Two Heads are Better than One
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Or in this case, having two possible routes is better than just having a single route that you have to take, no matter what. The fact is that your two major possibilities: 1) I-5 down to Bakersfield, CA-58 t Barstow, and I-15 from there; and 2) I-84 to Twin Falls and US-93 south from there differ by only about 100 miles and an hour of driving. A third possibility, I-84 to north of Salt Lake City and I-15 to Las Vegas also falls within the same general parameters, about 1100 miles and two full days of driving. So what would be the deciding factor in choosing one over the other(s)? Weather, of course. Rather than count on chains, find the route that won't see snow (probably). Right now, the National Weather Service is predicting light rain with little accumulation along all three routes on the 28th, with that precipitation turning to snow on the mountain tops (but not in the valleys or passes). So you can pick any one of the three routes and probably encounter the same weather. You might as well pick the most scenic route or the one you haven't driven yet, because unless you have more than two days for the drive, you won't really be able to stop anywhere except for a good night's sleep.
AZBuck