I looked up your info as I had no idea what was LittleYellow Jacket and saw it was a bull that was recently inducted into the cowboy hall of fame.
Well...I dont know if January is the best time of year to vist from SoCal....but weather can vary greatly from day to day and one winter to the next. This year overall we are expecting a drier and warmer January than "normal"...but that doesnt mean it will not get very cold though. Normals for Bismarck for mid January....are high temp of 20 and low of -1. Temperatures though can vary tremendously...if we have an arctic outbreak it can be zero during the day and -25 or -30 at night and then again could see highs as warm as 35 and lows of 20. No snow on the ground Bismarck at the present time....and snowfall again can be quite variable. In most years there is snowcover but Bismarck is in the warm part of the state so snowcover does not tend to stick around as long as where I live in northeastern ND/northwestern MN.
Best bet is to check the weather a few days before flying up and then bring along clothes accordingly. I would strongly advise to use the National Weather Service web page for the Bismarck office as the forecast as national cable channels, etc do not talk much about our area. The web link is
http://www.nws.noaa.gov/bis
Road conditions again could be variable...but if no snow then roads are plowed and sanded good so travel should be o.k. Just rent at least a front wheel drive vehicle.
By the way I work for the NWS office in Grand Forks....which is quite a bit colder and snowier than Bismarck. Hope you enjoy your visit whenever you come.
Dan