Date: 201510
Local time of day: 1201-1800
Location: LAS.Airport, NV
Flight conditions: IMC
Light: Daylight
Aircraft: A321
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E L30
ATC / advisory: TRACON L30
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Aircraft Aircraft Damaged
Contributing factors: Weather
Primary problem: Weather

Narrative: On the Tyson arrival into LAS. On this specific arrival the tops ranged from FL200 to FL180; with significantly larger cells to the north and south. However; they were at least 40-50 miles away from our position. We were already deviating off the route for small cells as depicted on the radar. We entered an area to the SE of Tyson Intersection; that looking at the radar would keep us clear of the small cells as depicted. We entered the clouds approximately FL190. Descending through approx. FL150 we entered an area of moderate/severe hail for about 10 seconds. The Aircraft was clean; slowed to 250 knots with igniters on. The event was over as quick as it started and we were again in VMC conditions; with scattered clouds. ATC was advised. An uneventful landing followed on 25L. Company ops was advised to notify maintenance to standby to inspect Aircraft for possible damage. A logbook write-up was made as well as a verbal report to the controlling dispatcher.Considering our avoidance efforts; the shape and tops of the clouds and what was being painted on the radar; I still remain stunned that hail to that severity was in the vicinity of the weather we were maneuvering around. When I suggest all reasonable efforts were taken to avoid the severe weather; I mean it sincerely. From the time of the event and now; I have racked my brain on how we could have avoided damage to the Aircraft and have come to no viable conclusions.


Second narrative: We were flying an enhanced 321 to Las Vegas midday; executing the Tyssn 3 arrival for a visual approach 25L. There was a 'train' of cells moving from the SE from Mexico which had been affecting weather in Las Vegas all day; causing heavy rain and hail in the valley. As I recall the ATIS published the hour before we arrived reported a cell over the field and heavy rain; with reports of hail up to 1' in parts of the valley; but not on the field. We started painting weather a couple of hundred miles from the field so were paying pretty close attention to the path we would need to take to get into Vegas.By the time we began to fly the arrival the cells had moved well to the north of the airport; rain had stopped and the airport was VMC. We were painting a line of weather running SSW to NNE 35 miles east of the field with a cell approximately 40 miles south of our course and another 30 to 40 miles to the north; but no weather of consequence between us and the airport. Visually we could see a storm on the west side of the valley immediately opposite the airport with rain falling on the mountains on the western side of the valley; 15 miles to the west of the airport; but with the winds coming from the SSW this wasn't an issue since any hail would blow to the north.While flying the arrival we painted a small cell between KADDY and TYSSN intersections and deviated just a little to the south to avoid it. It was only showing a little moderate (yellow) rain and we estimated the tops to be about 18000 but we avoided it anyway since it looked likely to be bumpy. There was also a smaller Cumulus (CU) just to the south of our course but we estimated those tops to be even lower; maybe 15 to 16000 feet. Between the two CUs there was a layer of stratus. I would estimate the gap between the two CUs to be about 5 miles. We planned to pass between them; which was painting clear but consisted of stratus; and turn right to pass abeam KADDY at 12000 feet and 250 knots. As we entered the stratus we were at idle power; nearing 250 knots descending through approximately 14000 feet.Within a few seconds of entering the stratus we encountered hail. It was very; very noisy; the loudest thing I've experienced in 38 years of flying. Visibility was zero but we could see the hail hitting the windscreen and blowing up. We cleared the hail in what I would guess to be under 30 seconds and exited the stratus layer a few seconds later. I immediately advised ATC about the encounter so they could protect other aircraft. The Captain and I then turned our attention to assessing the engines and fly-ability of the aircraft; all of which were fine. We caught our breath and completed the arrival and landed on runway 25L.On post flight the engines and leading edge devices appeared to be fine but the leading edge of the horizontal stabilizer was badly damaged and the radome had some missing and blistered paint. The fan blades appeared to be unscathed.I've penetrated squall lines many times in my career. This occasion seemed to be one of the simpler ones since the large cells were so far away. I've bypassed moderate cumulus clouds like this thousands of times. So has the captain. I can only categorize finding hail in this cloud as extraordinarily unusual. The theory of hail development I learned years ago required high cumulus clouds; well above the freezing level. Tiny ice pellets would form; drop; be lifted again; refreeze; drop; get wet; lift; refreeze; over and over again to grow in size and then drop to the ground. Later theory proposed that they could be ejected out the top and then carried by winds aloft downwind of the cell to then fall to the earth in clear air. This is something we all try to avoid; thus giving a wide berth to large and mature cells. Later theory postulated that ice pellets could remain at a constant altitude; sitting in freezing conditions and rising air; growing in size without either rising or falling. Neither of these wouldseem to account for our encounter. The CUs we flew between were just too small; the larger having tops to about 18000 and having a diameter of approximately 8 miles. Neither was painting anything more than moderate rain. We had enhanced radar and we knew it was working because we were painting much nastier cells (and I'm pretty sure it was in full Auto mode which works very well). The cell we were downwind of was approximately 40 miles away. That seems an unlikely but still possible culprit.The National Weather Service states that dry hail has a very low radar return and wet hail has amongst the highest. I can only assume then with NO radar return the hail we went through was dry and not in the formative state; which would mean it originated somewhere else. It would seem unlikely that wind would carry it for 40 miles which was the closest cell capable of developing this size hail under any theory that I'm familiar with; so I'm at a loss to say where it came from.


Synopsis: A321 flight crew encountered large hail at 14;000 feet during descent into LAS. The crew was passing through stratus clouds with no radar returns and no large thunderstorms were in the area. After landing the horizontal stabilizer was found to be badly damaged.