Date: 201407
Local time of day: 1201-1800
Location: JAC.Airport, WY
Flight conditions: Marginal
Weather elements / visibility: Icing; Turbulence
Light: Daylight
Aircraft: Large Transport; Low Wing; 2 Turbojet Eng
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Landing
ATC / advisory: Tower JAC
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Workload; Distraction; Situational Awareness
Second reporter function: Pilot Not Flying; First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Ground Excursion Runway; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Contributing factors: Airport; Weather; Human Factors
Primary problem: Ambiguous

Narrative: Our first attempt was the ILS 19Z JAC. We had observed radar returns from 35-40 miles east that indicated the possibility thunderstorms moving over the airport at our ETA. Due to terrain it was not possible to make an accurate evaluation and we briefed the approach. ATC initially cleared us to FAPMO on the ILS 19Y; which we declined because it is too close in and too close to terrain for a stable approach; they re-cleared us for the ILS 19Z which we had briefed and planned to finish visually.First approach: Before ZOSUV; we called the field and terrain in-sight and were cleared for the visual. As we turned final; the Tower notified us of heavy rain directly over the airport with visibility dropping to 3 miles; our radar return confirmed the condition we had been observing for 20 -25 miles and visual contact showed heavy rain with very dark areas of rain at the airport. Based on possibility of microburst activity and windshear; we abandoned the approach at approximately 7 to 8 miles and requested climb out instructions; we were switched to ZLC for a climb to 15;000 FT on present heading then vectored back to DNW.Second approach: ILS 19Z JAC via DNW. Again I believe at the time Tower winds were reported at 080 at about 15-20 although we were monitoring a slight tailwind on the FMS. On short final the tailwinds had diminished and over the fence winds had shifted to the light from the left so I continued the approach.Landing: We were at idle thrust; well into the flare with airspeed rapidly deteriorating when it became apparent the touchdown may be long; there were indications we had entered an area of a tailwind condition. Although I briefed for a shallow flare and firm landing; the flare seemed long indicative of a possible tailwind. We touched down I would estimate at one third of the runway and immediately went to full reverse thrust with auto brakes medium. In the last 1;000 FT or so of runway; I became concerned with our stopping ability and went to maximum manual braking. Go-around/bounce and go or continue the landing. As we were never trained or practiced in go-arounds from a condition deep into a landing flare with engines idle and airspeed below 100 KTS or touch and go's/bounce and go's from such a condition; it was an unknown realm for me. I elected to continue the landing. We entered the overrun area by approximately 100-150 feet; the Tower asked us if we could turn around from there and we could with no special effort; taxied to the gate and deplaned as usual. I suggest additional training on Special Use Airports.


Second narrative: Improved briefing regarding e.g. specifically verbalizing what to do in the event of a float. Better decision making on the part of the crew to call for a go-around.Possible incorporation of specific short field high density altitude training during initial and recurrent training.


Synopsis: An Air Carrier crew completed their second JAC Runway 19 approach in a crosswind which became a tailwind and were unable to stop on the runway. After over running the runway end by about 100 FT; they returned to the runway and proceeded to the gate.