Aconcagua page-at the bottom of the permit section there is this information:
Off –season (from March 16 to November 14) access to the Aconcagua Park is no longer free. A permit must be purchased in Mendoza or at the Park Rangers’ Shelter in Horcones Valley. The price of admittance is the price charged during the high season even if the rescuing service is not provided. Neither doctors nor park rangers are available during this period. However, for a “special” price, there is an exception between March 16 and April 1st., of each season.
To access the Aconcagua Park within these periods, for trekkings or to climb, we suggest contacting the Aconcagua Park’s authorities. There are restrictions regarding the access of MINORS to the Park: they will have to exhibit pertinent authorization signed by both parents and certified by Public Notary or their respective Consulate or Embassy. For further information, please, contact the RENOVABLE NATURAL RESOURCES BUREAU (Dirección de Recursos Naturales Renovables) located in General San Martín Park, phone + 54 261 425 5090 or + 54 261 425 7065 (from 08:00 AM to 01:00 PM) e mail: email@example.com
At the very bottom of the page there is this information from Boris Krielen.
I have climbed Aconcagua and reached the summit friday 29th of March 2002 during the Viento Blanco, the terrible snowstorm. As I was going to high camp, I was the only one in the park, quite an exclusive experience! After the summit, going down through the fresh snow was pretty cool, though routefinding becomes more difficult and danger of avalanche grows. Routefinding during the Viento Blanco is extremely hard. GPS can be a help. Local brochure has a list of waypoints. I didn't take a GPS. In advance, government people told me by e-mail to pay US$ 200 for the permit and US$ 70 more for several legal services and notary-papers. This turned out to be all nonsense. I paid 40 pesos at the entry of the park. Entering the park in high winter - June/September - might be more difficult though. Government and park officials indeed don't encourage this. Danger of avalanche is huge then.
After 16th of March there are no mules available from Puente del Inca or Punta de Vacas. Mules are not allowed into the park between 16th of March and 15th of November. Outfitters bring the mules down to Mendoza for the wintertime. Therefore I was the mule myself, carrying 32 kilo's. That's the way a real solo-expedition should be like, I think.
There are no wide rivers to pass on the normal route. On route to Plaza Argentina (Polish Glaciar) the river has to be passed at least twice. This could be a problem without mules. Until July, don't count on snowbridges to cross the rivers lower in the valley. Take a towel and light shoes!
That is all I know. Perhaps you should contact Boris (I searched for his user name but came up empty). Some things have changed for sure like the permits being the same price as the high season but the conditions will be relatively the same as when he went. You will just get no rescue support as there will be no rangers in the park.
1. What is the best time in Winter?
2. What is the weather like?
(Cold, snow and storms)
3. How much snow falls?
(Varies from year to year)
4. Sure there will be winter storms, but how frequent and long will the clear spells be?
( In the summer the weather systems seem to last 5 days, on average. This mountain creates its own weather however. Have not been there in the winter to say if this pattern remains constant)
5. How cold does it get?
(Burrrr. it can be -30c in the summer so the winter... I don't know)
6. Are the rivers frozen over?
7. Will the bridges be usable?
8. How bad is the avalanche danger?
(Will depend on the conditions. Plaza des mulas and Camp Canada would be in the line of fire in my mind)
9. Will the Berlin hut be usable?
(The new one should be OK. Will be partly covered with snow probably. The old ones are ruined. Thanks for the update Ario)
10. Is there enough snow for to use skis and a sled the whole way?
(I would imagine so. But each winter would be different. Last year there was record snow)
11. Will there be technical climbing on the Normal Route?
12. Will we need rope and pro? If not on the route, how about crossing the rivers? (Should be no problem on the normal route, Big issue in the Vacas approach and would avoid this route myself)
13. Do we need a permit?
14. Is transportation available from Mendoza?
(as far as the ski resort, Penetentes. The bus usually stops at Puenta del Inca but I am unsure if the hostel is open in the winter. The ski resort is at Penetentes)
15. What is the average time for a winter trip?
(I would guess 16 days)
16. Will there be any other climbers?
(Most likely no)
17. Is the Polish Glacier feasible in Winter?
(I would think it would be avalanche prone, and you would have to approach from the normal route by doing the traverse in reverse)
18. Do radios work?
(Yes, depending on where you are)
19. How good is that ski resort near the trail head?
20. Am I cracked?