moisture and cooler air aloft produce rounds of thunderstorms, and breaks, when high pressure shuts off the moisture. A week of daily afternoon storms followed by a dry week is normal monsoon behavior.

Front Range vs Western Slope

The monsoon doesn’t hit the whole state the same way. The Colorado Climate Center’s records show:

Region	Wettest period	Monsoon effect
Western Slope and southwest Colorado	July, August, September	Strongest. The monsoon drives the wettest months
Denver and the Front Range	Spring maximum, with a secondary summer peak	Moderate. It adds to an existing summer storm pattern
Northeast plains	Early summer	Minimal

So on the Front Range, the monsoon extends and intensifies a lightning season that has already started with spring and early-summer storms. It doesn’t create one. Colorado’s Lightning Safety Awareness Week is held the last full week of June every year, ahead of the busiest stretch.

Colorado lightning by the numbers

These figures come from NWS Pueblo’s statewide comparison unless noted:

Measure	Colorado figure
Cloud-to-ground flashes, average year	About 500,000
Average flash density	4.8 flashes per km² per year (2009–2018)
National rank, number of flashes	19th (2009–2018)
National rank, flash density	32nd (2009–2018)
National rank, lightning deaths	3rd (2006–2024)
Average casualties per year (since 1980)	2 deaths, 12 injuries
County with most casualties	El Paso County
Flashes on an average July day	About 5,350 (NWS, via KUNC)

The gap between those rankings is the story. Colorado sees a middling amount of lightning for its size but ranks near the top for deaths. NWS Denver/Boulder explains why: most Colorado lightning deaths and injuries happen in the afternoon, when storms form and people are outside, hiking, golfing, ranching and working on job sites. Quite a few happen with little or no rain falling. Lightning can strike more than 10 miles from the rain area of a storm.

Lightning and wildfire

NWS Denver/Boulder notes that lightning starts around half of Colorado’s forest and rangeland wildfires, and that the state averages around 2,500 wildfires a year. Many lightning-caused fires start with little or no rain, and the storms often bring gusty winds that spread them.

For a property owner in the foothills or on a rangeland parcel, a strike on the building is only part of the risk. A strike that sets the grass or a tree on fire near the house is a concern too, and so is the storm that knocks out power while it happens.

What this means for buildings

People are the reason for the safety rules. Buildings carry the cost. During monsoon and summer storm season, Colorado buildings face:

• Direct strikes on the highest points: chimneys, ridges, rooftop units, flagpoles, silos, antennas.
• Strikes on nearby trees and power lines that send surges in through utilities.
• Ignition in attics, roof decks and hay or feed storage.
• Repeat exposure. The same exposed building on a ridge sees storm after storm in a burst week.

A lightning protection system gives a strike a planned path to ground. The Lightning Protection Institute describes it as five parts working together: strike termination devices, conductors, grounding electrodes, bonding, and surge protection at every service entrance. Our article on why commercial lightning protection matters for Colorado businesses covers the commercial side. For homes, see our residential lightning protection page.

Pre-season checklist for May and June

If you already have a system, walk it before the storms start:

• Air terminals. All still upright and attached? Any bent by snow, hail or roof work?
• Roof work since last summer. LPI calls for the system to be reviewed after re-roofing, additions or new equipment, because roof work can disconnect it.
• New rooftop equipment. Solar, HVAC units, antennas or dishes added since the system went in need to be bonded.
• Down conductors. Still continuous to grade, and guarded where they can be hit?
• Grounds. Any connections at grade dug up, cut by landscaping or buried under new concrete?
• Surge protection. Panel surge devices have status indicators. Check them, since LPI notes these devices can sacrifice themselves over time.
• Paperwork. Know when the last full inspection was. NFPA 780 and LPI-175 recommend a visual check every year and a full inspection with testing every 3 to 5 years.

If you don’t have a system, late spring is the time to get an assessment. That way the work is done before July storms start interrupting roof work. Our post on when to have your system re-inspected covers what triggers a re-inspection.

Talk to us before July

Site Safe Lightning Protection works on lightning protection and inspections for homes, commercial buildings and oil and gas facilities. If you want a system checked or quoted before monsoon season, contact Site Safe Lightning Protection.