Normal snowfall will make the trip not passable or extremely dangerous.
A great workout if you do the full 10 miles (round trip) from the highway. You should expect to see great views of the Sierras along the way, and particularly when you get to the lookout point.
Need To Know
Needle Springs starts the trailhead which is 3 miles from the highway. It is mostly shaded along the trail and plenty to be found. There is no water along the trail.
Depending on the time of year that you visit a gate may block your entrance to the upper parking area. If the gate is closed, you'll need to park lower, adding mileage to your outing. Additionally, the trail may have parts where snow remains through the spring and it can be difficult to pass. You may also run into several spots with down trees. Expect a longer outing under those conditions as you'll often have to navigate your own trails.
This route covers 10 miles round trip, but can be shortened by 3 miles each way if the gate to the trailhead is open. The gate is just a few feet off the road, and there is a large metal sign on the road, but it is getting weathered. Along the way you'll have plenty of great views of the eastern Sierras.
At the trailhead, there is a restroom and a campground, but again, be sure it is open before you count on it.
It is mostly uphill to the trailhead but the grade is steep only in a few places. Once you hit the trailhead, you have a couple of mountains to navigate up and down with the final climb up the switchbacks to the lookout. The trail is typically 4-5 feet wide, but narrows to just a couple feet in many places. Snow, which lasted until at least May in some years, can make the trail difficult to pass in several areas where the trail is a single path and the drop is quite steep. In the summer months, snow will not be an issue. You may have to jump over a few downed trees measuring 2-3 feet in diameter.
Just before your ascent up the last peak, there is a small campground where you can take a breather, as well as an area up the peak, but before the steps where you can circle up. The final climb is all singletrack up the switchbacks to the lookout steps and is rocky.
The lookout is no longer there, but the steps up to where it used to be are still there and safe. Once at the top, you can see Dome Rock (which you can get to via a less intense trail which you can access along the same highway) to the south.
History & Background
Check out this page for info on the fire which destroyed the lookout: buckrock.org/needles.html