Just remember mountain climbing can be dangerous anytime of the year. Climbers take a risk with each climb. The desire is to minimize the risks by climbiing at an appropriate time and date, often to avoid potential natural hazards, such as rock and icefall. The one thing that is hardest to plan for is weather. Weather on a large mountain can change rapidly and often without being predicted in forecasts.
I have climbed Mt. Hood via the Cathedral Ridge route and have not tried Cooper Spur, which is the route the climbers are stranded on. The climbers were attempting a rapid ascent with light gear, which means in some terms it was supposed to be up and down in a short timeframe. Commonly refered to as an "Alpine Ascent". The risk is if something goes wrong you have little gear and also if the weather is an issue, as in this case, rescuers are hampered also. The fact that it is December really does not make a climb particularly more risky, but it usually means planning on colder conditions, potential for longer duration storms and variable climbing conditions in regard to snow and ice conditions.
I was once on Mt. Rainier and it snowed 3 feet on us in July at 10,000ft, most years in July there will be no snow to a few inches during a storm at that altitude. Weather on large mountains is just an entity of it's own, especially mountains near to the coast.
The biggest worry for the stranded climbers is if they have enough fuel for their stove to melt water to drink and enough gear to keep frostbite to a minimum if temps are extemely low. That depends on how lightly they packed. Given their experience level, I would say they likely have extra fuel and clothing, sleeping gear and food along. Whether it is enough, that is the worry.
Also, snow caves are really very warm in relation to exposed temperatures outside the cave, that should help keep them safer. No wind will effect them in a snow cave as well.
I give them an excellent chance at survival, if the weather will just let up soon. Time is the enemy in this situation. Pray for the best!