The remnants of Hurricane Rosa in the Pacific Ocean will combine with a trough of low pressure moving into California to deliver rain chances to Las Vegas early next week.
Rain is likely on Monday and Tuesday, and possible Wednesday and perhaps even Thursday. The increased clouds and rain chances will drop highs to the 80s for a few days in a row for the first time since May. It has not rained at McCarran Airport since Aug. 11 and by the time wet weather is possible on Monday it will have been 51 days in a row with dry conditions.
Some computer models suggest more than 1" of rain with this system (mainly Monday and Tuesday). In the 81 years in Las Vegas' weather history, it has only rained 1" or more on 28 calendar days (the last time was January 9, 2018). Furthermore, only two of those wet days were in October. It is rare to predict heavy rain this time of fall, but it is possible with the interaction of a tropical system.
Given the length of time since our last widespread rain, it would make sense to expect slippery roadways if rain falls on Monday and Tuesday as the dirt and oil becomes loose.