On June 4, 2004, at 1817 central daylight time (CDT), a Boeing 737-7H4, N757LV, operated by Southwest Airlines Co. (SWA) as flight 2297, encountered turbulence approximately 15 nautical miles (NM) southeast of Liberal, Kansas (LBL), during cruise flight at flight level (FL) 370. One flight attendant was seriously injured. The flight then diverted to Kansas City International Airport, Kansas City, Missouri, where it landed without further incident. Visual and instrument meteorological conditions with convective activity prevailed at the time of the accident. The scheduled domestic passenger flight was operating on an instrument rules flight plan under the provisions of Title 14 Code of Federal Regulations Part 121. The 2 flight crew members, 2 remaining flight attendants, and 131 passengers reported no injuries. The flight departed from Phoenix Sky Harbor International Airport, Phoenix, Arizona, at 1650 mountain daylight time, and was en route to Port Columbus International Airport, Columbus, Ohio. According to SWA's Director of Flight Operational Safety, flight 2297 had been in cruise flight at FL370. The flight was in cirrus and in and out of cloud tops experiencing some light chop for the last 100-150 miles. The seat belt sign was on with all passengers seated. The radar was in turbulence mode. The crew had been watching cells with heavy rain and turbulence just north of the Amarillo, Texas, area and the airplane passed well north on the upwind side. Near LBL, they saw a patch of blue sky to the right front and painted nothing in front of them. The encounter occurred when a large buildup appeared in front of the airplane with less than two seconds notice. The airplane experienced airspeed excursions from about 275 knots to 225 knots with an altitude loss of 500 feet. During the encounter, the airplane also experienced small hail. Other aircraft in the area reported no conditions greater than light [turbulence]. Just prior to the encounter, the captain released the flight attendants to resume service. The 'A' flight attendant informed the flight crew that as the flight attendants in the galley removed their seat belts, the 'B' flight attendant became injured. No emergency was declared. The following are transcribed transmissions between SWA flight 2297, Kansas Air Route Traffic Control Center R23 and R09 positions, and an unknown Kansas Air Route Traffic Control Center controller (UNK). The following transcription times are based upon CDT. 1816:54, SWA flight 2297, "southwest uh twenty two ninety seven we'd like to take a right turn here south for uh some weather" 1817:02, R23, "southwest twenty two ninety seven approved as requested direct saint louis uh when able" 1817:07, SWA flight 2297, "southwest twenty two ninety seven" 1817:19, SWA flight 2297, "uh southwest twenty two ninety seven there's a buildup right there that's not showing radar that we got some uh moderate to severe turbulence here we're climbing back to three seven zero" 1817:29, R23, "roger uh just uh one small pocket there" 1817:31, SWA flight 2297, yeah didn't show up on radar at all" 1817:34, R23, "i'm not showing anything either" 1819:02, R23, "southwest twenty two ninety seven was that right on the uh edge of the weather" 1819:07, SWA flight 2297, "uh southwest uh twenty two ninety seven say again please" 1819:09, R23, "was that right on the edge of the weather uh or after you were in the clear" 1819:13, SWA flight 2297, "actually we were just uh we been just skimming through the tops it's kind of a haze layer and like i said we were uh painting that cell that was just north of amarillo but that one did not show at all so uh it was a build up that was inside of the haze we didn't even see it" 1819:28, R23, "all right thanks for that southwest twenty two ninety seven contact kansas city center now one three three point two" 1819:32, SWA flight 2297, "thirty three two thanks" 1819:56, SWA flight 2297, "and before we go here twenty two ninety seven there was some hail in that stuff as well" 1820:02, R3, "some hail in there (unintelligible)" 1820:03, SWA flight 2297, "affirmative and uh pretty good down drafts we lost five hundred feet" 1820:06, R23, "all right thanks" 1820:24, R23, "go ahead" 1820:26, UKN, "hey what's the deal with southwest twenty two ninety seven could you ask him how his ride was through that thunderstorm we got company wanting to know" 1820:34, R23, "he uh just south of liberal he encountered a cell that he said he wasn't painting that he got uh moderate to severe turbulence lost five hundred feet hail in there and uh just one little blip there and then it was done but otherwise (unintelligible)" 1830:52, UNK, "okay that was southwest" 1820:54, R23, "yeah" 1820:09, SWA flight 2297, "center southwest twenty two ninety seven is flight level three seven zero" 1820:12, R06, "southwest twenty two ninety seven kansas city center roger" 1828:27, SWA flight 2297, "that was us that was uh twenty two ninety seven" 1828:27, R06, "southwest twenty two ninety seven roger were you at flight level three seven zero at that time" 1828:34, SWA flight 2297, "that's affirmative it was only lasted for uh --- oh --- i'd say a minute minute and a half it was an area of weather that uh had tops above three seven zero that did not show on (unintelligible)" 1828:47, R06, "and you said that was out around liberal or where exactly was that" 1828:50, SWA flight 2297, "it was almost right on top of liberal three seven zero" 1828:54, R06, "okay" 1828:58, SWA flight 2297, "we were flying in the haze an uh (unintelligible) right in the middle there's also some hail in there" SWA download the airplane's flight data recorder and reported the maximum vertical accelerations during the turbulence encounter were +1.7 g and -0.258 g. The airplane landed without further incident and the company reported the airplane did not sustain any damage. The flight attendant sustained a broken ankle. Convective SIGMET 75C, valid until 1955 CDT, was issued for an area from 40 NM west northwest of LBL to 40 NM north-northwest of Amarillo, Texas, to 30 NM south-southwest of Tucumcari, New Mexico, to 30 NM east of Tobe, Colorado, to 40 NM west-northwest of LBL. The SIGMET stated: area of severe thunderstorms moving little; tops to FL 400; hail to 2.5 inches; wind gusts to 60 knots possible. The Federal Aviation Administration and SWA were parties to the investigation.