I have been in Las Vegas during January and February on several occasions. The weather can vary. Most likely it will be sunny and pleasant during the daytime but cool at night. Typically, you can walk around with short-sleeved summer shirts during the afternoon (I have even seen a few brave souls wearing shorts); but after sunset it usually becomes rather cool or even a bit chilly. Occasionally, it rains during the winter months. They only get about two inches of rain per year, but half of that can come in a one or two days rainfall during January or February. If you are unlucky enough to arrive during a rainy spell, do not fear, as the next day or the day after, it will be pleasant and sunny again.
Las Vegas has so many attractions and entertainments that it is difficult to recommend a few. Go to some of the grand casinos on the southern end of the strip, and just look at the extravagant decor and magnificent scale. The giant pyramid of Luxor, the fairytale castle of Excalibar, the scaled-down skyline of New York, the grandness of Caesars Palace, the Eifel Tower in the desert just to name a few. See the free shows at the foutains of Bellagio, the Pirates Cove in front of Treasure Island, and the Mardi Gras at the ceiling of the Rio Casino. Go to old downtown Las Vegas at night and see the magnificent light show above Freemont Street. Eat in several of the many fine restaurants, or the grand all-you-can-eat buffets.
The South Rim of the Grand Canyon is just five hours drive from Las Vegas. Along the way, you can visit some of the old towns that were on the original Route 66 such as Kingman, Seligman and Williams. Just an hour and a half south of the Grand Canyon, Sedona Arizona is one of the most beautiful towns in the Southwest.
In the opposite direction, Los Angeles is just five hours drive from Las Vegas. You don't have to drive all the way to Monterey to see whales. Santa Barbara is only two hours north of Los Angeles. It has as much scenic beauty as Monterey with less commercialization and less congestion. Santa Barbara is the place where many local Californians go on vacation. From Santa Barbara, many tour boats go out whale watching or on excursions to the Channel Islands directly in the migration routes of the whales.