A summer of big news stories and big weather propelled Fox News Channel to record viewership in the third quarter, the fifth consecutive quarter in which Fox News’ ratings outperformed those of its competitors combined.

Fox News outdrew the competition despite the fact that CNN recorded the largest year-to-year gains in stormy September.

Fox stacked up its biggest quarterly audience ever in prime time, an average of 2.3 million viewers, which was up 29 percent from third quarter 2004, according to data from Nielsen Media Research. The news network also was the top cable network in prime time in September and the No. 2 cable network, behind TNT (2.7 million viewers), for the three months.

Leading Fox’s record-setting prime-time charge was “On the Record With Greta Van Susteren,” which averaged 2.41 million viewers for the third quarter, a 53 percent increase over the show’s third quarter 2004 average. The show ended the quarter within whispering distance of Fox stablemate “Hannity & Colmes,” which averaged 2.44 million viewers (up 25 percent year-to-year). “The O’Reilly Factor” remained the most-watched cable news show with 2.8 million viewers Filling out the top five were Fox News’ “The Fox Report With Shepard Smith” (1.8 million viewers) and the network’s “Special Report With Brit Hume” (1.5 million).

CNN’s “Larry King Live” (1.5 million) ranked sixth for the third quarter and broke Fox’s grip on the top 12 cable news programs. Cable news networks across the board experienced year-to-year viewership boosts in September, except for CNBC’s prime-time lineup, which dropped 5 percent to an average of 126,000 viewers.

After CNN’s Wolf Blitzer-anchored “Situation Room” debuted Aug. 8, it averaged 1.1 million viewers, a 102 percent increase year to year in the 3-6 p.m. weekday block, where it faces FNC’s “Studio B With Shepard Smith” (1.7 million viewers for the quarter, up 66 percent from the comparable period in 2004), “Your World With Neil Cavuto” (1.5 million, up 47 percent), and “The Big Story With John Gibson” (1.6 million, up 38 percent).

MSNBC tied CNN Headline News (471,000 viewers apiece) in prime time for the quarter. In total day, MSNBC slipped past Headline News for the first time since April to finish third with 300,000 viewers, while Headline News finished fourth (267,000).

The bright spot for MSNBC was “Rita Cosby: Live and Direct,” which, like CNN’s “Situation Room,” launched Aug. 8. “Cosby” boosted the 9 o’clock weeknight time slot launch to date by 15 percent year to year. Compared with the second quarter of 2005, the show is up 71 percent to an average of 488,000 viewers.

The four news networks finished the quarter with double-digit year-to-year improvements among 25- to 54-year-old viewers. Fox led with an average 404,000 viewers in the demo for total day. CNN averaged 260,000. MSNBC averaged 132,000. Headline News posted 114,000.