September is here, and political ad season is truly upon us.

Almost 70 percent of the nearly $56 million in ad spending at Colorado TV stations will come this month through Nov. 4. That’s just traditional TV ads, not those running on cable or satellite programs, which don’t have to report spending to the Federal Communication Commission.

Through Friday, Aug. 29, contracts for political ads total almost 545 hours or nearly 23 days, as reported by 21 TV stations in Denver, Colorado Springs, Grand Junction and Durango.

Democratic groups hold an edge in spending and number of spots purchased, but Republicans are gaining ground.

Much of the advertising is coming from outside spenders, as detailed last week.

But the candidates in three big races are spending, too. Here’s a look.

U.S. Senate

Democratic incumbent Sen. Mark Udall has a tough race against Republican U.S. Rep. Cory Gardner. Most analysts consider the contest a tossup.

Udall went on the air in April and has advertised relatively steadily since then, spending almost $5.2 million.

Gardner started running ads in June, and has spent $4.1 million.

Both candidates have contracts to run ads through Election Day, with Gardner focusing much of his attention on September and early October. Udall is spending more in early September and late October. Most of the contracts illustrated below run for a week at a time.

6th Congressional District

U.S. Rep. Mike Coffman, a three-term GOP congressman, is facing the battle of his political career against former state House Speaker Andrew Romanoff, a Democrat, in another race considered a tossup.

Romanoff began running ads for his campaign in August, spending $1.4 million so far.

Coffman made his first ad buys last week, all for October, spending almost $1.3 million. His October time, focused when ballots are mailed to voters, exceeds Romanoff’s during the same time.

Governor’s race

Incumbent Democratic Gov. John Hickenlooper began buying October ad slots back in May. He now has $1.5 million in ads scheduled, with some slated to begin mid September.

His Republican opponent Bob Beauprez has yet to buy much ad time. Denver station KDVR reported several buys from late September through Nov. 4 last week, totally about $137,000. After winning a four-way primary, Beauprez has plenty of fundraising to do to catch Hickenlooper.

Beauprez, however, has the Republican Governor’s Association (RGA) on his side to the tune of almost $1.2 million in ads. Those ads began in late August and so continue through mid-September.

Starting this week, Beauprez is likely to face some criticism as a $2 million campaign by Making Colorado Great begins to air ads.

Because Beauprez has yet to buy much time, here’s a look at the RGA ads versus Making Colorado Great for September and October so far.

Other advertising

Not all ads run on traditional TV stations or even on TV. Last week, Hickenlooper’s campaign issued this clever online-only retort to the RGA’s first ad.

Sources: This data is compiled by Sandra Fish based on station filings with the Federal Communications Commission and Sunlight Foundation’s Political Ad Sleuth web application.